异步回调

A请求B，B处理后再通知A

public interface ICallback {    public void callback();}

public class CallbackImpl implements ICallback {    @Override    public void callback() {        System.out.println("callbackimpl");    }    public static void main(String[] args) {        Caller caller = new Caller(new CallbackImpl());        caller.call();    }}

public class Caller {        private ICallback callback;    public Caller(ICallback callback) {        this.callback = callback;    }        public void call(){        this.callback.callback();    }}