java - 如何动态覆盖对象中的方法

Question

如果这是可能的，在创建该类的实例并希望保留对该对象的引用但在其类的定义中覆盖公共方法之后，如何更改方法的功能？

这是我的代码：

    package time_applet;

    public class TimerGroup implements Runnable{

        private Timer hour, min, sec;
        private Thread hourThread, minThread, secThread;

        public TimerGroup(){
            hour = new HourTimer();
            min = new MinuteTimer();
            sec = new SecondTimer();
        }


        public void run(){
            hourThread.start();
            minThread.start();
            secThread.start();
        }

/*Please pay close attention to this method*/
        private Timer activateHourTimer(int start_time){
            hour = new HourTimer(start_time){

                public void run(){
                    while (true){

                        if(min.changed)//min.getTime() == 0)
                            changeTime();

                    }

                }
            };
            hourThread = new Thread(hour);
            return hour;
        }

        private Timer activateMinuteTimer(int start_time){

            min = new MinuteTimer(start_time){
                public void run(){
                    while (true){

                        if(sec.changed)//sec.getTime() == 0)
                            changeTime();

                    }

                }
            };
            minThread = new Thread(min);    
            return min;
        }

        private Timer activateSecondTimer(int start_time){
            sec = new SecondTimer(start_time);
            secThread = new Thread(sec);
            return sec;
        }

        public Timer addTimer(Timer timer){
            if (timer instanceof HourTimer){
                hour = timer;
                return activateHourTimer(timer.getTime());
            }
            else if (timer instanceof MinuteTimer){
                min = timer;
                return activateMinuteTimer(timer.getTime());
            }
            else{
                sec = timer;
                return activateSecondTimer(timer.getTime());        
            }
        }
    }

因此，例如在方法 activateHourTimer() 中，我想重写小时对象的 run() 方法，而不必创建新对象。我该怎么做？

Answer 1

您不能覆盖本地（匿名）类的方法，但可以通过匿名类覆盖整个方法：

TimerGroup customTimerGroup = new TimerGroup() {
    private Timer activateHourTimer(int start_time) {
        hour = new HourTimer(start_time){ 
            public void run() {
                // do something different
            }
        };
        hourThread = new Thread(hour);
        return hour;
    }
};

Answer 2

不，您不能在同一个类中多次覆盖相同的方法，并且您正在创建一个 HourTimer 的匿名类。

      hour = new HourTimer(start_time){

            public void run(){
                while (true){

                    if(min.changed)//min.getTime() == 0)
                        changeTime();

                }

            }
        };

您可以通过在activateHourTimer方法中放置一个if else条件作为fallows-以另一种方式做到这一点-

     private Timer activateHourTimer(int start_time){
       if(Condition1){
           hour = new HourTimer(start_time){

              public void run(){
                  while (true){

                      //First Condition
                  }

              }
          };
       }else if(Condition2){
           hour = new HourTimer(start_time){

              public void run(){
                  while (true){

                      //Second Condition
                  }

              }
          };
       }else{
           hour = new HourTimer(start_time){

              public void run(){
                  while (true){

                      //Third Condition
                  }

              }
          };
       }
        hourThread = new Thread(hour);
        return hour;
    }