Gopinath
abstract class and interface
1 Answer(s)      7 years ago
Posted in : Java Beginners
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November 24, 2008 at 10:51 PM


Hi friend,


Abstract classes

In java programming language, abstract classes are those that works only as the parent class or the base class. Subclasses are derived to implement the methods inherited from the abstract class (base class). Abstract classes are not instantiated directly. First extend the base class and then instantiate (create objects). Abstract classes are generic in nature and implement to those methods that are used commonly by the subclasses with common implementation

Abstract Method

An abstract method one that have the empty implementation. All the methods in any interface are abstract by default. Abstract method provides the standardization for the " name and signature" of any method. One can extend and implement to these methods in their own classes according to the

These classes that contain one or more abstract methods.
An abstract method is a method that is declared, but contains no implementation.
It may not be instantiated, and require subclasses to provide implementations for the abstract methods.


Example of abstract class and Method

Modeling the behavior of animals, by creating a class hierachy that started with a base class called Animal.
Animals are capable of doing different things like flying, digging and walking,
but there are some common operations as well like eating and sleeping. Some common operations are performed by all animals,
but in a different way as well. When an operation is performed in a different way,


public abstract Animal
{
public void eat(Food food)
{
// do something with food....
}

public void sleep(int hours)
{
try
{
// 1000 milliseconds * 60 seconds * 60 minutes * hours
Thread.sleep ( 1000 * 60 * 60 * hours);
}
catch (Exception ie) { /* ignore */ }
}

public abstract void makeNoise();
}


Now, any animal that to be instantiated (like a dog or cow) must implement the makeNoise method - otherwise
it is impossible to create an instance of that class. Let's look at a Dog and Cow subclass that extends the Animal class.

public Dog extends Animal
{
public void makeNoise() { System.out.println ("Bark! Bark!"); }
}

public Cow extends Animal
{
public void makeNoise() { System.out.println ("Moo! Moo!"); }
}

Why not declare an abstract class as an interface, and have the Dog and Cow implement the interface.
Sure you could - but you'd also need to implement the eat and sleep methods. By using abstract classes,
you can inherit the implementation of other (non-abstract) methods. You can't do that with interfaces -
an interface cannot provide any method implementations.

For difference between interface and abstract class visit to :

http://www.roseindia.net/help/java/a/interface-vs-abstract-class.shtml

http://www.roseindia.net/java/master-java/abstract-class.shtml

http://www.roseindia.net/java/master-java/interface.shtml

Thanks









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