This week's book giveaway is in the OCMJEA forum.
We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line!
See this thread for details.
The moose likes Beginning Java and the fly likes Abstract class and Interface Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login


Win a copy of OCM Java EE 6 Enterprise Architect Exam Guide this week in the OCMJEA forum!
JavaRanch » Java Forums » Java » Beginning Java
Bookmark "Abstract class and Interface" Watch "Abstract class and Interface" New topic
Author

Abstract class and Interface

Ashok Pradhan
Ranch Hand

Joined: Dec 17, 2007
Posts: 180

What is the difference between an Abstract class and Interface?
Jesper de Jong
Java Cowboy
Saloon Keeper

Joined: Aug 16, 2005
Posts: 14117
    
  16

See: http://faq.javaranch.com/java/InterfaceVsAbstractClass

This is a very frequently asked question. If you want to find more information, please search the forums here or search with Google, and you'll find a lot more information.


Java Beginners FAQ - JavaRanch SCJP FAQ - The Java Tutorial - Java SE 7 API documentation
Scala Notes - My blog about Scala
Campbell Ritchie
Sheriff

Joined: Oct 13, 2005
Posts: 38519
    
  23
I trust you have looked in books and the Java Tutorial?

An abstract class is one which you do not mean to instantiate; it can have abstract methods, implemented methods, fields, constructors, etc.

Imagine interfaces as being very very abstract classes.
An interface (ideally) only has methods. All the methods are empty, so you only write a list of method headings. You usually miss out "public" and "abstract." An interface might look like thisYou can't compile that because it has "java.lang" in. If you add lots of documentation comments you will reconstruct the Comparable interface, at least before Java 5 when it was Comparable rather than Comparable<T>.

When your class (unless it is an abstract class) implements an interface it also has to implement all its methods, so as to maintain the contract in the original documentation.

You can instantiate an abstract class several ways, but the one you are probably familiar is to write extends. You can implement several interfaces, so using interfaces has several advantages:
  • You can implement certain functionality from the interfaces.
  • A class using the objects can check whether a particular method is available by using "instanceof Comparable" or similar. Much quicker than looking for the method.
  • I am sure other people will have more points to add.
     
    I agree. Here's the link: http://aspose.com/file-tools
     
    subject: Abstract class and Interface