programming to an interface

[Rahul Kakkar]

say i have the following:

  
public interface anInterface
{
void aMethod();
void anotherMethod();
}
 
public class A implements anInterface
{
public void aMethod()
{
//...
}
public void anotherMethod()
{
//...
}
}
 
public class B implements anInterface
{
public void aMethod()
{
//...
}
public void anotherMethod()
{
//...
}

public void methodSpecificToClassB()
{
//...
}
}

the thing is we should always program to an interface. now if i wanted to insert a method specific to class B.. would this be a time to redesign? cause all old code would program to anInterface. wats the best way to tackle such a situation?

[Jim Yingst]

You can create a new interface:

public interface anotherInterface extends anInterface
{
void methodSpecificToClassB();
}

Then let class B implement this interface. Any client code that needs to use methodSpecificToClassB() will have to use this new interface . Any code which does not need methodSpecificToClassB() can continue using the old one.
[ November 27, 2005: Message edited by: Jim Yingst ]

[Tony Morris]

You would create a subinterface with the new operation and have B implement that. Implementing more than 1 interface is nasty.

[Jim Yingst]

Uh... yes. Good idea.

[Rahul Kakkar]

Okay. Basically B could just implement "anotherInterface". Cool. thanks

[Jesper de Jong]

Programming to an interface is often a good idea, but beware that you go too far (making your code unnecessarily long and complex) if you make an interface for every single class you write...

[Rahul Kakkar]

true.