Partial interface Implementations

If a class implements an interface but does not fully implement its methods, then that class must be declared as abstract. For example:

 
interface MyInterface {
  void callback(int param);

  void show();
}

abstract class Incomplete implements MyInterface {
  int a, b;

  public void show() {
    System.out.println(a + " " + b);
  }

}

1. What is a Java Interface
2. Implementing Interfaces
3. Accessing Implementations Through Interface References
4. Partial interface Implementations
5. Variables in Interfaces
6. Interfaces Can Be Extended