After knowing what is an abstract class and interface in Java, let us summarize their differences. The differences Abstract class vs Interface given in a table format, at a single place, gives more clarity for a novice, attempting to learn Java.
Table on Abstract class vs Interface
| Abstract class | Interface |
|---|---|
| Supports multilevel and hierarchical inheritance but "not multiple inheritance" (main difference) | Supports all types of inheritances – multilevel, hierarchical and multiple. |
| Can contain concrete methods also apart abstract methods(important difference) | Must contain only abstract methods |
| Use "extends" keyword to inherit | "implements" keyword should be used |
| Access specifier of an abstract method can be any one except private | Access specifier must be public only |
| Access specifier like public and access modifier abstract should be mentioned | All the methods must be public and abstract and if omitted, taken by default |
| When few methods are to be given functionality, choose abstract class | When all the methods should not be given functionality, choose interfaces |
| Variables may be of any access specifier including private | Variables must be public, static and final; and if omitted, taken by default |
| One abstract class cannot extend more than one abstract class | One interface can extend more than one interface |
| Can have constructors | Can not have constructors |
Common functionalities (or similarities)
1. With the both, we cannot create objects but reference variables can be created.
2. Both support dynamic polymorphism.
Class vs Interface is also available.
