interface CallBackInterface {
  void callBackMethod();
}

interface CallBackInterface {
  void callBackMethod();
}

class CallBackClass implements CallBackInterface{

  @Override
  public void callBackMethod() {
    System.out.println("hello");
  }
}

public class CallBackTest {

  interface CallBackInterface {
    void callBackMethod();
  }

  class CallBackClass implements CallBackInterface {

    @Override
    public void callBackMethod() {
      System.out.println("hello");
    }
  }

  public void showCallBack() {
    CallBackInterface itfs = new CallBackClass();
    itfs.callBackMethod();
  }
}

public class Test {
  public static void main(String[] args) {
    new CallBackTest().showCallBack();
  }
}

public class CallBackTest {
  interface CallBackInterface {
    void callBackMethod();
  }

  class CallBackClass implements CallBackInterface {

    @Override
    public void callBackMethod() {
      System.out.println("hello");
    }
  }

  class Controller {
    private CallBackInterface cbitf;
    // 这个boolean只是为了模拟有事件，没啥实用价值
    public boolean somethingHappend;
    // 这里确实可以直接把CallBackClass做参数，而且省掉接口的定义
    // 但是这样做的话，就像是回调函数直接写在了调用函数里一样
    // 不明白的话就好好理解下"约定"和"调用者不管回调函数是怎么实现的"吧
    public Controller(CallBackInterface itfs) {
      somethingHappend = true;
      this.cbitf = itfs;
    }

    public void doSomething() {
      if(somethingHappend) {
        cbitf.callBackMethod();
      }
    }
  }

  public void showCallBack() {
    CallBackClass cbc = new CallBackClass();
    Controller ctrlr = new Controller(cbc);
    ctrlr.doSomething();
    // 其实上面也可以这样写在一行里
    // new Controller(new CallBackClass()).doSomething();
  }
}