1、接口方法用于回调(这里定义接口是为了使用其接口方法)：

public interface ICallback {

  public void   func();

}

public class Caller {

  ICallback callback;

  public void doCallback() {

    callback.func();

  }

  public void setCallback(ICallback callback) {

    this.callback = callback;

  }

}

public class MainClass {

  public MainClass() {

  }

  public static void main(String[] args) {

    Caller caller = new Caller();

    caller.setCallback(new ICallback () {

      public void func() {

        System.out.println("dosth");

      }

    });

    caller.doCallback();

  }

}

2、向上转型

interface People{

   void peopleList();

}

class Student implements People{

   public void peopleList(){

       System.out.println("I’m a student.")；

  }

}

class Teacher implements People{

   public void peopleList(){

       System.out.println("I’m a teacher.");

   }

}

public class Example{

   public static void main(String args[]){

       People a;             //声明接口变量

       a=new Student();      //实例化，接口变量中存放对象的引用

       a.peopleList();        //接口回调

       a=new Teacher();     //实例化，接口变量中存放对象的引用

       a.peopleList();       //接口回调

  }

}

运行结果：

I’m a student.

I’m a teacher.

3、常量接口（这里不在讲）