What is the Composition in Java

[Santoshbk]

Hello to Everybody,

What is the Composition in Java with respect to inheritance. When should i go for Composition than inheritance. What is its Advantage.

Waiting for your reply.

Thanks in Advance.
Santosh

[Eranga]

I don't see much difference there actually. In composition you have to use an instance variable that are reference to other object. But in inheritance you have to extend the supper class into the sub class.

Something like this.

In composition,

Code:

class One{
// Called back-end class
}
class Two{
private One objOne = new One();
// Called front-end class
}

In inheritance,

Code:

class One{
// Called the supper class
}
class Two extend One{
// Called the sub class
}

So what we have to mainly focus on the use of instance than extending a class. Actually it depends on the situation you work on. If you create more instance it can be a mess at all.

[rpwtdj]

If you have to override a final method in class A, you can define a class B that has a instance variable referring an object of class A, and "wrap" the whole class.

Code:

class A{
final void methodA(){
 ...
 }
}

Code:

class B{
class A ref;
final void methodA()
 {
 ...
 ref.methodA();
 ...
 }
}

[Eranga]

True, but what the Composition means use an instance of a class inside the other.

This is a good choice, but I'm not how many people really familiar with this.

[javarishi]

Can Any One Say What Is The Defference Between Composition, Association, Aggregation?