1. What is the difference between a constructor
and a method?
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.
2. What is the purpose of garbage collection in
Java, and when is it used?
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.
3. Describe synchronization in respect to
multithreading.
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.
4. What is an abstract class?
,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.
5. What is the difference between an Interface and
an Abstract class?
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.
6. Explain different way of using thread?
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.
What is an Iterator?
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.
8. 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.
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.
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.
9. What is static in java?
and a method?
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.
2. What is the purpose of garbage collection in
Java, and when is it used?
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.
3. Describe synchronization in respect to
multithreading.
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.
4. What is an abstract class?
,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.
5. What is the difference between an Interface and
an Abstract class?
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.
6. Explain different way of using thread?
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.
What is an Iterator?
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.
8. 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.
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.
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.
9. What is static in java?
