public interface Callback {
  void printFinished(String msg);
}

public class Printer {
  public void print(Callback callback, String text) {
    System.out.println("正在打印 . . . ");
    try {
      Thread.currentThread();
      Thread.sleep(3000);// 毫秒
    } catch (Exception e) {
    }
    callback.printFinished("打印完成");
  }
}

public class People {

  Printer printer = new Printer();

  /*
   * 同步回调
   */
  public void goToPrintSyn(Callback callback, String text) {
    printer.print(callback, text);
  }

  /*
   * 异步回调
   */
  public void goToPrintASyn(Callback callback, String text) {
    new Thread(new Runnable() {
      public void run() {
        printer.print(callback, text);
      }
    }).start();
  }
}

public class Main {//测试类，同步回调
  public static void main(String[] args) {
    People people = new People();
    Callback callback = new Callback() {
      @Override
      public void printFinished(String msg) {
        System.out.println("打印机告诉我的消息是 ---> " + msg);
      }
    };
    System.out.println("需要打印的内容是 ---> " + "打印一份简历");
    people.goToPrintSyn(callback, "打印一份简历");
    System.out.println("我在等待 打印机 给我反馈");
  }
}

public class Main {//异步回调
  public static void main(String[] args) {
    People people = new People();
    Callback callback = new Callback() {
      @Override
      public void printFinished(String msg) {
        System.out.println("打印机告诉我的消息是 ---> " + msg);
      }
    };
    System.out.println("需要打印的内容是 ---> " + "打印一份简历");
    people.goToPrintASyn(callback, "打印一份简历");
    System.out.println("我在等待 打印机 给我反馈");
  }
}