Posted in: Core Java
- Interface is used when you only want to declare which methods and members a class MUST have. Anyone implementing the interfaca will have to declare and implement the methods listed by the interface.
- If you also want to have a default implementation, use abstract class. Any class extending the abstract class will have to implement only its abstract methods and members, and will have some default implementation of the other methods of the abstract class, which you may override or not.
- Finally, you can implement as many interfaces as you want, but only extend one class (being it abstract or not). Keep that on mind before choosing.
- Abstract class is an incomplete implementation of some concept. This incomplete implementation may be different in different context. Derived class implements the abstract class in its context.
- Interface defines contract or standard. Implementation of the interface has to follow the contract or standard. Interfaces are more used to set these types of standards or contracts.