Use Of Interface

[Biswomohan Pattanaik]

I have a doubt
//Interface A

 
interface A{
public void add();
public void sub();
public void multiplication();
}
 
//Class B that Implements A
class B implements A{
public void add(){
 int a=30;
 int b=40;
 int c=a+b;
 System.out.println("The result of Addition is:-"c);  
}
public void sub(){
 int a=80;
 int b=40;
 int c=a-b;
 System.out.println("The result of Substraction is:-"c);
}
public void multiplication(){
 int a=80;
 int b=40;
 int c=a*b;
 System.out.println("The result of Multiplication is:-"c);
}
public void division(){
 int a=80;
 int b=40;
 int c=a/b;
 System.out.println("The result of Division is:-"c); 
}
}
//Anaother class C that use B's method
class C{
public static void main(String[]args){
    //what is the differnce
   //I have a doubt why we use this line
 
   A a=new B();
   a.add();
   B b=new B();
   b.add();
 }
}

I have a doubt,In class C I am accessing the B's add()through 2 referance variables one is class type and another is interface type.ok
My doubt is what's the differance?
which is adviceable to use?


thanks
Biswo
[ November 02, 2008: Message edited by: Maneesh Godbole ]

[pawan chopra]

You will not see any difference in the output because you have assigned same object to both the references.

Regarding which one is good to use is the the first one

that is A a = new B();

if you have 2 implemntation and at run time you have to decide that which one to be used then 1st is more appropriate.

[Venkata Kumar]

  A a=new B();

When interface has reference to a object then only methods declared in the interface can be called.

    
B b=new B();

Here reference to object is via Class name and all the public methods of Class B are accessible.

[vipin raimcs]

A a = new B(); is advisable to use, this is because of business purpose. Also creation of objects is left on some factory classes. So client code is totally unaware of the fact that what they are using. They just only know if A a.