回調

主函數：

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.layout_main);

         B b = new B();
         b.bMothed();

    }
}

接口：

public interface Callback {
    void print(String s);
}

Class A

public class A {
    public void mothed(Callback callback) {
       callback.print("callback A");
    }
}

Class B

public class B implements Callback{

    public void bMothed() {
        A a = new A();
        a.mothed(this);
    }

    @Override
    public void print(String s) {
        Log.e("i am B",s);
    }
}