The main differences are as follows:
| Interface | Abstract Class |
|---|---|
| Used for verbs. | Used for nouns. |
| Multiple interfaces can be implemented. | Only one. |
| Even with no subtype relationship, casting is allowed. | There must be a subtype relationship for casting to work. |
Can only contain abstract methods. | Can contain abstract and non-abstract methods. |
Abstract Class
Used when a class is so general that it cannot and should not be instantiated on its own.
A Shape.
An abstract class can be considered the most generalised version in a model, where its implementation require further details to be properly implemented for its children classes.
Interface
Used to model what an entity can do, even across different class hierarchies.
GetAreable
An interface can be considered a contract - any class implementing an interface has to implement the methods in the interface.
Unlike a class, multiple interfaces can be implemented by a class, using implements .