Difference Between Interface and Abstract Class

Difference Between Interface and Abstract Class

1. Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior.
2. Java interface should be implemented using keyword “implements”; A Java abstract class should be extended using keyword “extends”.
3. An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces.
4. Interface is absolutely abstract and cannot be instantiated; A Java abstract class also cannot be instantiated, but can be invoked if a main() exists.
5. In comparison with java abstract classes, java interfaces are slow as it requires extra indirection.
6. Members of a Java interface are public by default. A Java abstract class can have the usual flavors of class members like private, protected, etc..
7. A Java class can implement multiple interfaces but it can extend only one abstract class