1.The
Java interpreter is used for the
execution of the source code.
True
False
Ans:
a.
2)
On successful compilation a file with the class extension is created.
a)
True
b)
False
Ans:
a.
3)
The Java source code can be created in a Notepad editor.
a)
True
b)
False
Ans:
a.
4)
The Java Program is enclosed in a class definition.
a)
True
b)
False
Ans:
a.
5)
What declarations are required for every Java application?
Ans:
A class and the main( ) method declarations.
6)
What are the two parts in executing a Java program and their purposes?
Ans:
Two parts in executing a Java program are:
Java
Compiler and Java Interpreter.
The
Java Compiler is used for compilation and the Java Interpreter is used for
execution of the application.
7)
What are the three OOPs principles and define them?
Ans
: Encapsulation, Inheritance and Polymorphism are the three OOPs
Principles.
Encapsulation:
Is
the Mechanism that binds together code and the data it manipulates, and keeps
both safe from outside interference and misuse.
Inheritance:
Is
the process by which one object acquires the properties of another object.
Polymorphism:
Is
a feature that allows one interface to be used for a general class of actions.
8)
What is a compilation unit?
Ans
: Java source code file.
9)
What output is displayed as the result of executing the following statement?
System.out.println("//
Looks like a comment.");
//
Looks like a comment
The
statement results in a compilation error
Looks
like a comment
No
output is displayed
Ans
: a.
10)
In order for a source code file, containing the public class Test, to
successfully compile, which of the following must be true?
It
must have a package statement
It
must be named Test.java
It
must import java.lang
It
must declare a public class named Test
Ans
: b
11)
What are identifiers and what is naming convention?
Ans
: Identifiers are used for class names, method names and variable names. An
identifier may be any descriptive sequence of upper case & lower case
letters,numbers or underscore or dollar sign and must not begin with numbers.
12)
What is the return type of program’s main( ) method?
Ans
: void
13)
What is the argument type of program’s main( ) method?
Ans
: string array.
14)
Which characters are as first characters of an identifier?
Ans
: A – Z, a – z, _ ,$
15)
What are different comments?
Ans
: 1) // -- single line comment
2)
/* --
*/
multiple line comment
3)
/** --
*/
documentation
16)
What is the difference between constructor method and method?
Ans
: Constructor will be automatically invoked when an object is created. Whereas
method has to be call explicitly.
17)
What is the use of bin and lib in JDK?
Ans
: Bin contains all tools such as javac, applet viewer, awt tool etc., whereas
Lib
contains
all packages and variables.
Data types,variables and Arrays
1)
What is meant by variable?
Ans:
Variables are locations in memory that can hold values. Before assigning any
value to a variable, it must be declared.
2)
What are the kinds of variables in Java? What are their uses?
Ans:
Java has three kinds of variables namely, the instance variable, the local
variable and the class variable.
Local
variables are used inside blocks as counters or in methods as temporary
variables and are used to store information needed by a single method.
Instance
variables are used to define attributes or the state of a particular object and
are used to store information needed by multiple methods in the objects.
Class
variables are global to a class and to all the instances of the class and are
useful for communicating between different objects of all the same class or
keeping track of global states.
3)
How are the variables declared?
Ans:
Variables can be declared anywhere in the method definition and can be
initialized during their declaration.They are commonly declared before usage at
the beginning of the definition.
Variables
with the same data type can be declared together. Local variables must be given
a value before usage.
4)
What are variable types?
Ans:
Variable types can be any data type that java supports, which includes the
eight primitive data types, the name of a class or interface and an array.
5)
How do you assign values to variables?
Ans:
Values are assigned to variables using the assignment operator =.
6)
What is a literal? How many types of literals are there?
Ans:
A literal represents a value of a certain type where the type describes how
that value behaves.
There
are different types of literals namely number literals, character literals,
boolean
literals, string literals,etc.
7)
What is an array?
Ans:
An array is an object that stores a list of items.
8)
How do you declare an array?
Ans:
Array variable indicates the type of object that the array holds.
Ex:
int arr[];
9)
Java supports multidimensional arrays.
a)True
b)False
Ans:
a.
10)
An array of arrays can be created.
a)True
b)False
Ans:
a.
11)
What is a string?
Ans:
A combination of characters is called as string.
12)
Strings are instances of the class String.
a)True
b)False
Ans:
a.
13)
When a string literal is used in the program, Java automatically creates instances
of the string class.
a)True
b)False
Ans:
a.
14)
Which operator is to create and concatenate string?
Ans:
Addition operator(+).
15)
Which of the following declare an array of string objects?
String[
] s;
String
[ ]s:
String[
s]:
String
s[ ]:
Ans
: a, b and d
16)
What is the value of a[3] as the result of the following array declaration?
1
2
3
4
Ans
: d
17)
Which of the following are primitive types?
byte
String
integer
Float
Ans
: a.
18)
What is the range of the char type?
0
to 216
0
to 215
0
to 216-1
0
to 215-1
Ans.
d
19)
What are primitive data types?
Ans
: byte, short, int, long
float,
double
boolean
char
20)
What are default values of different primitive types?
Ans
: int - 0
short
- 0
byte
- 0
long
- 0 l
float
- 0.0 f
double
- 0.0 d
boolean
- false
char
- null
21)
Converting of primitive types to objects can be explicitly.
a)True
b)False
Ans:
b.
22)
How do we change the values of the elements of the array?
Ans
: The array subscript expression can be used to change the values of the elements
of the array.
23)
What is final varaible?
Ans
: If a variable is declared as final variable, then you can not change its
value. It becomes constant.
24)
What is static variable?
Ans
: Static variables are shared by all instances of a class.
Operators
1)
What are operators and what are the various types of operators available in
Java?
Ans:
Operators are special symbols used in expressions.
The
following are the types of operators:
Arithmetic
operators,
Assignment
operators,
Increment
& Decrement operators,
Logical
operators,
Biwise
operators,
Comparison/Relational
operators and
Conditional
operators
2)
The ++ operator is used for incrementing and the -- operator is used for
decrementing.
a)True
b)False
Ans:
a.
3)
Comparison/Logical operators are used for testing and magnitude.
a)True
b)False
Ans:
a.
4)
Character literals are stored as unicode characters.
a)True
b)False
Ans:
a.
5)
What are the Logical operators?
Ans:
OR(|), AND(&), XOR(^) AND NOT(~).
6)
What is the % operator?
Ans
: % operator is the modulo operator or reminder operator. It returns the
reminder of dividing the first operand by second operand.
7)
What is the value of 111 % 13?
3
5
7
9
Ans
: c.
8)
Is &&= a valid operator?
Ans
: No.
9)
Can a double value be cast to a byte?
Ans
: Yes
10)
Can a byte object be cast to a double value ?
Ans
: No. An object cannot be cast to a primitive value.
11)
What are order of precedence and associativity?
Ans
: Order of precedence the order in which operators are evaluated in
expressions.
Associativity
determines whether an expression is evaluated left-right or right-left.
12)
Which Java operator is right associativity?
Ans
: = operator.
13)
What is the difference between prefix and postfix of -- and ++ operators?
Ans
: The prefix form returns the increment or decrement operation and returns the
value of the increment or decrement operation.
The
postfix form returns the current value of all of the expression and then
performs
the increment or decrement operation on that value.
14)
What is the result of expression 5.45 + "3,2"?
The
double value 8.6
The
string ""8.6"
The
long value 8.
The
String "5.453.2"
Ans
: d
15)
What are the values of x and y ?
x =
5; y = ++x;
Ans
: x = 6; y = 6
16)
What are the values of x and z?
x =
5; z = x++;
Ans
: x = 6; z = 5
Control Statements
1)
What are the programming constructs?
Ans:
a) Sequential
b)
Selection -- if and switch statements
c)
Iteration -- for loop, while loop and do-while loop
2)
class conditional {
public
static void main(String args[]) {
int
i = 20;
int
j = 55;
int
z = 0;
z =
i < j ? i : j; // ternary operator
System.out.println("The
value assigned is " + z);
}
}
What
is output of the above program?
Ans:
The value assigned is 20
3)
The switch statement does not require a break.
a)True
b)False
Ans:
b.
4)
The conditional operator is otherwise known as the ternary operator.
a)True
b)False
Ans:
a.
5)
The while loop repeats a set of code while the condition is false.
a)True
b)False
Ans:
b.
6)
The do-while loop repeats a set of code atleast once before the condition is
tested.
a)True
b)False
Ans:
a.
7)
What are difference between break and continue?
Ans:
The break keyword halts the execution of the current loop and forces control
out of the loop.
The
continue is similar to break, except that instead of halting the execution of
the loop, it starts the next iteration.
8)
The for loop repeats a set of statements a certain number of times until a
condition is matched.
a)True
b)False
Ans:
a.
9)
Can a for statement loop indefintely?
Ans
: Yes.
10)
What is the difference between while statement and a do statement/
Ans
: A while statement checks at the beginning of a loop to see whether the next
loop iteration should occur.
A
do statement checks at the end of a loop to see whether the next iteration of a
loop should occur. The do statement will always execute the body of a loop at
least once.
Introduction to Classes and Methods
1)
Which is used to get the value of the instance variables?
Ans:
Dot notation.
2)
The new operator creates a single instance named class and returns a
reference
to that object.
a)True
b)False
Ans:
a.
3)
A class is a template for multiple objects with similar features.
a)True
b)False
Ans:
a.
4)
What is mean by garbage collection?
Ans:
When an object is no longer referred to by any variable, Java automatically
reclaims
memory used by that object. This is known as garbage collection.
5)
What are methods and how are they defined?
Ans:
Methods are functions that operate on instances of classes in which they are
defined.Objects can communicate with each other using methods and can call
methods in other classes.
Method
definition has four parts. They are name of the method, type of object or
primitive type the method returns, a list of parameters and the body of the
method.
A
method's signature is a combination of the first three parts mentioned above.
6)
What is calling method?
Ans:
Calling methods are similar to calling or referring to an instance variable.
These methods are accessed using dot notation.
Ex:
obj.methodname(param1,param2)
7)
Which method is used to determine the class of an object?
Ans:
getClass( ) method can be used to find out what class the belongs to. This
class is defined in the object class and is available to all objects.
8)
All the classes in java.lang package are automatically imported when
a
program is compiled.
a)True
b)False
Ans:
a.
9)
How can class be imported to a program?
Ans:
To import a class, the import keyword should be used as shown.;
import
classname;
10)
How can class be imported from a package to a program?
Ans:
import java . packagename . classname (or) import java.package name.*;
11)
What is a constructor?
Ans:
A constructor is a special kind of method that determines how an object is
initialized
when created.
12)
Which keyword is used to create an instance of a class?
Ans:
new.
13)
Which method is used to garbage collect an object?
Ans:
finalize ().
14)
Constructors can be overloaded like regular methods.
a)True
b)False
Ans:
a.
15)
What is casting?
Ans:
Casting is bused to convert the value of one type to another.
16)
Casting between primitive types allows conversion of one primitive type to
another.
a)True
b)False
Ans:
a.
17)
Casting occurs commonly between numeric types.
a)True
b)False
Ans:
a.
18)
Boolean values can be cast into any other primitive type.
a)True
b)False
Ans:
b.
19)
Casting does not affect the original object or value.
a)True
b)False
Ans:
a.
20)
Which cast must be used to convert a larger value into a smaller one?
Ans:
Explicit cast.
21)
Which cast must be used to cast an object to another class?
Ans:
Specific cast.
22)
Which of the following features are common to both Java & C++?
A.The
class declaration
b.The
access modifiers
c.The
encapsulation of data & methods with in objects
d.The
use of pointers
Ans:
a,b,c.
23)
Which of the following statements accurately describe the use of access
modifiers within a class definition?
a.They
can be applied to both data & methods
b.They
must precede a class's data variables or methods
c.They
can follow a class's data variables or methods
d.They
can appear in any order
e.They
must be applied to data variables first and then to methods
Ans:
a,b,d.
24)
Suppose a given instance variable has been declared private.
Can
this instance variable be manipulated by methods out side its class?
a.yes
b.no
Ans:
b.
25)
Which of the following statements can be used to describe a public method?
a.It
is accessible to all other classes in the hierarchy
b.It
is accessablde only to subclasses of its parent class
c.It
represents the public interface of its class
d.The
only way to gain access to this method is by calling one of the public class
methods
Ans:
a,c.
26)
Which of the following types of class members can be part of the internal part
of a class?
a.Public
instance variables
b.Private
instance variables
c.Public
methods
d.Private
methods
Ans:
b,d.
27)
You would use the ____ operator to create a single instance of a named class.
a.new
b.dot
Ans:
a.
28)
Which of the following statements correctly describes the relation between an
object and the instance variable it stores?
a.Each
new object has its own distinctive set of instance variables
b.Each
object has a copy of the instance variables of its class
c.the
instance variable of each object are seperate from the variables of other
objects
d.The
instance variables of each object are stored together with the variables of
other objects
Ans:
a,b,c.
29)
If no input parameters are specified in a method declaration then the
declaration will include __.
a.an
empty set of parantheses
b.the
term void
Ans:
a.
30)
What are the functions of the dot(.) operator?
a.It
enables you to access instance variables of any objects within a class
b.It
enables you to store values in instance variables of an object
c.It
is used to call object methods
d.It
is to create a new object
Ans:
a,b,c.
31)
Which of the following can be referenced by this variable?
a.The
instance variables of a class only
b.The
methods of a class only
c.The
instance variables and methods of a class
Ans:
c.
32)
The this reference is used in conjunction with ___methods.
a.static
b.non-static
Ans:
b.
33)
Which of the following operators are used in conjunction with the this and
super references?
a.The
new operator
b.The
instanceof operator
c.The
dot operator
Ans:
c.
34)
A constructor is automatically called when an object is instantiated
a.
true
b.
false
Ans:
a.
35)
When may a constructor be called without specifying arguments?
a.
When the default constructor is not called
b.
When the name of the constructor differs from that of the class
c.
When there are no constructors for the class
Ans:
c.
36)
Each class in java can have a finalizer method
a.
true
b.false
Ans:
a.
37)
When an object is referenced, does this mean that it has been identified by the
finalizer method for garbage collection?
a.yes
b.no
Ans:
b.
38)
Because finalize () belongs to the java.lang.Object class, it is present in all
___.
a.objects
b.classes
c.methods
Ans:
b.
39)
Identify the true statements about finalization.
a.A
class may have only one finalize method
b.Finalizers
are mostly used with simple classes
c.Finalizer
overloading is not allowed
Ans:
a,c.
40)
When you write finalize() method for your class, you are overriding a finalizer
inherited
from a super class.
a.true
b.false
Ans:
a.
41)
Java memory management mechanism garbage collects objects which are no longer
referenced
a
true
b.false
Ans:
a.
42)
are objects referenced by a variable candidates for garbage collection when the
variable goes out of scope?
a
yes
b.
no
Ans:
a.
43)
Java's garbage collector runs as a ___ priority thread waiting for __priority
threads to relinquish the processor.
a.high
b.low
Ans:
a,b.
44)
The garbage collector will run immediately when the system is out of memory
a.true
b.false
Ans:
a.
45)
You can explicitly drop a object reference by setting the value of a variable
whose data type is a reference type to ___
Ans:
null
46)
When might your program wish to run the garbage collecter?
a.
before it enters a compute-intense section of code
b.
before it enters a memory-intense section of code
c.
before objects are finalized
d.
when it knows there will be some idle time
Ans:
a,b,d
47)
For externalizable objects the class is solely responsible for the external
format of its contents
a.true
b.false
Ans:
a
48)
When an object is stored, are all of the objects that are reachable from that
object stored as well?
a.true
b.false
Ans:
a
49)
The default__ of objects protects private and trancient data, and supports the
__ of the classes
a.evolution
b.encoding
Ans:
b,a.
50)
Which are keywords in Java?
a)
NULL
b)
sizeof
c)
friend
d)
extends
e)
synchronized
Ans
: d and e
51)
When must the main class and the file name coincide?
Ans
:When class is declared public.
52)
What are different modifiers?
Ans
: public, private, protected, default, static, trancient, volatile, final, abstract.
53)
What are access modifiers?
Ans
: public, private, protected, default.
54)
What is meant by "Passing by value" and " Passing by
reference"?
Ans
: objects – pass by referrence
Methods
- pass by value
55)
Is a class a subclass of itself?
Ans
: A class is a subclass itself.
56)
What modifiers may be used with top-level class?
Ans
: public, abstract, final.
57)
What is an example of polymorphism?
Inner
class
Anonymous
classes
Method
overloading
Method
overriding
Ans
: c
Packages and interface
1)
What are packages ? what is use of packages ?
Ans
:The package statement defines a name space in which classes are stored.If you
omit the package, the classes are put into the default package.
Signature...
package pkg;
Use:
* It
specifies to which package the classes defined in a file belongs to. * Package
is both naming and a visibility control mechanism.
2)
What is difference between importing "java.applet.Applet" and
"java.applet.*;" ?
Ans
:"java.applet.Applet" will import only the class Applet from the
package java.applet
Where
as "java.applet.*" will import all the classes from java.applet
package.
3)
What do you understand by package access specifier?
Ans
: public: Anything declared as public can be accessed from anywhere
private:
Anything declared in the private can’t be seen outside of its class.
default:
It is visible to subclasses as well as to other classes in the same package.
4)
What is interface? What is use of interface?
Ans
: It is similar to class which may contain method’s signature only but not
bodies.
Methods
declared in interface are abstract methods. We can implement many interfaces on
a class which support the multiple inheritance.
5)
Is it is necessary to implement all methods in an interface?
Ans
: Yes. All the methods have to be implemented.
6)
Which is the default access modifier for an interface method?
Ans
: public.
7)
Can we define a variable in an interface ?and what type it should be ?
Ans
: Yes we can define a variable in an interface. They are implicitly final and
static.
8)
What is difference between interface and an abstract class?
Ans
: All the methods declared inside an Interface are abstract. Where as abstract
class must have at least one abstract method and others may be concrete or
abstract.
In
Interface we need not use the keyword abstract for the methods.
9)
By default, all program import the java.lang package.
True/False
Ans
: True
10)
Java compiler stores the .class files in the path specified in CLASSPATH
environmental
variable.
True/False
Ans
: False
11)
User-defined package can also be imported just like the standard packages.
True/False
Ans
: True
12)
When a program does not want to handle exception, the ______class is used.
Ans
: Throws
13)
The main subclass of the Exception class is _______ class.
Ans
: RuntimeException
14)
Only subclasses of ______class may be caught or thrown.
Ans
: Throwable
15)
Any user-defined exception class is a subclass of the _____ class.
Ans
: Exception
16)
The catch clause of the user-defined exception class should ______ its
Base
class catch clause.
Ans
: Exception
17)
A _______ is used to separate the hierarchy of the class while declaring an
Import
statement.
Ans
: Package
18)
All standard classes of Java are included within a package called _____.
Ans
: java.lang
19)
All the classes in a package can be simultaneously imported using ____.
Ans
: *
20)
Can you define a variable inside an Interface. If no, why? If yes, how?
Ans.:
YES. final and static
21)
How many concrete classes can you have inside an interface?
Ans.:
None
22)
Can you extend an interface?
Ans.:
Yes
23)
Is it necessary to implement all the methods of an interface while implementing
the interface?
Ans.:
No
24)
If you do not implement all the methods of an interface while implementing ,
what specifier should you use for the class ?
Ans.:
abstract
25)
How do you achieve multiple inheritance in Java?
Ans:
Using interfaces.
26)
How to declare an interface example?
Ans
: access class classname implements interface.
27)
Can you achieve multiple interface through interface?
a)True
b)
false
Ans
: a.
28)
Can variables be declared in an interface ? If so, what are the modifiers?
Ans
: Yes. final and static are the modifiers can be declared in an interface.
29)
What are the possible access modifiers when implementing interface methods?
Ans
: public.
30)
Can anonymous classes be implemented an interface?
Ans
: Yes.
31)
Interfaces can’t be extended.
a)True
b)False
Ans
: b.
32)
Name interfaces without a method?
Ans
: Serializable, Cloneble & Remote.
33)
Is it possible to use few methods of an interface in a class ? If so, how?
Ans
: Yes. Declare the class as abstract.
Exception Handling
1)
What is the difference between ‘throw’ and ‘throws’ ?And it’s application?
Ans
: Exceptions that are thrown by java runtime systems can be handled by Try and
catch blocks. With throw exception we can handle the exceptions thrown by the
program itself. If a method is capable of causing an exception that it does not
handle,
it must specify this behavior so the callers of the method can guard
against
that exception.
2)
What is the difference between ‘Exception’ and ‘error’ in java?
Ans
: Exception and Error are the subclasses of the Throwable class. Exception
class is used for exceptional conditions that user program should catch. With
exception class we can subclass to create our own custom exception.
Error
defines exceptions that are not excepted to be caught by you program. Example
is Stack Overflow.
3)
What is ‘Resource leak’?
Ans
: Freeing up other resources that might have been allocated at the beginning of
a method.
4)What
is the ‘finally’ block?
Ans
: Finally block will execute whether or not an exception is thrown. If an
exception is thrown, the finally block will execute even if no catch statement
match the exception. Any time a method is about to return to the caller from
inside try/catch block, via an uncaught exception or an explicit return
statement, the finally clause is also execute.
5)
Can we have catch block with out try block? If so when?
Ans
: No. Try/Catch or Try/finally form a unit.
6)
What is the difference between the following statements?
Catch
(Exception e),
Catch
(Error err),
Catch
(Throwable t)
Ans
:
7)
What will happen to the Exception object after exception handling?
Ans
: It will go for Garbage Collector. And frees the memory.
8)
How many Exceptions we can define in ‘throws’ clause?
Ans
: We can define multiple exceptions in throws clause.
Signature
is..
type
method-name (parameter-list) throws exception-list
9)
The finally block is executed when an exception is thrown, even if no catch
matches it.
True/False
Ans
: True
10)
The subclass exception should precede the base class exception when used within
the catch clause.
True/False
Ans
: True
11)
Exceptions can be caught or rethrown to a calling method.
True/False
Ans
: True
12)
The statements following the throw keyword in a program are not executed.
True/False
Ans
: True
13)
The toString ( ) method in the user-defined exception class is overridden.
True/False
Ans
: True
MULTI THREADING
1)
What are the two types of multitasking?
Ans
: 1.process-based
2.Thread-based
2)
What are the two ways to create the thread?
Ans
: 1.by implementing Runnable
2.by
extending Thread
3)
What is the signature of the constructor of a thread class?
Ans
: Thread(Runnable threadob,String threadName)
4)
What are all the methods available in the Runnable Interface?
Ans
: run()
5)
What is the data type for the method isAlive() and this method is
available
in which class?
Ans
: boolean, Thread
6)
What are all the methods available in the Thread class?
Ans
: 1.isAlive()
2.join()
3.resume()
4.suspend()
5.stop()
6.start()
7.sleep()
8.destroy()
7)
What are all the methods used for Inter Thread communication and what is the
class in which these methods are defined?
Ans
:1. wait(),notify() & notifyall()
2.
Object class
8)
What is the mechanisam defind by java for the Resources to be used by only one
Thread at a time?
Ans
: Synchronisation
9)
What is the procedure to own the moniter by many threads?
Ans
: not possible
10)
What is the unit for 1000 in the below statement?
ob.sleep(1000)
Ans
: long milliseconds
11)
What is the data type for the parameter of the sleep() method?
Ans
: long
12)
What are all the values for the following level?
max-priority
min-priority
normal-priority
Ans
: 10,1,5
13)
What is the method available for setting the priority?
Ans
: setPriority()
14)
What is the default thread at the time of starting the program?
Ans
: main thread
15)
The word synchronized can be used with only a method.
True/
False
Ans
: False
16)
Which priority Thread can prompt the lower primary Thread?
Ans
: Higher Priority
17)
How many threads at a time can access a monitor?
Ans
: one
18)
What are all the four states associated in the thread?
Ans
: 1. new 2. runnable 3. blocked 4. dead
19)
The suspend()method is used to teriminate a thread?
True
/False
Ans
: False
20)
The run() method should necessary exists in clases created as subclass of
thread?
True
/False
Ans
: True
21)
When two threads are waiting on each other and can't proceed the programe is
said to be in a deadlock?
True/False
Ans
: True
22)
Which method waits for the thread to die ?
Ans
: join() method
23)
Which of the following is true?
1)
wait(),notify(),notifyall() are defined as final & can be called only from
with in a synchronized method
2)
Among wait(),notify(),notifyall() the wait() method only throws IOException
3)
wait(),notify(),notifyall() & sleep() are methods of object class
1
2
3
1
& 2
1,2
& 3
Ans
: D
24)
Garbage collector thread belongs to which priority?
Ans
: low-priority
25)
What is meant by timeslicing or time sharing?
Ans
: Timeslicing is the method of allocating CPU time to individual threads in a
priority schedule.
26)
What is meant by daemon thread? In java runtime, what is it's role?
Ans
: Daemon thread is a low priority thread which runs intermittently in the
background doing the garbage collection operation for the java runtime system.
Inheritance
1)
What is the difference between superclass & subclass?
Ans
: A super class is a class that is inherited whereas subclass is a class that
does the inheriting.
2)
Which keyword is used to inherit a class?
Ans
: extends
3)
Subclasses methods can access superclass members/ attributes at all times?
True/False
Ans
: False
4)
When can subclasses not access superclass members?
Ans
: When superclass is declared as private.
5)
Which class does begin Java class hierarchy?
Ans
: Object class
6)
Object class is a superclass of all other classes?
True/False
Ans
: True
7)
Java supports multiple inheritance?
True/False
Ans
: False
8)
What is inheritance?
Ans
: Deriving an object from an existing class. In the other words, Inheritance is
the process of inheriting all the features from a class
9)
What are the advantages of inheritance?
Ans
: Reusability of code and accessibility of variables and methods of the
superclass by subclasses.
10)
Which method is used to call the constructors of the superclass from the
subclass?
Ans
: super(argument)
11)
Which is used to execute any method of the superclass from the subclass?
Ans
: super.method-name(arguments)
12)
Which methods are used to destroy the objects created by the constructor
methods?
Ans
: finalize()
13)
What are abstract classes?
Ans
: Abstract classes are those for which instances can’t be created.
14)
What must a class do to implement an interface?
Ans:
It must provide all of the methods in the interface and identify the interface
in its implements clause.
15)
Which methods in the Object class are declared as final?
Ans
: getClass(), notify(), notifyAll(), and wait()
16)
Final methods can be overridden.
True/False
Ans
: False
17)
Declaration of methods as final results in faster execution of the program?
True/False
Ans:
True
18)
Final variables should be declared in the beginning?
True/False
Ans
: True
19)
Can we declare variable inside a method as final variables? Why?
Ans
: Cannot because, local variable cannot be declared as final variables.
20)
Can an abstract class may be final?
Ans
: An abstract class may not be declared as final.
21)
Does a class inherit the constructors of it's super class?
Ans:
A class does not inherit constructors from any of it's super classes.
22)
What restrictions are placed on method overloading?
Ans:
Two methods may not have the same name and argument list but different return
types.
23)
What restrictions are placed on method overriding?
Ans
: Overridden methods must have the same name , argument list , and return type.
The overriding method may not limit the access of the method it overridees.The
overriding method may not throw any exceptions that may not be thrown by the
overridden method.
24)
What modifiers may be used with an inner class that is a member of an outer
class?
Ans
: a (non-local) inner class may be declared as public, protected, private,
static, final or abstract.
25)
How this() is used with constructors?
Ans:
this() is used to invoke a constructor of the same class
26)
How super() used with constructors?
Ans
: super() is used to invoke a super class constructor
27)
Which of the following statements correctly describes an interface?
a)It's
a concrete class
b)It's
a superclass
c)It's
a type of abstract class
Ans:
c
28)
An interface contains __ methods
a)Non-abstract
b)Implemented
c)unimplemented
Ans:c
STRING HANDLING
Which package does define String and StringBuffer classes?
Ans
: java.lang package.
Which method can be used to obtain the length of the String?
Ans
: length( ) method.
How do you concatenate Strings?
Ans
: By using " + " operator.
Which method can be used to compare two strings for equality?
Ans
: equals( ) method.
Which method can be used to perform a comparison between strings
that ignores case differences?
Ans
: equalsIgnoreCase( ) method.
What is the use of valueOf( ) method?
Ans
: valueOf( ) method converts data from its internal format into a
human-readable form.
What are the uses of toLowerCase( ) and toUpperCase( ) methods?
Ans
: The method toLowerCase( ) converts all the characters in a string from
uppercase to
lowercase.
The
method toUpperCase( ) converts all the characters in a string from lowercase to
uppercase.
Which method can be used to find out the total allocated capacity of
a StrinBuffer?
Ans
: capacity( ) method.
Which method can be used to set the length of the buffer within a
StringBuffer object?
Ans
: setLength( ).
What is the difference between String and StringBuffer?
Ans
: String objects are constants, whereas StringBuffer objects are not.
String
class supports constant strings, whereas StringBuffer class supports growable,
modifiable strings.
What are wrapper classes?
Ans
: Wrapper classes are classes that allow primitive types to be accessed as
objects.
Which of the following is not a wrapper class?
String
Integer
Boolean
Character
Ans
: a.
What is the output of the following program?
public class Question {
public static void main(String args[]) {
String s1 = "abc";
String s2 = "def";
String s3 = s1.concat(s2.toUpperCase( ) );
System.out.println(s1+s2+s3);
}
}
abcdefabcdef
abcabcDEFDEF
abcdefabcDEF
None
of the above
ANS
: c.
Which of the following methods are methods of the String class?
delete(
)
append(
)
reverse(
)
replace(
)
Ans
: d.
Which of the following methods cause the String object referenced by
s to be changed?
s.concat(
)
s.toUpperCase(
)
s.replace(
)
s.valueOf(
)
Ans
: a and b.
String is a wrapper class?
True
False
Ans
: b.
17) If you run the code below, what gets printed out?
String s=new String("Bicycle");
int iBegin=1;
char iEnd=3;
System.out.println(s.substring(iBegin,iEnd));
Bic
ic
c)
icy
d) error: no method matching substring(int,char)
d) error: no method matching substring(int,char)
Ans
: b.
18) Given the following declarations
String s1=new String("Hello")
String s2=new String("there");
String s3=new String();
Which of the following are legal operations?
s3=s1
+ s2;
s3=s1
- s2;
c)
s3=s1 & s2
d) s3=s1 && s2
d) s3=s1 && s2
Ans
: a.
19) Which of the following statements are true?
The
String class is implemented as a char array, elements are addressed using the
stringname[] convention
b)
Strings are a primitive type in Java that overloads the + operator for concatenation
c) Strings are a primitive type in Java and the StringBuffer is used as the matching wrapper type
d) The size of a string can be retrieved using the length property.
c) Strings are a primitive type in Java and the StringBuffer is used as the matching wrapper type
d) The size of a string can be retrieved using the length property.
Ans
: b.
EXPLORING JAVA.LANG
java.lang package is automatically imported into all programs.
True
False
Ans
: a
What are the interfaces defined by java.lang?
Ans
: Cloneable, Comparable and Runnable.
What are the constants defined by both Flaot and Double classes?
Ans
: MAX_VALUE,
MIN_VALUE,
NaN,
POSITIVE_INFINITY,
NEGATIVE_INFINITY
and
TYPE.
What are the constants defined by Byte, Short, Integer and Long?
Ans
: MAX_VALUE,
MIN_VALUE
and
TYPE.
What are the constants defined by both Float and Double classes?
Ans
: MAX_RADIX,
MIN_RADIX,
MAX_VALUE,
MIN_VALUE
and
TYPE.
What is the purpose of the Runtime class?
Ans
: The purpose of the Runtime class is to provide access to the Java runtime
system.
What is the purpose of the System class?
Ans
: The purpose of the System class is to provide access to system resources.
Which class is extended by all other classes?
Ans
: Object class is extended by all other classes.
Which class can be used to obtain design information about an
object?
Ans
: The Class class can be used to obtain information about an object’s design.
Which method is used to calculate the absolute value of a number?
Ans
: abs( ) method.
What are E and PI?
Ans
: E is the base of the natural logarithm and PI is the mathematical value pi.
Which of the following classes is used to perform basic console I/O?
System
SecurityManager
Math
Runtime
Ans
: a.
Which of the following are true?
The
Class class is the superclass of the Object class.
The
Object class is final.
The
Class class can be used to load other classes.
The
ClassLoader class can be used to load other classes.
Ans
: c and d.
Which of the following methods are methods of the Math class?
absolute(
)
log(
)
cosine(
)
sine(
)
Ans
: b.
Which of the following are true about the Error and Exception
classes?
Both
classes extend Throwable.
The
Error class is final and the Exception class is not.
The
Exception class is final and the Error is not.
Both
classes implement Throwable.
Ans
: a.
Which of the following are true?
The
Void class extends the Class class.
The
Float class extends the Double class.
The
System class extends the Runtime class.
The
Integer class extends the Number class.
Ans
: d.
17) Which of the following will output -4.0
System.out.println(Math.floor(-4.7));
System.out.println(Math.round(-4.7));
System.out.println(Math.ceil(-4.7));
d)
System.out.println(Math.Min(-4.7));
Ans
: c.
18) Which of the following are valid statements
a)
public class MyCalc extends Math
b) Math.max(s);
c) Math.round(9.99,1);
d) Math.mod(4,10);
b) Math.max(s);
c) Math.round(9.99,1);
d) Math.mod(4,10);
e)
None of the above.
Ans
: e.
19) What will happen if you attempt to compile and run the following
code?
Integer ten=new Integer(10);
Long nine=new Long (9);
System.out.println(ten + nine);
int i=1;
System.out.println(i + ten);
19
followed by 20
19
followed by 11
Error:
Can't convert java lang Integer
d)
10 followed by 1
Ans
: c.
INPUT / OUTPUT : EXPLORING JAVA.IO
What is meant by Stream and what are the types of Streams and
classes of the Streams?
Ans
: A Stream is an abstraction that either produces or consumes information.
There
are two types of Streams. They are:
Byte
Streams :
Byte Streams provide a convenient means for handling input and output of bytes.
Character
Streams :
Character Streams provide a convenient means for handling input and output of
characters.
Byte
Stream classes : Byte Streams are defined by using two abstract classes. They
are:InputStream and OutputStream.
Character
Stream classes
: Character Streams are defined by using two abstract classes. They are :
Reader and Writer.
Which of the following statements are true?
UTF
characters are all 8-bits.
UTF
characters are all 16-bits.
UTF
characters are all 24-bits.
Unicode
characters are all 16-bits.
Bytecode
characters are all 16-bits.
Ans
: d.
Which of the following statements are true?
When
you construct an instance of File, if you do not use the filenaming semantics
of the local machine, the constructor will throw an IOException.
When
you construct an instance of File, if the corresponding file does not exist on
the local file system, one will be created.
When
an instance of File is garbage collected, the corresponding file on the local
file system is deleted.
None
of the above.
Ans
: a,b and c.
The File class contains a method that changes the current working
directory.
True
False
Ans
: b.
It is possible to use the File class to list the contents of the
current working
directory.
True
False
Ans
: a.
Readers have methods that can read and return floats and doubles.
True
False
Ans
: b.
You execute the code below in an empty directory. What is the
result?
File
f1 = new File("dirname");
File
f2 = new File(f1, "filename");
A
new directory called dirname is created in the current working directory.
A
new directory called dirname is created in the current working directory. A new
file called filename is created in directory dirname.
A
new directory called dirname and a new file called filename are created, both
in the current working directory.
A
new file called filename is created in the current working directory.
No
directory is created, and no file is created.
Ans
: e.
What is the difference between the Reader/Writer class hierarchy and
the
InputStream/OutputStream class hierarchy?
Ans
: The Reader/Writer class hierarchy is character-oriented and the
InputStream/OutputStream class hierarchy is byte-oriented.
What is an I/O filter?
Ans
: An I/O filter is an object that reads from one stream and writes to another,
usually altering the data in some way as it is passed from one stream to
another.
What is the purpose of the File class?
Ans
: The File class is used to create objects that provide access to the files and
directories of a local file system.
What interface must an object implement before it can be written to
a stream as an object?
Ans
: An object must implement the Serializable or Externalizable interface before it
can be written to a stream as an object.
What is the difference between the File and RandomAccessFile
classes?
Ans
: The File class encapsulates the files and directories of the local file
system. The RandomAccessFile class provides the methods needed to directly
access data contained in any part of a file.
What class allows you to read objects directly from a stream?
Ans
: The ObjectInputStream class supports the reading of objects from input
streams.
What value does read( ) return when it has reached the end of a
file?
Ans
: The read( ) method returns – 1 when it has reached the end of a file.
What value does readLine( ) return when it has reached the end of a
file?
Ans
: The readLine( ) method returns null when it has reached the end of a
file.
How many bits are used to represent Unicode, ASCII, UTF-16 and UTF-8
characters?
Ans
: Unicode requires 16-bits and ASCII requires 8-bits. Although the ASCII
character set uses only 1-bits, it is usually represented as 8-bits. UTF-8
represents characters using 8, 16 and 18-bit patterns. UTF-16 uses 16-bit and
larger bit patterns.
Which of the following are true?
The
InputStream and OutputStream classes are byte-oriented.
The
ObjectInputStream and ObjectOutputStream do not support serialized object input
and output.
The
Reader and Writer classes are character-oriented.
The
Reader and Writer classes are the preferred solution to serialized object
output.
Ans
: a and c.
Which of the following are true about I/O filters?
Filters
are supported on input, but not on output.
Filters
are supported by the InputStream/OutputStream class hierarchy, but not by the
Reader/Writer class hierarchy.
Filters
read from one stream and write to another.
A
filter may alter data that is read from one stream and written to another.
Ans
: c and d.
Which of the following are true?
Any
Unicode character is represented using 16-bits.
7-bits
are needed to represent any ASCII character.
UTF-8
characters are represented using only 8-bits.
UTF-16
characters are represented using only 16-bits.
Ans
: a and b.
Which of the following are true?
The
Serializable interface is used to identify objects that may be written to an
output stream.
The
Externalizable interface is implemented by classes that control the way in
which their objects are serialized.
The
Serializable interface extends the Externalizable interface.
The
Externalizable interface extends the Serializable interface.
Ans
: a, b and d.
Which of the following are true about the File class?
A
File object can be used to change the current working directory.
A
File object can be used to access the files in the current directory.
When
a File object is created, a corresponding directory or file is created in the
local file system.
File
objects are used to access files and directories on the local file system.
File
objects can be garbage collected.
When
a File object is garbage collected, the corresponding file or directory is
deleted.
Ans
: b, d and e.
How do you create a Reader object from an InputStream object?
Use
the static createReader( ) method of InputStream class.
Use
the static createReader( ) method of Reader class.
Create
an InputStreamReader object, passing the InputStream object as an argument to
the InputStreamReader constructor.
Create
an OutputStreamReader object, passing the InputStream object as an argument to
the OutputStreamReader constructor.
Ans
: c.
Which of the following are true?
Writer
classes can be used to write characters to output streams using different
character encodings.
Writer
classes can be used to write Unicode characters to output streams.
Writer
classes have methods that support the writing of the values of any Java
primitive type to output streams.
Writer
classes have methods that support the writing of objects to output streams.
Ans
: a and b.
The isFile( ) method returns a boolean value depending on whether
the file object is a file or a directory.
True.
False.
Ans
: a.
Reading or writing can be done even after closing the input/output
source.
True.
False.
Ans
: b.
The ________ method helps in clearing the buffer.
Ans
: flush( ).
The System.err method is used to print error message.
True.
False.
Ans
: a.
What is meant by StreamTokenizer?
Ans
: StreamTokenizer breaks up InputStream into tokens that are delimited by sets
of characters.
It
has the constructor : StreamTokenizer(Reader inStream).
Here
inStream must be some form of Reader.
What is Serialization and deserialization?
Ans
: Serialization is the process of writing the state of an object to a byte
stream.
Deserialization
is the process of restoring these objects.
30) Which of the following can you perform using the File class?
a)
Change the current directory
b) Return the name of the parent directory
c) Delete a file
d) Find if a file contains text or binary information
b) Return the name of the parent directory
c) Delete a file
d) Find if a file contains text or binary information
Ans
: b and c.
31)How can you change the current working directory using an
instance of the File class called FileName?
FileName.chdir("DirName").
FileName.cd("DirName").
FileName.cwd("DirName").
The
File class does not support directly changing the current directory.
Ans
: d.
EVENT HANDLING
The event delegation model, introduced in release 1.1 of the JDK, is
fully compatible with the
event model.
True
False
Ans
: b.
A component subclass that has executed enableEvents( ) to enable
processing of a certain kind of event cannot also use an adapter as a listener
for the same kind of event.
True
False
Ans
: b.
What is the highest-level event class of the event-delegation model?
Ans
: The java.util.eventObject class is the highest-level class in the
event-delegation hierarchy.
What interface is extended by AWT event listeners?
Ans
: All AWT event listeners extend the java.util.EventListener interface.
What class is the top of the AWT event hierarchy?
Ans
: The java.awt.AWTEvent class is the highest-level class in the AWT event class
hierarchy.
What event results from the clicking of a button?
Ans
: The ActionEvent event is generated as the result of the clicking of a button.
What is the relationship between an event-listener interface and an
event-adapter class?
Ans
: An event-listener interface defines the methods that must be implemented by
an event
handler
for a particular kind of event.
An
event adapter provides a default implementation of an event-listener interface.
In which package are most of the AWT events that support the
event-delegation model defined?
Ans
: Most of the AWT–related events of the event-delegation model are defined in
the
java.awt.event
package. The AWTEvent class is defined in the java.awt package.
What is the advantage of the event-delegation model over the earlier
event-inheritance model?
Ans
: The event-delegation has two advantages over the event-inheritance model.
They are :
It
enables event handling by objects other than the ones that generate the events.
This
allows
a clean separation between a component’s design and its use.
It
performs much better in applications where many events are generated. This
performance
improvement is due to the fact that the event-delegation model does not
have
to repeatedly process unhandled events, as is the case of the event-inheritance
model.
What is the purpose of the enableEvents( ) method?
Ans
:The enableEvents( ) method is used to enable an event for a particular object.
Which of the following are true?
The
event-inheritance model has replaced the event-delegation model.
The
event-inheritance model is more efficient than the event-delegation model.
The
event-delegation model uses event listeners to define the methods of event-handling
classes.
The
event-delegation model uses the handleEvent( ) method to support event
handling.
Ans
: c.
Which of the following is the highest class in the event-delegation
model?
java.util.EventListener
java.util.EventObject
java.awt.AWTEvent
java.awt.event.AWTEvent
Ans
: b.
When two or more objects are added as listeners for the same event,
which listener is first invoked to handle the event?
The
first object that was added as listener.
The
last object that was added as listener.
There
is no way to determine which listener will be invoked first.
It
is impossible to have more than one listener for a given event.
Ans
: c.
Which of the following components generate action events?
Buttons
Labels
Check
boxes
Windows
Ans
: a.
Which of the following are true?
A
TextField object may generate an ActionEvent.
A
TextArea object may generate an ActionEvent.
A
Button object may generate an ActionEvent.
A
MenuItem object may generate an ActionEvent.
Ans
: a,c and d.
Which of the following are true?
The
MouseListener interface defines methods for handling mouse clicks.
The
MouseMotionListener interface defines methods for handling mouse clicks.
The
MouseClickListener interface defines methods for handling mouse clicks.
The
ActionListener interface defines methods for handling the clicking of a button.
Ans
: a and d.
Suppose that you want to have an object eh handle the TextEvent of a
TextArea object t. How should you add eh as the event handler for t?
t.addTextListener(eh);
eh.addTextListener(t);
addTextListener(eh.t);
addTextListener(t,eh);
Ans
: a.
What is the preferred way to handle an object’s events in Java 2?
Override
the object’s handleEvent( ) method.
Add
one or more event listeners to handle the events.
Have
the object override its processEvent( ) methods.
Have
the object override its dispatchEvent( ) methods.
Ans
: b.
Which of the following are true?
A
component may handle its own events by adding itself as an event listener.
A
component may handle its own events by overriding its event-dispatching method.
A
component may not handle oits own events.
A
component may handle its own events only if it implements the handleEvent( )
method.
Ans
: a and b.
APPLETS
What is an Applet? Should applets have constructors?
Ans
: Applet is a dynamic and interactive program that runs inside a Web page
displayed
by a Java capable browser. We don’t have the concept of Constructors in
Applets.
How do we read number information from my applet’s parameters, given
that Applet’s getParameter() method returns a string?
Ans
: Use the parseInt() method in the Integer Class, the Float(String) constructor
in the
Class
Float, or the Double(String) constructor in the class Double.
How can I arrange for different applets on a web page to communicate
with each other?
Ans
: Name your applets inside the Applet tag and invoke AppletContext’s
getApplet()
method
in your applet code to obtain references to the other applets on the page.
How do I select a URL from my Applet and send the browser to that
page?
Ans
: Ask the applet for its applet context and invoke showDocument() on that
context object.
Eg.
URL targetURL;
String
URLString
AppletContext
context = getAppletContext();
try{
targetUR
L = new URL(URLString);
}
catch (Malformed URLException e){
//
Code for recover from the exception
}
context.
showDocument (targetURL);
Can applets on different pages communicate with each other?
Ans
: No. Not Directly. The applets will exchange the information at one meeting
place
either
on the local file system or at remote system.
How do Applets differ from Applications?
Ans
: Appln: Stand Alone
Applet:
Needs no explicit installation on local m/c.
Appln:
Execution starts with main() method.
Applet:
Execution starts with init() method.
Appln:
May or may not be a GUI
Applet:
Must run within a GUI (Using AWT)
How do I determine the width and height of my application?
Ans
: Use the getSize() method, which the Applet class inherits from the Component
class
in the Java.awt package. The getSize() method returns the size of the applet as
a
Dimension object, from which you extract separate width, height fields.
Eg.
Dimension dim = getSize ();
int
appletwidth = dim.width ();
8) What is AppletStub Interface?
Ans
: The applet stub interface provides the means by which an applet and the
browser communicate. Your code will not typically implement this interface.
It is essential to have both the .java file and the .html file of an
applet in the
same
directory.
True.
False.
Ans
: b.
The <PARAM> tag contains two attributes namely _________ and
_______.
Ans
: Name , value.
Passing values to parameters is done in the _________ file of an
applet.
Ans
: .html.
12) What tags are mandatory when creating HTML to display an applet
name,
height, width
code,
name
codebase,
height, width
d)
code, height, width
Ans
: d.
Applet’s getParameter( ) method can be used to get parameter values.
True.
False.
Ans
: a.
What are the Applet’s Life Cycle methods? Explain them?
Ans
: init( ) method - Can be called when an applet is first loaded.
start(
) method - Can be called each time an applet is started.
paint(
) method - Can be called when the applet is minimized or refreshed.
stop(
) method - Can be called when the browser moves off the applet’s page.
destroy(
) method - Can be called when the browser is finished with the applet.
What are the Applet’s information methods?
Ans
: getAppletInfo( ) method : Returns a string describing the applet, its author
,copy
right
information, etc.
getParameterInfo(
) method : Returns an array of string describing the applet’s parameters.
All Applets are subclasses of Applet.
True.
False.
Ans
: a.
All Applets must import java.applet and java.awt.
True.
False.
Ans
: a.
What are the steps involved in Applet development?
Ans
: a) Edit a Java source file,
b)
Compile your program and
c)
Execute the appletviewer, specifying the name of your applet’s source file.
Applets are executed by the console based Java run-time interpreter.
True.
False.
Ans
: b.
Which classes and interfaces does Applet class consist?
Ans
: Applet class consists of a single class, the Applet class and three
interfaces: AppletContext,
AppletStub
and AudioClip.
What is the sequence for calling the methods by AWT for applets?
Ans
: When an applet begins, the AWT calls the following methods, in this sequence.
init(
)
start(
)
paint(
)
When
an applet is terminated, the following sequence of method cals takes place :
stop(
)
destroy(
)
Which method is used to output a string to an applet?
Ans
: drawString ( ) method.
Every color is created from an RGB value.
True.
False
Ans
: a.
AWT
: WINDOWS, GRAPHICS AND FONTS
How would you set the color of a graphics context called g to cyan?
g.setColor(Color.cyan);
g.setCurrentColor(cyan);
g.setColor("Color.cyan");
g.setColor("cyan’);
g.setColor(new
Color(cyan));
Ans
: a.
The code below draws a line. What color is the line?
g.setColor(Color.red.green.yellow.red.cyan);
g.drawLine(0, 0, 100,100);
Red
Green
Yellow
Cyan
Black
Ans
: d.
What does the following code draw?
g.setColor(Color.black);
g.drawLine(10, 10, 10, 50);
g.setColor(Color.RED);
g.drawRect(100, 100, 150, 150);
A
red vertical line that is 40 pixels long and a red square with sides of 150
pixels
A
black vertical line that is 40 pixels long and a red square with sides of 150
pixels
A
black vertical line that is 50 pixels long and a red square with sides of 150
pixels
A
red vertical line that is 50 pixels long and a red square with sides of 150
pixels
A
black vertical line that is 40 pixels long and a red square with sides of 100
pixel
Ans
: b.
Which of the statements below are true?
A
polyline is always filled.
b)
A polyline can not be filled.
c)
A polygon is always filled.
d)
A polygon is always closed
e)
A polygon may be filled or not filled
Ans
: b, d and e.
What code would you use to construct a 24-point bold serif font?
new
Font(Font.SERIF, 24,Font.BOLD);
new
Font("SERIF", 24, BOLD");
new
Font("BOLD ", 24,Font.SERIF);
new
Font("SERIF", Font.BOLD,24);
new
Font(Font.SERIF, "BOLD", 24);
Ans
: d.
What does the following paint( ) method draw?
Public void paint(Graphics g) {
g.drawString("question #6",10,0);
}
The
string "question #6", with its top-left corner at 10,0
A
little squiggle coming down from the top of the component, a little way in from
the left edge
Ans
: b.
What does the following paint( ) method draw?
Public void paint(Graphics g) {
g.drawString("question #6",10,0);
}
A
circle at (100, 100) with radius of 44
A
circle at (100, 44) with radius of 100
A
circle at (100, 44) with radius of 44
The
code does not compile
Ans
: d.
8)What is relationship between the Canvas class and the Graphics
class?
Ans
: A Canvas object provides access to a Graphics object via its paint( ) method.
What are the Component subclasses that support painting.
Ans
: The Canvas, Frame, Panel and Applet classes support painting.
What is the difference between the paint( ) and repaint( ) method?
Ans
: The paint( ) method supports painting via a Graphics object. The repaint( )
method is used
to
cause paint( ) to be invoked by the AWT painting method.
What is the difference between the Font and FontMetrics classes?
Ans
: The FontMetrics class is used to define implementation-specific properties,
such as ascent
and
descent, of a Font object.
Which of the following are passed as an argument to the paint( )
method?
A
Canvas object
A
Graphics object
An
Image object
A
paint object
Ans
: b.
Which of the following methods are invoked by the AWT to support
paint and repaint operations?
paint(
)
repaint(
)
draw(
)
redraw(
)
Ans
: a.
Which of the following classes have a paint( ) method?
Canvas
Image
Frame
Graphics
Ans
: a and c.
Which of the following are methods of the Graphics class?
drawRect(
)
drawImage(
)
drawPoint(
)
drawString(
)
Ans
: a, b and d.
Which Font attributes are available through the FontMetrics class?
ascent
leading
case
height
Ans
: a, b and d.
Which of the following are true?
The
AWT automatically causes a window to be repainted when a portion of a window
has been minimized and then maximized.
The
AWT automatically causes a window to be repainted when a portion of a window
has been covered and then uncovered.
The
AWT automatically causes a window to be repainted when application data is
changed.
The
AWT does not support repainting operations.
Ans
: a and b.
Which method is used to size a graphics object to fit the current
size of the window?
Ans
: getSize( ) method.
What are the methods to be used to set foreground and background
colors?
Ans
: setForeground( ) and setBackground( ) methods.
19) You have created a simple Frame and overridden the paint method
as follows
public void paint(Graphics g){
g.drawString("Dolly",50,10);
}
What will be the result when you attempt to compile and run the
program?
The
string "Dolly" will be displayed at the centre of the frame
b)
An error at compilation complaining at the signature of the paint method
c) The lower part of the word Dolly will be seen at the top of the form, with the top hidden.
d) The string "Dolly" will be shown at the bottom of the form
c) The lower part of the word Dolly will be seen at the top of the form, with the top hidden.
d) The string "Dolly" will be shown at the bottom of the form
Ans
: c.
20) Where g is a graphics instance what will the following code draw
on the screen.
g.fillArc(45,90,50,50,90,180);
a)
An arc bounded by a box of height 45, width 90 with a centre point of 50,50,
starting
at an angle of 90 degrees traversing through 180 degrees counter clockwise.
at an angle of 90 degrees traversing through 180 degrees counter clockwise.
b)
An arc bounded by a box of height 50, width 50, with a centre point of 45,90
starting
at an angle of 90 degrees traversing through 180 degrees clockwise.
at an angle of 90 degrees traversing through 180 degrees clockwise.
c)
An arc bounded by a box of height 50, width 50, with a top left at coordinates
of 45,
90, starting at 90 degrees and traversing through 180 degrees counter clockwise.
90, starting at 90 degrees and traversing through 180 degrees counter clockwise.
d)
An arc starting at 45 degrees, traversing through 90 degrees clockwise bounded
by a
box of height 50, width 50 with a centre point of 90, 180.
box of height 50, width 50 with a centre point of 90, 180.
Ans
: c.
21) Given the following code
import java.awt.*;
public class SetF extends Frame{
public static void main(String argv[]){
SetF s = new SetF();
s.setSize(300,200);
s.setVisible(true);
}
}
How could you set the frame surface color to pink
import java.awt.*;
public class SetF extends Frame{
public static void main(String argv[]){
SetF s = new SetF();
s.setSize(300,200);
s.setVisible(true);
}
}
How could you set the frame surface color to pink
a)s.setBackground(Color.pink);
b)s.setColor(PINK);
c)s.Background(pink);
d)s.color=Color.pink
b)s.setColor(PINK);
c)s.Background(pink);
d)s.color=Color.pink
Ans
: a.
AWT:
CONTROLS, LAYOUT MANAGERS AND MENUS
What is meant by Controls and what are different types of controls?
Ans
: Controls are componenets that allow a user to interact with your application.
The
AWT supports the following types of controls:
Labels
Push
buttons
Check
boxes
Choice
lists
Lists
Scroll
bars
Text
components
These
controls are subclasses of Component.
You want to construct a text area that is 80 character-widths wide
and 10 character-heights tall. What code do you use?
new
TextArea(80, 10)
new
TextArea(10, 80)
Ans:
b.
A text field has a variable-width font. It is constructed by calling
new
TextField("iiiii"). What happens if you change the
contents of the text field to
"wwwww"? (Bear in mind that is one of the narrowest
characters, and w is one of the widest.)
The
text field becomes wider.
The
text field becomes narrower.
The
text field stays the same width; to see the entire contents you will have to
scroll by using the ß and à keys.
The
text field stays the same width; to see the entire contents you will have to
scroll by using the text field’s horizontal scroll bar.
Ans
: c.
The CheckboxGroup class is a subclass of the Component class.
True
False
Ans
: b.
5) What are the immediate super classes of the following classes?
a)
Container class
b)
MenuComponent class
c)
Dialog class
d)
Applet class
e)
Menu class
Ans
: a) Container - Component
b)
MenuComponent - Object
c)
Dialog - Window
d)
Applet - Panel
e)
Menu - MenuItem
6) What are the SubClass of Textcomponent Class?
Ans
: TextField and TextArea
7) Which method of the component class is used to set the position
and the size of a component?
Ans
: setBounds()
8) Which TextComponent method is used to set a TextComponent to the
read-only state?
Ans
: setEditable()
9) How can the Checkbox class be used to create a radio button?
Ans
: By associating Checkbox objects with a CheckboxGroup.
10) What Checkbox method allows you to tell if a Checkbox is checked?
Ans
: getState()
11) Which Component method is used to access a component's immediate
Container?
getVisible()
getImmediate
getParent()
getContainer
Ans
: c.
12) What methods are used to get and set the text label displayed by
a Button object?
Ans
: getLabel( ) and setLabel( )
13) What is the difference between a Choice and a List?
Ans
: A Choice is displayed in a compact form that requires you to pull it down to
see the list of available choices. Only one item may be selected from a Choice.
A
List may be displayed in such a way that several List items are visible. A List
supports the selection of one or more List items.
14) Which Container method is used to cause a container to be laid
out and redisplayed?
Ans
: validate( )
15) What is the difference between a Scollbar and a Scrollpane?
Ans
: A Scrollbar is a Component, but not a Container.
A
Scrollpane is a Container and handles its own events and performs its own
scrolling.
16) Which Component subclass is used for drawing and painting?
Ans
: Canvas.
17) Which of the following are direct or indirect subclasses of
Component?
Button
Label
CheckboxMenuItem
Toolbar
Frame
Ans
: a, b and e.
18) Which of the following are direct or indirect subclasses of
Container?
Frame
TextArea
MenuBar
FileDialog
Applet
Ans
: a,d and e.
19) Which method is used to set the text of a Label object?
setText(
)
setLabel(
)
setTextLabel(
)
setLabelText(
)
Ans
: a.
20) Which constructor creates a TextArea with 10 rows and 20
columns?
new
TextArea(10, 20)
new
TextArea(20, 10)
new
TextArea(new Rows(10), new columns(20))
new
TextArea(200)
Ans
: a.
(Usage
is TextArea(rows, columns)
21) Which of the following creates a List with 5 visible items and
multiple selection enabled?
new
List(5, true)
new
List(true, 5)
new
List(5, false)
new
List(false,5)
Ans
: a.
[Usage
is List(rows, multipleMode)]
22) Which are true about the Container class?
The
validate( ) method is used to cause a Container to be laid out and redisplayed.
The
add( ) method is used to add a Component to a Container.
The
getBorder( ) method returns information about a Container’s insets.
The
getComponent( ) method is used to access a Component that is contained in a
Container.
Ans
: a, b and d.
23) Suppose a Panel is added to a Frame and a Button is added to the
Panel. If the Frame’s font is set to 12-point TimesRoman, the Panel’s font is
set to 10-point TimesRoman, and the Button’s font is not set, what font will be
used to dispaly the Button’s label?
12-point
TimesRoman
11-point
TimesRoman
10-point
TimesRoman
9-point
TimesRoman
Ans
: c.
A Frame’s background color is set to Color.Yellow, and a Button’s
background color is to Color.Blue. Suppose the Button is added to a Panel,
which is added to the Frame. What background color will be used with the Panel?
Colr.Yellow
Color.Blue
Color.Green
Color.White
Ans
: a.
25) Which method will cause a Frame to be displayed?
show(
)
setVisible(
)
display(
)
displayFrame(
)
Ans
: a and b.
26) All the componenet classes and container classes are derived
from _________ class.
Ans
: Object.
27) Which method of the container class can be used to add
components to a Panel.
Ans
: add ( ) method.
28) What are the subclasses of the Container class?
Ans
: The Container class has three major subclasses. They are :
Window
Panel
ScrollPane
29) The Choice component allows multiple selection.
True.
False.
Ans
: b.
30) The List component does not generate any events.
True.
False.
Ans
: b.
31) Which components are used to get text input from the user.
Ans
: TextField and TextArea.
32) Which object is needed to group Checkboxes to make them
exclusive?
Ans
: CheckboxGroup.
33) Which of the following components allow multiple selections?
Non-exclusive
Checkboxes.
Radio
buttons.
Choice.
List.
Ans
: a and d.
34) What are the types of Checkboxes and what is the difference
between them?
Ans
: Java supports two types of Checkboxes. They are : Exclusive and
Non-exclusive.
In
case of exclusive Checkboxes, only one among a group of items can be selected
at a time. I f an item from the group is selected, the checkbox currently
checked is deselected and the new selection is highlighted. The exclusive
Checkboxes are also called as Radio buttons.
The
non-exclusive checkboxes are not grouped together and each one can be selected
independent of the other.
35) What is a Layout Manager and what are the different Layout
Managers available in java.awt and what is the default Layout manager for the
panal and the panal subclasses?
Ans:
A layout Manager is an object that is used to organize components in a
container.
The
different layouts available in java.awt are :
FlowLayout,
BorderLayout, CardLayout, GridLayout and GridBag Layout.
The
default Layout Manager of Panal and Panal sub classes is FlowLayout".
36) Can I exert control over the size and placement of components in
my interface?
Ans
: Yes.
myPanal.setLayout(null);
myPanal.setbounds(20,20,200,200);
37) Can I add the same component to more than one container?
Ans
: No. Adding a component to a container automatically removes it from any previous
parent(container).
38) How do I specify where a window is to be placed?
Ans
: Use setBounds, setSize, or setLocation methods to implement this.
setBounds(int
x, int y, int width, int height)
setBounds(Rectangle
r)
setSize(int
width, int height)
setSize(Dimension
d)
setLocation(int
x, int y)
setLocation(Point
p)
39) How can we create a borderless window?
Ans
: Create an instance of the Window class, give it a size, and show it on the
screen.
eg.
Frame aFrame = ......
Window
aWindow = new Window(aFrame);
aWindow.setLayout(new
FlowLayout());
aWindow.add(new
Button("Press Me"));
aWindow.getBounds(50,50,200,200);
aWindow.show();
40) Can I create a non-resizable windows? If so, how?
Ans:
Yes. By using setResizable() method in class Frame.
41) What is the default Layout Manager for the Window and Window
subclasses (Frame,Dialog)?
Ans
: BorderLayout().
42) How are the elements of different layouts organized?
Ans
: FlowLayout : The elements of a FlowLayout are organized in a top to
bottom, left to right fashion.
BorderLayout
: The
elements of a BorderLayout are organized at the
borders
(North, South, East and West) and the center of a
container.
CardLayout
: The
elements of a CardLayout are stacked, one on top of the other, like a deck of
cards.
GridLayout
: The
elements of a GridLayout are of equal size and are laid out using the square of
a grid.
GridBagLayout
: The
elements of a GridBagLayout are organized according to a grid.However, the
elements are of different sizes and may occupy
more
than one row or column of the grid. In addition, the rows and columns may have
different sizes.
43) Which containers use a BorderLayout as their default layout?
Ans
: The Window, Frame and Dialog classes use a BorderLayout as their default
layout.
44) Which containers use a FlowLayout as their default layout?
Ans
: The Panel and the Applet classes use the FlowLayout as their default layout.
45) What is the preferred size of a component?
Ans
: The preferred size of a component size that will allow the component to
display normally.
46) Which method is method to set the layout of a container?
startLayout(
)
initLayout(
)
layoutContainer(
)
setLayout(
)
Ans
: d.
47) Which method returns the preferred size of a component?
getPreferredSize(
)
getPreferred(
)
getRequiredSize(
)
getLayout(
)
Ans
: a.
48) Which layout should you use to organize the components of a
container in a
tabular form?
CardLayout
BorederLayout
FlowLayout
GridLayout
Ans
: d.
An application has a frame that uses a Border layout manager. Why is
it probably not a good idea to put a vertical scroll bar at North in the frame?
The
scroll bar’s height would be its preferred height, which is not likely to be
enough.
The
scroll bar’s width would be the entire width of the frame, which would be much
wider than necessary.
Both
a and b.
Neither
a nor b. There is no problem with the layout as described.
Ans
: c.
What is the default layouts for a applet, a frame and a panel?
Ans
: For an applet and a panel, Flow layout is the default layout, whereas Border
layout is default layout for a frame.
If a frame uses a Grid layout manager and does not contain any
panels, then all the components within the frame are the same width and height.
True
False.
Ans
: a.
If a frame uses its default layout manager and does not contain any
panels, then all the components within the frame are the same width and height.
True
False.
Ans
: b.
With a Border layout manager, the component at Center gets all the
space that is left over, after the components at North and South have been
considered.
True
False
Ans
: b.
An Applet has its Layout Manager set to the default of FlowLayout.
What code would be the correct to change to another Layout Manager?
setLayoutManager(new
GridLayout());
setLayout(new
GridLayout(2,2));
c)
setGridLayout(2,2,))
d setBorderLayout();
d setBorderLayout();
Ans
: b.
55) How do you indicate where a component will be positioned using
Flowlayout?
a)
North, South,East,West
b) Assign a row/column grid reference
c) Pass a X/Y percentage parameter to the add method
d) Do nothing, the FlowLayout will position the component
b) Assign a row/column grid reference
c) Pass a X/Y percentage parameter to the add method
d) Do nothing, the FlowLayout will position the component
Ans
:d.
56) How do you change the current layout manager for a container?
a)
Use the setLayout method
b) Once created you cannot change the current layout manager of a component
c) Use the setLayoutManager method
d) Use the updateLayout method
b) Once created you cannot change the current layout manager of a component
c) Use the setLayoutManager method
d) Use the updateLayout method
Ans
:a.
57)When using the GridBagLayout manager, each new component requires
a new instance of the GridBagConstraints class. Is this statement true or
false?
a)
true
b) false
b) false
Ans
: b.
58) Which of the following statements are true?
a)The
default layout manager for an Applet is FlowLayout
b) The default layout manager for an application is FlowLayout
c) A layout manager must be assigned to an Applet before the setSize method is called
d) The FlowLayout manager attempts to honor the preferred size of any components
b) The default layout manager for an application is FlowLayout
c) A layout manager must be assigned to an Applet before the setSize method is called
d) The FlowLayout manager attempts to honor the preferred size of any components
Ans
: a and d.
59) Which method does display the messages whenever there is an item
selection or deselection of the CheckboxMenuItem menu?
Ans
: itemStateChanged method.
60) Which is a dual state menu item?
Ans
: CheckboxMenuItem.
61) Which method can be used to enable/diable a checkbox menu item?
Ans
: setState(boolean).
Which of the following may a menu contain?
A
separator
A
check box
A
menu
A
button
A
panel
Ans
: a and c.
Which of the following may contain a menu bar?
A
panel
A
frame
An
applet
A
menu bar
A
menu
Ans
: b
64) What is the difference between a MenuItem and a
CheckboxMenuItem?
Ans
: The CheckboxMenuItem class extends the MenuItem class to support a menu item
that
may be checked or unchecked.
65) Which of the following are true?
A
Dialog can have a MenuBar.
MenuItem
extends Menu.
A
MenuItem can be added to a Menu.
A
Menu can be added to a Menu.
Ans
: c and d.
Which colour is used to indicate instance methods in the standard
"javadoc" format documentation:
1)
blue
2)
red
3)
purple
4)
orange
Answer : 2
explain
In
JDK 1.1 the variabels, methods and constructors are colour coded to
simplifytheir identification.
endExplain
What
is the correct ordering for the import, class and package declarations when
found in a single file?
1)
package, import, class
2)
class, import, package
3)
import, package, class
4)
package, class, import
Answer : 1
explain
This
is my explanation for question 2
endExplain
Which
methods can be legally applied to a string object?
(Multiple)
1)
equals(String)
2)
equals(Object)
3)
trim()
4)
round()
5)
toString()
Answer : 1,2,3,5
What
is the parameter specification for the public static void main method?
(multiple)
1)
String args []
2)
String [] args
3)
Strings args []
4)
String args
Answer : 1,2
What
does the zeroth element of the string array passed to the public static void
main method contain?
(multiple)
1)
The name of the program
2)
The number of arguments
3)
The first argument if one is present
Answer : 3
Which
of the following are Java keywords?
(multiple)
1)
goto
2)
malloc
3)
extends
4)
FALSE
Answer : 3
What
will be the result of compiling the following code:
public class Test {
public static void main (String args []) {
int age;
age = age + 1;
System.out.println("The age is " + age);
}
}
1)
Compiles and runs with no output
2)
Compiles and runs printing out The age is 1
3)
Compiles but generates a runtime error
4)
Does not compile
5)
Compiles but generates a compile time error
Answer : 4
Which
of these is the correct format to use to create the literal char value a?
(multiple)
1)
'a'
2)
"a"
3)
new Character(a)
4)
\000a
Answer : 1
What
is the legal range of a byte integral type?
1)
0 - 65, 535
2)
(-128) - 127
3)
(-32,768) - 32,767
4)
(-256) - 255
Answer : 2
Which
of the following is illegal:
1)
int i = 32;
2)
float f = 45.0;
3)
double d = 45.0;
Answer
2
What
will be the result of compiling the following code:
public class Test {
static int age;
public static void main (String args []) {
age = age + 1;
System.out.println("The age is " + age);
}
}
1)
Compiles and runs with no output
2)
Compiles and runs printing out The age is 1
3)
Compiles but generates a runtime error
4)
Does not compile
5)
Compiles but generates a compile time error
Answer : 2
Which
of the following are correct?
(multiple)
1)
128 >> 1 gives 64
2)
128 >>> 1 gives 64
3)
128 >> 1 gives -64
4)
128 >>> 1 gives -64
Answer : 1
Which
of the following return true?
(multiple)
1)
"john" == new String("john")
2)
"john".equals("john")
3)
"john" = "john"
4)
"john".equals(new Button("john"))
Answer : 2
Which
of the following do not lead to a runtime error?
(multiple)
1)
"john" + " was " + " here"
2)
"john" + 3
3)
3 + 5
4)
5 + 5.5
answer
1,2,3,4
Which
of the following are so called "short circuit" logical operators?
(multiple)
1)
&
2)
||
3)
&&
4)
|
Answer : 2,3
Which
of the following are acceptable?
(multiple)
1)
Object o = new Button("A");
2)
Boolean flag = true;
3)
Panel p = new Frame();
4)
Frame f = new Panel();
5)
Panel p = new Applet();
Answer : 1,5
What
is the result of compiling and running the following code:
public class Test {
static int total = 10;
public static void main (String args []) {
new Test();
}
public Test () {
System.out.println("In test");
System.out.println(this);
int temp = this.total;
if (temp > 5) {
System.out.println(temp);
}
}
}
(multiple)
1)
The class will not compile
2)
The compiler reports and error at line 2
3)
The compiler reports an error at line 9
4)
The value 10 is one of the elements printed to the standard output
5)
The class compiles but generates a runtime error
Answer : 4
Which
of the following is correct:
1)
String temp [] = new String {"j" "a" "z"};
2)
String temp [] = { "j " " b" "c"};
3)
String temp = {"a", "b", "c"};
4)
String temp [] = {"a", "b", "c"};
Answer
4
What
is the correct declaration of an abstract method that is intended to be public:
1)
public abstract void add();
2)
public abstract void add() {}
3)
public abstract add();
4)
public virtual add();
Answer : 1
Under
what situations do you obtain a default constructor?
1)
When you define any class
2)
When the class has no other constructors
3)
When you define at least one constructor
Answer : 2
Which
of the following can be used to define a constructor for this class, given the
following code:
public class Test {
...
}
1)
public void Test() {...}
2)
public Test() {...}
3)
public static Test() {...}
4)
public static void Test() {...}
Answer : 2
Which
of the following are acceptable to the Java compiler:
(multiple)
1)
if (2 == 3) System.out.println("Hi");
2)
if (2 = 3) System.out.println("Hi");
3)
if (true) System.out.println("Hi");
4)
if (2 != 3) System.out.println("Hi");
5)
if (aString.equals("hello")) System.out.println("Hi");
Answer : 1,3,4,5
Assuming
a method contains code which may raise an Exception (but not a
RuntimeException), what is the correct way for a method to indicate that it
expects the caller to handle that exception:
1)
throw Exception
2)
throws Exception
3)
new Exception
4)
Don't need to specify anything
Answer : 2
What
is the result of executing the following code, using the parameters 4 and 0:
public void divide(int a, int b) {
try {
int c = a / b;
} catch (Exception e) {
System.out.print("Exception ");
} finally {
System.out.println("Finally");
}
1)
Prints out: Exception Finally
2)
Prints out: Finally
3)
Prints out: Exception
4)
No output
Answer : 1
Which
of the following is a legal return type of a method overloading the following
method:
public void add(int a) {...}
1)
void
2)
int
3)
Can be anything
Answer : 3
Which
of the following statements is correct for a method which is overriding the
following method:
public void add(int a) {...}
1)
the overriding method must return void
2)
the overriding method must return int
3)
the overriding method can return whatever it likes
Answer : 1
Given
the following classes defined in separate files, what will be the effect of
compiling and running this class Test?
class Vehicle {
public void drive() {
System.out.println("Vehicle: drive");
}
}
class Car extends Vehicle {
public void drive() {
System.out.println("Car: drive");
}
}
public class Test {
public static void main (String args []) {
Vehicle v;
Car c;
v = new Vehicle();
c = new Car();
v.drive();
c.drive();
v = c;
v.drive();
}
}
1)
Generates a Compiler error on the statement v= c;
2)
Generates runtime error on the statement v= c;
3)
Prints out:
Vehicle:
drive
Car:
drive
Car:
drive
4)
Prints out:
Vehicle:
drive
Car:
drive
Vehicle:
drive
Answer : 3
Where
in a constructor, can you place a call to a constructor defined in the super
class?
1)
Anywhere
2)
The first statement in the constructor
3)
The last statement in the constructor
4)
You can't call super in a constructor
Answer : 2
Which
variables can an inner class access from the class which encapsulates it?
(multiple)
1)
All static variables
2)
All final variables
3)
All instance variables
4)
Only final instance variables
5)
Only final static variables
Answer : 1,2,3
What
class must an inner class extend:
1)
The top level class
2)
The Object class
3)
Any class or interface
4)
It must extend an interface
Answer
3
In
the following code, which is the earliest statement, where the object
originally held in e, may be garbage collected:
1. public class Test {
2. public static void main (String args []) {
3. Employee e = new Employee("Bob", 48);
4. e.calculatePay();
5. System.out.println(e.printDetails());
6. e = null;
7. e = new Employee("Denise", 36);
8. e.calculatePay();
9. System.out.println(e.printDetails());
10. }
11. }
1)
Line 10
2)
Line 11
3)
Line 7
4)
Line 8
5)
Never
Answer : 3
What
is the name of the interface that can be used to define a class that can
execute within its own thread?
1)
Runnable
2)
Run
3)
Threadable
4)
Thread
5)
Executable
Answer : 1
What
is the name of the method used to schedule a thread for execution?
1)
init();
2)
start();
3)
run();
4)
resume();
5)
sleep();
Answer : 2
Which
methods may cause a thread to stop executing?
(multiple)
1)
sleep();
2)
stop();
3)
yield();
4)
wait();
5)
notify();
6)
notifyAll()
7)
synchronized()
Answer : 1,2,3,4
Which
of the following would create a text field able to display 10 characters
(assuming a fixed size font) displaying the initial string "hello":
1)
new TextField("hello", 10);
2)
new TextField("hello");
3)
new textField(10);
4)
new TextField();
Answer : 1
Which
of the following methods are defined on the Graphics class:
(multiple)
1)
drawLine(int, int, int, int)
2)
drawImage(Image, int, int, ImageObserver)
3)
drawString(String, int, int)
4)
add(Component);
5)
setVisible(boolean);
6)
setLayout(Object);
Answer : 1,2,3
Which
of the following layout managers honours the preferred size of a component:
(multiple)
1)
CardLayout
2)
FlowLayout
3)
BorderLayout
4)
GridLayout
Answer : 2
Given
the following code what is the effect of a being 5:
public class Test {
public void add(int a) {
loop: for (int i = 1; i < 3; i++){
for (int j = 1; j < 3; j++) {
if (a == 5) {
break loop;
}
System.out.println(i * j);
}
}
}
}
1)
Generate a runtime error
2)
Throw an ArrayIndexOutOfBoundsException
3)
Print the values: 1, 2, 2, 4
4)
Produces no output
Answer : 4
What
is the effect of issuing a wait() method on an object
1)
If a notify() method has already been sent to that object then it has no effect
2)
The object issuing the call to wait() will halt until another object sends a
notify() or notifyAll() method
3)
An exception will be raised
4)
The object issuing the call to wait() will be automatically synchronized with
any other objects using the receiving object.
Answer : 2
The
layout of a container can be altered using which of the following methods:
(multiple)
1)
setLayout(aLayoutManager);
2)
addLayout(aLayoutManager);
3)
layout(aLayoutManager);
4)
setLayoutManager(aLayoutManager);
Answer : 1
Using
a FlowLayout manager, which is the correct way to add elements to a container:
1)
add(component);
2)
add("Center", component);
3)
add(x, y, component);
4)
set(component);
Answer : 1
Given
that a Button can generate an ActionEvent which listener would you expect to
have to implement, in a class which would handle this event?
1)
FocusListener
2)
ComponentListener
3)
WindowListener
4)
ActionListener
5)
ItemListener
Answer : 4
Which
of the following, are valid return types, for listener methods:
1)
boolean
2)
the type of event handled
3)
void
4)
Component
Answer : 3
Assuming
we have a class which implements the ActionListener interface, which method
should be used to register this with a Button?
1)
addListener(*);
2)
addActionListener(*);
3) addButtonListener(*);
4)
setListener(*);
Answer : 2
In
order to cause the paint(Graphics) method to execute, which of the following is
the most appropriate method to call:
1)
paint()
2)
repaint()
3)
paint(Graphics)
4)
update(Graphics)
5)
None - you should never cause paint(Graphics) to execute
Answer : 2
Which
of the following illustrates the correct way to pass a parameter into an
applet:
1)
<applet code=Test.class age=33 width=100 height=100>
2)
<param name=age value=33>
3)
<applet code=Test.class name=age value=33 width=100 height=100>
4)
<applet Test 33>
Answer : 2
Which
of the following correctly illustrate how an InputStreamReader can be created:
(multiple)
1)
new InputStreamReader(new FileInputStream("data"));
2)
new InputStreamReader(new FileReader("data"));
3)
new InputStreamReader(new BufferedReader("data"));
4)
new InputStreamReader("data");
5)
new InputStreamReader(System.in);
Answer : 1,5
What
is the permanent effect on the file system of writing data to a new
FileWriter("report"), given the file report already exists?
1)
The data is appended to the file
2)
The file is replaced with a new file
3)
An exception is raised as the file already exists
4)
The data is written to random locations within the file
Answer : 2
What
is the effect of adding the sixth element to a vector created in the following
manner:
new Vector(5, 10);
1)
An IndexOutOfBounds exception is raised.
2)
The vector grows in size to a capacity of 10 elements
3)
The vector grows in size to a capacity of 15 elements
4)
Nothing, the vector will have grown when the fifth element was added
Answer : 3
What
is the result of executing the following code when the value of x is 2:
switch (x) {
case 1:
System.out.println(1);
case 2:
case 3:
System.out.println(3);
case 4:
System.out.println(4);
}
1)
Nothing is printed out
2)
The value 3 is printed out
3)
The values 3 and 4 are printed out
4)
The values 1, 3 and 4 are printed out
Answer : 3
What
is the result of compiling and running the Second class?
Consider
the following example:
class First {
public First (String s) {
System.out.println(s);
}
}
public class Second extends First {
public static void main(String args []) {
new Second();
}
}
1)
Nothing happens
2)
A string is printed to the standard out
3)
An instance of the class First is generated
4)
An instance of the class Second is created
5)
An exception is raised at runtime stating that there is no null parameter
constructor in class First.
6)
The class second will not compile as there is no null parameter constructor in
the class First
Answer : 6
What
is the result of executing the following fragment of code:
boolean
flag = false;
if (flag = true) {
System.out.println("true");
} else {
System.out.println("false");
}
1)
true is printed to standard out
2)
false is printed to standard out
3)
An exception is raised
4)
Nothing happens
Answer : 1
Consider
the following classes. What is the result of compiling and running this class?
public class Test {
public static void test() {
this.print();
}
public static void print() {
System.out.println("Test");
}
public static void main(String args []) {
test();
}
}
(multiple)
1)
The string Test is printed to the standard out.
2)
A runtime exception is raised stating that an object has not been created.
3)
Nothing is printed to the standard output.
4)
An exception is raised stating that the method test cannot be found.
5)
An exception is raised stating that the variable this can only be used within
an instance.
6)
The class fails to compile stating that the variable this is undefined.
Answer : 6
Examine
the following class definition:
public class Test {
public static void test() {
print();
}
public static void print() {
System.out.println("Test");
}
public void print() {
System.out.println("Another Test");
}
}
What
is the result of compiling this class:
1)
A successful compilation.
2)
A warning stating that the class has no main method.
3)
An error stating that there is a duplicated method.
4)
An error stating that the method test() will call one or other of the print()
methods.
Answer : 3
What
is the result of compiling and executing the following Java class:
public class ThreadTest extends Thread {
public void run() {
System.out.println("In run");
suspend();
resume();
System.out.println("Leaving run");
}
public static void main(String args []) {
(new ThreadTest()).start();
}
}
1)
Compilation will fail in the method main.
2)
Compilation will fail in the method run.
3)
A warning will be generated for method run.
4)
The string "In run" will be printed to standard out.
5)
Both strings will be printed to standard out.
6)
Nothing will happen.
Answer : 4
Given
the following sequence of Java statements, Which of the following options are
true:
1. StringBuffer sb = new StringBuffer("abc");
2. String s = new String("abc");
3. sb.append("def");
4. s.append("def");
5. sb.insert(1, "zzz");
6. s.concat(sb);
7. s.trim();
(multiple)
1)
The compiler would generate an error for line 1.
2)
The compiler would generate an error for line 2.
3)
The compiler would generate an error for line 3.
4)
The compiler would generate an error for line 4.
5)
The compiler would generate an error for line 5.
6)
The compiler would generate an error for line 6.
7)
The compiler would generate an error for line 7.
Answer : 4,6
What
is the result of executing the following Java class:
import java.awt.*;
public class FrameTest extends Frame {
public FrameTest() {
add (new Button("First"));
add (new Button("Second"));
add (new Button("Third"));
pack();
setVisible(true);
}
public static void main(String args []) {
new FrameTest();
}
}
1)
Nothing happens.
2)
Three buttons are displayed across a window.
3)
A runtime exception is generated (no layout manager specified).
4)
Only the "first" button is displayed.
5)
Only the "second" button is displayed.
6)
Only the "third" button is displayed.
Answer : 6
Consider
the following tags and attributes of tags, which can be used with the
<AAPLET> and </APPLET> tags?
1. CODEBASE
2. ALT
3. NAME
4. CLASS
5. JAVAC
6. HORIZONTALSPACE
7. VERTICALSPACE
8. WIDTH
9. PARAM
10. JAR
(multiple)
1)
line 1, 2, 3
2)
line 2, 5, 6, 7
3)
line 3, 4, 5
4)
line 8, 9, 10
5)
line 8, 9
Answer : 1,5
Which
of the following is a legal way to construct a RandomAccessFile:
1)
RandomAccessFile("data", "r");
2)
RandomAccessFile("r", "data");
3)
RandomAccessFile("data", "read");
4)
RandomAccessFile("read", "data");
Answer : 1
Carefully
examine the following code, When will the string "Hi there" be
printed?
public class StaticTest {
static {
System.out.println("Hi there");
}
public void print() {
System.out.println("Hello");
}
public static void main(String args []) {
StaticTest st1 = new StaticTest();
st1.print();
StaticTest st2 = new StaticTest();
st2.print();
}
}
1)
Never.
2)
Each time a new instance is created.
3)
Once when the class is first loaded into the Java virtual machine.
4)
Only when the static method is called explicitly.
Answer : 3
What
is the result of the following program:
public class Test {
public static void main (String args []) {
boolean a = false;
if (a = true)
System.out.println("Hello");
else
System.out.println("Goodbye");
}
}
1)
Program produces no output but terminates correctly.
2)
Program does not terminate.
3)
Prints out "Hello"
4)
Prints out "Goodbye"
Answer : 3
Examine
the following code, it includes an inner class, what is the result:
public final class Test4 {
class Inner {
void test() {
if (Test4.this.flag); {
sample();
}
}
}
private boolean flag = true;
public void sample() {
System.out.println("Sample");
}
public Test4() {
(new Inner()).test();
}
public static void main(String args []) {
new Test4();
}
}
1)
Prints out "Sample"
2)
Program produces no output but terminates correctly.
3)
Program does not terminate.
4)
The program will not compile
Answer : 1
Carefully
examine the following class:
public class Test5 {
public static void main (String args []) {
/* This is the start of a comment
if (true) {
Test5 = new test5();
System.out.println("Done the test");
}
/* This is another comment */
System.out.println ("The end");
}
}
1)
Prints out "Done the test" and nothing else.
2)
Program produces no output but terminates correctly.
3)
Program does not terminate.
4)
The program will not compile.
5)
The program generates a runtime exception.
6)
The program prints out "The end" and nothing else.
7)
The program prints out "Done the test" and "The end"
Answer : 6
What
is the result of compiling and running the following applet:
import java.applet.Applet;
import java.awt.*;
public class Sample extends Applet {
private String text = "Hello World";
public void init() {
add(new Label(text));
}
public Sample (String string) {
text = string;
}
}
It
is accessed form the following HTML page:
<html>
<title>Sample Applet</title>
<body>
<applet code="Sample.class" width=200
height=200></applet>
</body>
</html>
1)
Prints "Hello World".
2)
Generates a runtime error.
3)
Does nothing.
4)
Generates a compile time error.
Answer : 2
What
is the effect of compiling and (if possible) running this class:
public class Calc {
public static void main (String args []) {
int total = 0;
for (int i = 0, j = 10; total > 30; ++i, --j) {
System.out.println(" i = " + i + " : j = " +
j);
total += (i + j);
}
System.out.println("Total " + total);
}
}
1)
Produce a runtime error
2)
Produce a compile time error
3)
Print out "Total 0"
4)
Generate the following as output:
i =
0 : j = 10
i =
1 : j = 9
i =
2 : j = 8
Total
30
Answer : 3
Utility Package
1)
What is the Vector class?
ANSWER : The Vector class provides the capability to implement a growable array
of objects.
2)
What is the Set interface?
ANSWER : The Set interface provides methods for accessing the elements of a
finite mathematical set.Sets do not allow duplicate elements.
3)
What is Dictionary class?
ANSWER : The Dictionary class is the abstarct super class of Hashtable and
Properties class.Dictionary provides the abstarct functions used to store and
retrieve objects by key-value.This class allows any object to be used as a key
or value.
4)
What is the Hashtable class?
ANSWER : The Hashtable class implements a hash table data structure. A hash
table indexes and stores objects in a dictionary using hash codes as the
objects' keys. Hash codes are integer values that identify objects.
5)
What is the Properties class?
Answer : The properties class is a subclass of Hashtable that can be read from
or written to a stream.It also provides the capability to specify a set of
default values to be used if a specified key is not found in the table. We have
two methods load() and save().
6)
What changes are needed to make the following prg to compile?
import
java.util.*;
class
Ques{
public
static void main (String args[]) {
String
s1 = "abc";
String
s2 = "def";
Vector
v = new Vector();
v.add(s1);
v.add(s2);
String
s3 = v.elementAt(0) + v.elementAt(1);
System.out.println(s3);
}
}
ANSWER : Declare Ques as public B) Cast v.elementAt(0) to a String
C)
Cast v.elementAt(1) to an Object. D) Import java.lang
ANSWER : B) Cast v.elementAt(0) to a String
8)
What is the output of the prg.
import
java.util.*;
class
Ques{
public
static void main (String args[]) {
String
s1 = "abc";
String
s2 = "def";
Stack
stack = new Stack();
stack.push(s1);
stack.push(s2);
try{
String
s3 = (String) stack.pop() + (String) stack.pop() ;
System.out.println(s3);
}catch
(EmptyStackException ex){}
}
}
ANSWER : abcdef B) defabc C) abcabc D) defdef
ANSWER : B) defabc
9)
Which of the following may have duplicate elements?
ANSWER : Collection B) List C) Map D) Set
ANSWER : A and B Neither a Map nor a Set may have duplicate elements.
10)
Can null value be added to a List?
ANSWER : Yes.A Null value may be added to any List.
11)
What is the output of the following prg.
import
java.util.*;
class
Ques{
public
static void main (String args[]) {
HashSet
set = new HashSet();
String
s1 = "abc";
String
s2 = "def";
String
s3 = "";
set.add(s1);
set.add(s2);
set.add(s1);
set.add(s2);
Iterator
i = set.iterator();
while(i.hasNext())
{
s3
+= (String) i.next();
}
System.out.println(s3);
}
}
A)
abcdefabcdef B) defabcdefabc C) fedcbafedcba D) defabc
ANSWER : D) defabc. Sets may not have duplicate elements.
12)
Which of the following java.util classes support internationalization?
A)
Locale B) ResourceBundle C) Country D) Language
ANSWER : A and B . Country and Language are not java.util classes.
13)
What is the ResourceBundle?
The
ResourceBundle class also supports internationalization.
ResourceBundle
subclasses are used to store locale-specific resources that can be loaded by a
program to tailor the program's appearence to the paticular locale in which it
is being run. Resource Bundles provide the capability to isolate a program's
locale-specific resources in a standard and modular manner.
14)
How are Observer Interface and Observable class, in java.util package, used?
ANSWER : Objects that subclass the Observable class maintain a list of
Observers. When an Observable object is updated it invokes the update() method of
each of its observers to notify the observers that it has changed state. The
Observer interface is implemented by objects that observe Observable objects.
15)
Which java.util classes and interfaces support event handling?
ANSWER : The EventObject class and the EventListener interface support event
processing.
16)
Does java provide standard iterator functions for inspecting a collection of
objects?
ANSWER : The Enumeration interface in the java.util package provides a
framework for stepping once through a collection of objects. We have two
methods in that interface.
public
interface Enumeration {
boolean
hasMoreElements();
Object
nextElement();
}
17)
The Math.random method is too limited for my needs- How can I generate random
numbers more flexibly?
ANSWER : The random method in Math class provide quick, convienient access to
random numbers, but more power and flexibility use the Random class in the
java.util package.
double
doubleval = Math.random();
The
Random class provide methods returning float, int, double, and long values.
nextFloat()
// type float; 0.0 <= value < 1.0
nextDouble()
// type double; 0.0 <= value < 1.0
nextInt()
// type int; Integer.MIN_VALUE <= value <= Integer.MAX_VALUE
nextLong()
// type long; Long.MIN_VALUE <= value <= Long.MAX_VALUE
nextGaussian()
// type double; has Gaussian("normal") distribution with mean 0.0 and
standard deviation 1.0)
Eg.
Random r = new Random();
float
floatval = r.nextFloat();
18)
How can we get all public methods of an object dynamically?
ANSWER : By using getMethods(). It return an array of method objects
corresponding to the public methods of this class.
getFields()
returns an array of Filed objects corresponding to the public Fields(variables)
of this class.
getConstructors()
returns an array of constructor objects corresponding to the public
constructors of this class.
JDBC
1)
What are the steps involved in establishing a connection?
ANSWER : This involves two steps: (1) loading the driver and (2) making the
connection.
2)
How can you load the drivers?
ANSWER : Loading the driver or drivers you want to use is very simple and
involves just one line of code. If, for example, you want to use the JDBC-ODBC
Bridge driver, the following code will load it:
Eg.
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Your
driver documentation will give you the class name to use. For instance, if the
class name is jdbc.DriverXYZ , you would load the driver with the following
line of code:
Eg.
Class.forName("jdbc.DriverXYZ");
3)
What Class.forName will do while loading drivers?
ANSWER : It is used to create an instance of a driver and register it with the
DriverManager.
When
you have loaded a driver, it is available for making a connection with a DBMS.
4)
How can you make the connection?
ANSWER : In establishing a connection is to have the appropriate driver connect
to the DBMS. The following line of code illustrates the general idea:
Eg.
String
url = "jdbc:odbc:Fred";
Connection
con = DriverManager.getConnection(url, "Fernanda", "J8");
5)
How can you create JDBC statements?
ANSWER : A Statement object is what sends your SQL statement to the DBMS. You
simply create a Statement object and then execute it, supplying the appropriate
execute method with the SQL statement you want to send. For a SELECT statement,
the method to use is executeQuery. For statements that create or modify tables,
the method to use is executeUpdate.
Eg.
It
takes an instance of an active connection to create a Statement object. In the
following example, we use our Connection object con to create the Statement
object stmt :
Statement
stmt = con.createStatement();
6)
How can you retrieve data from the ResultSet?
ANSWER : Step 1.
JDBC
returns results in a ResultSet object, so we need to declare an instance of the
class ResultSet to hold our results. The following code demonstrates declaring
the ResultSet object rs.
Eg.
ResultSet
rs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM COFFEES");
Step2.
String
s = rs.getString("COF_NAME");
The
method getString is invoked on the ResultSet object rs , so getString will
retrieve (get) the value stored in the column COF_NAME in the current row of rs
7)
What are the different types of Statements?
ANSWER : 1.Statement (use createStatement method) 2. Prepared Statement (Use
prepareStatement method) and 3. Callable Statement (Use prepareCall)
8)
How can you use PreparedStatement?
ANSWER : This special type of statement is derived from the more general class,
Statement.If you want to execute a Statement object many times, it will
normally reduce execution time to use a PreparedStatement object instead.
The
advantage to this is that in most cases, this SQL statement will be sent to the
DBMS right away, where it will be compiled. As a result, the PreparedStatement
object contains not just an SQL statement, but an SQL statement that has been
precompiled. This means that when the PreparedStatement is executed, the DBMS
can just run the PreparedStatement 's SQL statement without having to compile
it first.
Eg.
PreparedStatement
updateSales = con.prepareStatement("UPDATE COFFEES SET SALES = ? WHERE
COF_NAME LIKE ?");
9)
What setAutoCommit does?
ANSWER : When a connection is created, it is in auto-commit mode. This means
that each individual SQL statement is treated as a transaction and will be
automatically committed right after it is executed. The way to allow two or
more statements to be grouped into a transaction is to disable auto-commit mode
Eg.
con.setAutoCommit(false);
Once
auto-commit mode is disabled, no SQL statements will be committed until you
call the method commit explicitly.
Eg.
con.setAutoCommit(false);
PreparedStatement
updateSales = con.prepareStatement(
"UPDATE
COFFEES SET SALES = ? WHERE COF_NAME LIKE ?");
updateSales.setInt(1,
50);
updateSales.setString(2,
"Colombian");
updateSales.executeUpdate();
PreparedStatement
updateTotal = con.prepareStatement("UPDATE COFFEES SET TOTAL = TOTAL + ?
WHERE COF_NAME LIKE ?");
updateTotal.setInt(1,
50);
updateTotal.setString(2,
"Colombian");
updateTotal.executeUpdate();
con.commit();
con.setAutoCommit(true);
10)
How to call a Strored Procedure from JDBC?
ANSWER : The first step is to create a CallableStatement object. As with
Statement an and PreparedStatement objects, this is done with an open
Connection
object.
A CallableStatement object contains a call to a stored procedure;
Eg.
CallableStatement
cs = con.prepareCall("{call SHOW_SUPPLIERS}");
ResultSet
rs = cs.executeQuery();
11)
How to Retrieve Warnings?
ANSWER : SQLWarning objects are a subclass of SQLException that deal with
database access warnings. Warnings do not stop the execution of an application,
as exceptions do; they simply alert the user that something did not happen as
planned.
A
warning can be reported on a Connection object, a Statement object (including
PreparedStatement and CallableStatement objects), or a ResultSet object. Each
of these classes has a getWarnings method, which you must invoke in order to
see the first warning reported on the calling object
Eg.
SQLWarning
warning = stmt.getWarnings();
if
(warning != null) {
System.out.println("\n---Warning---\n");
while
(warning != null) {
System.out.println("Message:
" + warning.getMessage());
System.out.println("SQLState:
" + warning.getSQLState());
System.out.print("Vendor
error code: ");
System.out.println(warning.getErrorCode());
System.out.println("");
warning
= warning.getNextWarning();
}
}
12)
How can you Move the Cursor in Scrollable Result Sets ?
ANSWER : One of the new features in the JDBC 2.0 API is the ability to move a
result set's cursor backward as well as forward. There are also methods that let
you move the cursor to a particular row and check the position of the cursor.
Eg.
Statement
stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_READ_ONLY);
ResultSet
srs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM COFFEES");
The
first argument is one of three constants added to the ResultSet API to indicate
the type of a ResultSet object: TYPE_FORWARD_ONLY, TYPE_SCROLL_INSENSITIVE ,
and TYPE_SCROLL_SENSITIVE .
The
second argument is one of two ResultSet constants for specifying whether a
result set is read-only or updatable: CONCUR_READ_ONLY and CONCUR_UPDATABLE .
The point to remember here is that if you specify a type, you must also specify
whether it is read-only or updatable. Also, you must specify the type first, and
because both parameters are of type int , the compiler will not complain if you
switch the order.
Specifying
the constant TYPE_FORWARD_ONLY creates a nonscrollable result set, that is, one
in which the cursor moves only forward. If you do not specify any constants for
the type and updatability of a ResultSet object, you will automatically get one
that is TYPE_FORWARD_ONLY and CONCUR_READ_ONLY
13)
What’s the difference between TYPE_SCROLL_INSENSITIVE , and
TYPE_SCROLL_SENSITIVE?
ANSWER : You will get a scrollable ResultSet object if you specify one of these
ResultSet constants.The difference between the two has to do with whether a
result set reflects changes that are made to it while it is open and whether
certain methods can be called to detect these changes. Generally speaking, a
result set that is TYPE_SCROLL_INSENSITIVE does not reflect changes made while
it is still open and one that is TYPE_SCROLL_SENSITIVE does. All three types of
result sets will make changes visible if they are closed and then reopened
Eg.
Statement
stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
ResultSet
srs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM COFFEES");
srs.afterLast();
while
(srs.previous()) {
String
name = srs.getString("COF_NAME");
float
price = srs.getFloat("PRICE");
System.out.println(name
+ " " + price);
}
14)
How to Make Updates to Updatable Result Sets?
ANSWER : Another new feature in the JDBC 2.0 API is the ability to update rows
in a result set using methods in the Java programming language rather than
having to send an SQL command. But before you can take advantage of this
capability, you need to create a ResultSet object that is updatable. In order
to do this, you supply the ResultSet constant CONCUR_UPDATABLE to the
createStatement method.
Eg.
Connection
con = DriverManager.getConnection("jdbc:mySubprotocol:mySubName");
Statement
stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet
uprs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM COFFEES");
Networking Concepts
1)
The API doesn't list any constructors for InetAddress- How do I create an
InetAddress instance?
ANSWER : In case of InetAddress the three methods getLocalHost, getByName,
getByAllName can be used to create instances.
E.g.
InetAddress
add1;
InetAddress
add2;
try{
add1
= InetAddress.getByName("java.sun.com");
add2
= InetAddress.getByName("199.22.22.22");
}catch(UnknownHostException
e){}
2)
Is it possible to get the Local host IP?
ANSWER : Yes. Use InetAddress's getLocalHost method.
3)
What's the Factory Method?
ANSWER : Factory methods are merely a convention whereby static methods in a
class return an instance of that class. The InetAddress class has no visible
constructors. To create an InetAddress object, you have to use one of the
available factory methods. In InetAddress the three methods getLocalHost,
getByName, getByAllName can be used to create instances of InetAddress.
4)
What’s the difference between TCP and UDP?
ANSWER : These two protocols differ in the way they carry out the action of
communicating. A TCP protocol establishes a two way connection between a pair
of computers, while the UDP protocol is a one-way message sender. The common
analogy is that TCP is like making a phone call and carrying on a two-way
communication, while UDP is like mailing a letter.
5)
What is the Proxy Server?
ANSWER : A proxy server speaks the client side of a protocol to another server.
This is often required when clients have certain restrictions on which servers
they can connect to. And when several users are hitting a popular web site, a
proxy server can get the contents of the web server's popular pages once,
saving expensive internetwork transfers while providing faster access to those
pages to the clients.
Also,
we can get multiple connections for a single server.
6)
What are the seven layers of OSI model?
ANSWER : Application, Presentation, Session, Transport, Network, DataLink,
Physical Layer.
What
Transport Layer does?
ANSWER : It ensures that the mail gets to its destination. If a packet fails to
get its destination, it handles the process of notifying the sender and
requesting that another packet be sent.
8)
What is DHCP?
ANSWER : Dynamic Host Configuration Protocol, a piece of the TCP/IP protocol
suite that handles the automatic assignment of IP addresses to clients.
9)
What is SMTP?
ANSWER : Simple Mail Transmission Protocol, the TCP/IP Standard for Internet
mails. SMTP exchanges mail between servers; contrast this with POP, which
transmits mail between a server and a client.
10)
In OSI N/w architecture, the dialogue control and token management are
responsibilities of...
Answer : Network b) Session c) Application d) DataLink
ANSWER : b) Session Layer.
11)
In OSI N/W Architecture, the routing is performed by ______
Answer : Network b) Session c) Application d) DataLink
ANSWER : Answer : Network Layer.
Networking
What
is the difference between URL instance and URLConnection instance?
ANSWER : A URL instance represents the location of a resource, and a URLConnection
instance represents a link for accessing or communicating with the resource at
the location.
2)
How do I make a connection to URL?
ANSWER : You obtain a URL instance and then invoke openConnection on it.
URLConnection
is an abstract class, which means you can't directly create instances of it
using a constructor. We have to invoke openConnection method on a URL instance,
to get the right kind of connection for your URL.
Eg. URL url;
URLConnection
connection;
try{
url = new URL("...");
conection
= url.openConnection();
}catch
(MalFormedURLException e) { }
A
socket is one end-point of a two-way communication link between two programs
running on the network. A socket is bound to a port number so that the TCP
layer can identify the application that data is destined to be sent.Socket
classes are used to represent the connection between a client program and a
server program. The java.net package provides two classes--Socket and
ServerSocket--which implement the client side of the connection and the server
side of the connection, respectively.
What
information is needed to create a TCP Socket?
ANSWER : The Local System’s IP Address and Port Number.
And
the Remote System's IPAddress and Port Number.
5)
What are the two important TCP Socket classes?
ANSWER : Socket and ServerSocket.
ServerSocket
is used for normal two-way socket communication. Socket class allows us to read
and write through the sockets.
getInputStream()
and getOutputStream() are the two methods available in Socket class.
When
MalformedURLException and UnknownHostException throws?
ANSWER : When the specified URL is not connected then the URL throw
MalformedURLException and If InetAddress’ methods getByName and getLocalHost
are unabletoresolve the host name they throwan UnknownHostException.
Servlets
1)
What is the servlet?
ANSWER : Servlets are modules that extend request/response-oriented servers,
such as Java-enabled web servers. For example, a servlet might be responsible
for taking data in an HTML order-entry form and applying the business logic
used to update a company's order database.
Servlets
are to servers what applets are to browsers. Unlike applets, however, servlets
have no graphical user interface.
2)
Whats the advantages using servlets than using CGI?
ANSWER : Servlets provide a way to generate dynamic documents that is both
easier to write and faster to run. Servlets also address the problem of doing
server-side programming with platform-specific APIs: they are developed with
the Java Servlet API, a standard Java extension.
3)
What are the uses of Servlets?
ANSWER : A servlet can handle multiple requests concurrently, and can
synchronize requests. This allows servlets to support systems such as on-line
conferencing.
Servlets
can forward requests to other servers and servlets.Thus servlets can be used to
balance load among several servers that mirror the same content, and to
partition a single logical service over several servers, according to task type
or organizational boundaries.
4)
Which pakage provides interfaces and classes for writing servlets?
ANSWER : javax
5)
Whats the Servlet Interfcae?
ANSWER : The central abstraction in the Servlet API is the Servlet interface.
All servlets implement this interface, either directly or, more commonly, by
extending a class that implements it such as HttpServlet.
Servlets-->Generic
Servlet-->HttpServlet-->MyServlet.
The
Servlet interface declares, but does not implement, methods that manage the
servlet and its communications with clients. Servlet writers provide some or
all of these methods when developing a servlet.
6)
When a servlet accepts a call from a client, it receives two objects- What are
they?
ANSWER : ServeltRequest: Which encapsulates the communication from the client
to the server.
ServletResponse:
Whcih encapsulates the communication from the servlet back to the client.
ServletRequest
and ServletResponse are interfaces defined by the javax.servlet package.
7)
What information that the ServletRequest interface allows the servlet access
to?
ANSWER : Information such as the names of the parameters passed in by the
client, the protocol (scheme) being used by the client, and the names of the
remote host that made the request and the server that received it.
The
input stream, ServletInputStream.Servlets use the input stream to get data from
clients that use application protocols such as the HTTP POST and PUT methods.
8)
What information that the ServletResponse interface gives the servlet methods for
replying to the client?
ANSWER : It Allows the servlet to set the content length and MIME type of the
reply.
Provides
an output stream, ServletOutputStream and a Writer through which the servlet
can send the reply data.
9)
What is the servlet Lifecycle?
ANSWER : Each servlet has the same life cycle:
A
server loads and initializes the servlet (init())
The
servlet handles zero or more client requests (service())
The
server removes the servlet (destroy())
(some
servers do this step only when they shut down)
10)
How HTTP Servlet handles client requests?
ANSWER : An HTTP Servlet handles client requests through its service method.
The service method supports standard HTTP client requests by dispatching each
request to a method designed to handle that request. 1
Encapsulation :
Encapsulation
is the mechanism that binds together code and the data it manipulates and keeps
both safe from outside interference and misuse.
Inheritance:
Inheritance
is the process by which one object acquires the properties of another object.
Polymorphism:
Polymorphism
is a feature that allows one interface to be used for a general class of
actions. The specific action is determined by the exact nature of actions.
Code Blocks:
Two
or more statements which is allowed to be grouped into blocks of code is
otherwise called as Code Blocks.This is done by enclosing the statements
between opening and closing curly braces.
Floating-point numbers:
Floating-point
numbers which is also known as real numbers, are used when evaluating expressions
that require fractional precision.
Unicode:
Unicode
defines a fully international character set that can represent all of the
characters found in all human languages. It is a unification of dozens of
character sets, such as Latin, Greek, Arabic and many more.
Booleans:
Java
has a simple type called boolean, for logical values. It can have only on of
two possible values, true or false.
Casting:
A
cast is simply an explicit type conversion. To create a conversion between two
incompatible types, you must use a cast.
Arrays:
An
array is a group of like-typed variables that are referred to by a common name.
Arrays offer a convenient means of grouping related information. Arrays of any
type can be created and may have one or more dimension.
Relational Operators:
The
relational operators determine the relationship that one operand has to the
other. They determine the equality and ordering.
11.Short-Circuit Logical Operators:
The
secondary versions of the Boolean AND and OR operators are known as short-
circuit
logical operators. It is represented by || and &&..
12. Switch:
The
switch statement is Java’s multiway branch statement. It provides an easy way
to
dispatch
execution to different parts of your code based on the value of an
experession.
13. Jump Statements:
Jump
statements are the statements which transfer control to another part of your
program.
Java Supports three jump statements: break, continue, and return.
14. Instance Variables:
The
data, or variable, defined within a class are called instance variable.
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