JAVA INTERVIEW QUESTIONS
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.
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.
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.
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. then only interface can help.
What are pass by reference and pass by value?
Pass by Reference means the passing the address itself rather than passing
the value. Pass by Value means passing a copy of the value to be passed.
What is HashMap and Map?
Map is Interface and Hashmap is class that implements that.
What is the difference between HashMap and HashTable?
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 doesn’t allow). HashMap does not guarantee that the order of the
map will remain constant over time. HashMap is unsynchronized and Hashtable is
synchronized.
What is the difference between Vector and ArrayList?
Vector is synchronized whereas arraylist is not.
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.
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.
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.
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. then only interface can help.
What are pass by reference and pass by value?
Pass by Reference means the passing the address itself rather than passing
the value. Pass by Value means passing a copy of the value to be passed.
What is HashMap and Map?
Map is Interface and Hashmap is class that implements that.
What is the difference between HashMap and HashTable?
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 doesn’t allow). HashMap does not guarantee that the order of the
map will remain constant over time. HashMap is unsynchronized and Hashtable is
synchronized.
What is the difference between Vector and ArrayList?
Vector is synchronized whereas arraylist is not.
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.
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.
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.
Default: What you get by default i.e., without any access modifier (i.e.,
public private or protected).It means that it is visible to all within a particular
package.
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 (i.e., 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.
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.
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.
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.
Default: What you get by default i.e., without any access modifier (i.e.,
public private or protected).It means that it is visible to all within a particular
package.
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 (i.e., 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.
No comments:
Post a Comment