Thursday, June 24, 2010

Nitin Gudle



Java Interview Questions






Hi guys if you are thinking to go for java interview then here you can see all the questions through which you can crack any java interview.....
I hope my information will help you....







pages.....
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Question:

What is the difference between an Interface
and an Abstract class?





Question:

What is the purpose of garbage collection
in Java, and when is it used?
 






Question: 

Describe synchronization in respect to multithreading.



Question: 

Explain different way of using thread?
 






Question: 

What are pass by reference and passby value?






Question: 

What is HashMap and Map?






Question: 

Difference between HashMap and HashTable?






Question:

Difference between Vector and ArrayList?






Question: 

Difference between Swing and Awt?






Question: 

What is the difference between a constructor
and a method?






Question: 

What is an Iterator?






Question: 

State the significance of public, private,
protected, default modifiers both singly
and in combination and state the effect
of package relationships on declared items
qualified by these modifiers.






Question:

What is an abstract class?






Question:

What is static in java?






Question:



What is final?















Q:

What
is the difference between an Interface
and an Abstract class?

A: An abstract class can have instance methods
that implement a default behavior. An Interface
can only declare constants and instance
methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.

.
 



Q:

What
is the purpose of garbage collection in
Java, and when is it used?
A: The
purpose of garbage collection is to identify
and discard objects that are no longer needed
by a program so that their resources can
be reclaimed and reused. A Java object is
subject to garbage collection when it becomes
unreachable to the program in which it is
used.
 



Q:

Describe
synchronization in respect to multithreading.
A: With
respect to multithreading, synchronization
is the capability to control the access
of multiple threads to shared resources.
Without synchonization, it is possible for
one thread to modify a shared variable while
another thread is in the process of using
or updating same shared variable. This usually
leads to significant errors. 
 



Q:


Explain different way of using thread?

A: The
thread could be implemented by using runnable
interface or by inheriting from the Thread
class. The former is more advantageous,
'cause when you are going for multiple inheritance..the
only interface can help.
 



Q:

What
are pass by reference and passby value?

A: Pass By Reference means the
passing the address itself rather than passing
the value. Passby Value means passing a
copy of the value to be passed. 
 



Q:

What
is HashMap and Map?
A: Map
is Interface and Hashmap is class that implements
that.
 



Q:

Difference
between HashMap and HashTable?
A: The
HashMap class is roughly equivalent
to Hashtable, except that it is unsynchronized
and permits nulls. (HashMap allows null
values as key and value whereas Hashtable
doesnt allow). HashMap does not guarantee
that the order of the map will remain constant
over time. HashMap is unsynchronized and
Hashtable is synchronized.
 



Q:


Difference between Vector and ArrayList?
A: Vector
is synchronized whereas arraylist is not.
 



Q:

Difference
between Swing and Awt?
A: AWT
are heavy-weight componenets. Swings are
light-weight components. Hence swing works
faster than AWT.
 



Q:

What
is the difference between a constructor
and a method?

A: A
constructor is a member function of a class
that is used to create objects of that class.
It has the same name as the class itself,
has no return type, and is invoked using
the new operator.

A method is an ordinary member function
of a class. It has its own name, a return
type (which may be void), and is invoked
using the dot operator.
 



Q:

What
is an Iterator?
A: Some
of the collection classes provide traversal
of their contents via a java.util.Iterator
interface. This interface allows you to
walk through a collection of objects, operating
on each object in turn. Remember when using
Iterators that they contain a snapshot of
the collection at the time the Iterator
was obtained; generally it is not advisable
to modify the collection itself while traversing
an Iterator.
 



Q:


State
the significance of public, private, protected,
default modifiers both singly and in combination
and state the effect of package relationships
on declared items qualified by these modifiers.
A: public
: Public class is visible
in other packages, field is visible everywhere
(class must be public too)

private : Private
variables or methods may be used only by
an instance of the same class that declares
the variable or method, A private feature
may only be accessed by the class that owns
the feature.

protected : Is
available to all classes in the same package
and also available to all subclasses of
the class that owns the protected feature.This
access is provided even to subclasses that
reside in a different package from the class
that owns the protected feature.

default :What
you get by default ie, without any access
modifier (ie, public private or protected).It
means that it is visible to all within a
particular package.
 



Q:

What
is an abstract class?
A:
Abstract class must be extended/subclassed
(to be useful). It serves as a template.
A class that is abstract may not be instantiated
(ie, you may not call its constructor),
abstract class may contain static data.
Any class with an abstract method is automatically
abstract itself, and must be declared as
such.

A class may be declared abstract even if
it has no abstract methods. This prevents
it from being instantiated.
 



Q:

What
is static in java?
A: Static
means one per class, not one for each object
no matter how many instance of a class might
exist. This means that you can use them
without creating an instance of a class.Static
methods are implicitly final, because overriding
is done based on the type of the object,
and static methods are attached to a class,
not an object. A static method in a superclass
can be shadowed by another static method
in a subclass, as long as the original method
was not declared final. However, you can't
override a static method with a nonstatic
method. In other words, you can't change
a static method into an instance method
in a subclass.
 








Q:

What
is final?
A: A
final class can't be extended ie., final
class may not be subclassed. A final method
can't be overridden when its class is inherited.
You can't change value of a final variable
(is a constant).
 





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