|
| 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.
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|
| 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. |
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|
| 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. |
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|
| 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. |
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|
| 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. |
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|
| Q: |
What is HashMap and
Map? |
| A: |
Map is Interface
and Hashmap is class that implements that. |
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|
| 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.
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| |
|
| Q: |
Difference
between Vector and ArrayList? |
| A: |
Vector is
synchronized whereas arraylist is not. |
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|
| 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. |
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|
| 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). TOP |
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