Java While Loop检查时间但不执行方法

Question

In this code a while loop is supposed to check the time, and if the time is equal to 7 PM, then display a message box.

public void actionPerformed(ActionEvent arg0) {

    Enable.setEnabled(false);
    Date d = new Date();
    int hrs = d.getHours();
    int mins = d.getMinutes();

        while((1 + 1) == 2) { 
            if(hrs == 19 && mins == 21) {
                JOptionPane.showMessageDialog(frame,
                    "It's 7:21 PM!",
                    "Alerts",
                    JOptionPane.WARNING_MESSAGE);
                System.exit(0);
                break;
            }
        }
}

Pushing a button will do that code. If you push the button before it is 7 PM, the GUI will freeze (I don't care about that), and when it turns to 7 PM, it won't display the message box. If you click the button when it is 7 PM, then it will display the message box...

Answer 1

无需执行while（（1 + 1）== 2）来获得无限循环的方法，您可以执行以下操作：while（true）或for（;;）如果没有关于您的小时和时间的任何其他信息或代码，此问题将无法回答。分钟变量

Answer 2

You need to update hrs and mins in your loop otherwise the initialization of them, I assume at the time of pushing the button will always hold the time when the button was pushed.

This is why it works when pushed at 7pm but otherwise will not.

So do something like this

while(true) //Equivalent to what you had 
{ 
      if(hrs == 19 && mins == 00) {
           JOptionPane.showMessageDialog(frame,
               "It's 7:00 PM!",
               "Time Alert",
               JOptionPane.WARNING_MESSAGE);
           System.exit(0);
           break;
       }
       //Refresh your hrs and mins here
       Calendar calendar = GregorianCalendar.getInstance(); // Probably dont really want to actually get an instance every time
       hrs = calendar.get(Calendar.HOUR_OF_DAY);
       mins = calendar.get(Calendar.MINUTE);
}

Answer 3

I'm thinking you're using 1+1=2 to have a continuous loop. you could use while(true){...} instead. Also, the while loop wouldn't be practical for this case. There is an example on this page that does something similar (Alarm Clock): http://www.ibm.com/developerworks/java/library/j-schedule/index.html

this was their example. I updated it to suite your task.

public class AlarmClock {

    private final Scheduler scheduler = new Scheduler();
    private final SimpleDateFormat dateFormat =
        new SimpleDateFormat("dd MMM yyyy HH:mm:ss.SSS");
    private final int hourOfDay, minute, second;

    public AlarmClock() {
        this.hourOfDay = 19;
        this.minute = 0;
        this.second = 0;
    }

    public void start() {
        scheduler.schedule(new SchedulerTask() {
            public void run() {
                soundAlarm();
            }
            private void soundAlarm() {
                JOptionPane.showMessageDialog(frame,
                            "It's 7:00 PM!",
                            "Time Alert",
                            JOptionPane.WARNING_MESSAGE);
                        System.exit(0);
                // Start a new thread to sound an alarm...
            }
        }, new DailyIterator(hourOfDay, minute, second));
    }

    public static void main(String[] args) {
        AlarmClock alarmClock = new AlarmClock();
        alarmClock.start();
    }
}

Hope it helps.