Feature |
Interface |
Abstract class |
Multiple inheritance |
A class may inherit several interfaces. |
A class may inherit only one abstract class. |
Default implementation |
An interface cannot provide any code, just the signature. |
An abstract class can provide complete, default code and/or just the details that have to be overridden. |
Constants |
Only Static final constants. |
Both instance and static constants are possible. |
Core VS Peripheral |
Interfaces are used to define the peripheral abilities of a class. In other words both Human and Vehicle can inherit from a IMovable interface. |
An abstract class defines the core identity of a class and there it is used for objects of the same type. |
Homogeneity |
If the various implementations only share method signatures then it is better to use Interface. |
If the various implementations are of the same kind and use common behaviour or status then abstract class is better to use. |
Speed |
Requires more time to find the actual method in the corresponding classes. |
Fast |
Adding functionality |
If we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method. |
If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly. |