public class CallBack { 
 private Callback mCallback; 
 
 public CallBack(Callback callback) { 
 this.mCallback = callback; 
 } 
 public static interface Callback { 
 public void before(); 
 public void after(); 
 } 
 
 public void doThing() { 
 mCallback.before(); 
 System.out.println("hello chenyu"); 
 mCallback.after(); 
 } 
} 

 public class TestCallBack implements CallBack.Callback{ 
 
 public CallBack mCallback; 
 
 public TestCallBack() { 
 mCallback = new CallBack(this); 
 } 
 
 @Override 
 public void before() { 
 System.out.println("hello before"); 
 } 
 
 @Override 
 public void after() { 
 System.out.println("hello before"); 
 } 
 
 public void doThing() { 
 mCallback.doThing(); 
 } 
 
 public static void main(String[] args) { 
 new TestCallBack().doThing(); 
 } 
 
} 

hello before 
hello chenyu 
hello before