Programming to an interface

[mo sayed]

Hi,
Recommended practice is to ensure that we code objects to an interface,
enabling us to exploit polymorphic behaviour. Does this mean that
all classes I create should implement an interface.
regards,
Mo

[Oliver Kamps]

Hi,

in short: no, it doesn't mean that.

A little longer: First, polymorphic behavior does not depend on a class having an interface; a class hierarchy without any interface can exhibit polymorphic behavior.

Providing an interface allows you to separate the implementation of an abstraction (i.e. the class) from its interface (i.e. the interface itself). You can exchange or modify the implementation without affecting code programmed against your interface.

You would typically only provide an interface for a class when the benefits outweigh the cost. It is good practice to provide (Java) interfaces for the public/published interfaces of components or subsystems.

Cheers,
Oliver

[mo sayed]

A little longer: First, polymorphic behavior does not depend on a class having an interface; a class hierarchy without any interface can exhibit polymorphic behavior.

Providing an interface allows you to separate the implementation of an abstraction (i.e. the class) from its interface (i.e. the interface itself). You can exchange or modify the implementation without affecting code programmed against your interface.

You would typically only provide an interface for a class when the benefits outweigh the cost. It is good practice to provide (Java) interfaces for the public/published interfaces of components or subsystems.

Sorry I should have been clearer. I did not convey the full benefits of programming to an interface. You captured this beautifully. My intent was to
determine to what extent this practice should be executed. As with most things it seems that this is a case of fine judgement. Thanks for the answer.
regards,
Mo

[Adeel Ansari]

One more important thing. Whenever you encounter this term "Programming to an interface". Don't ever just take it as Interface in Java. It can be an abstract class or sometimes a normal superclass.

Cheers.