这个计时器有什么问题？ [英] What is wrong with this timer?

问题描述

我正在做一个定时器，将90秒的时间一直递减到零，但是当我运行它时，它将运行1秒钟并终止，请帮助！指出问题所在！

I am doing a timer to countdown fro 90 seconds all the way down to zero, however when i run it, it will run for 1 second and terminate, plz help! Point out what is wrong!

package TestingFile;

import javax.swing.*;
import javax.swing.event.*;

import java.awt.*;
import java.awt.event.*;


public class TestingATimer extends JFrame
{
    private Timer timer;
    public int count = 90;

    public TestingATimer()
    {
        timer = new Timer(1000, new TimerListener());
        timer.start();
    }

    private class TimerListener implements ActionListener
    {
        public void actionPerformed (ActionEvent e)
        {
            if (count != 0)
            {   
            count--;
            System.out.println(count + " seconds elapsed"); 
            }
        }

    }

    public static void main (String [] args)
    {
        new TestingATimer ();
    }
}

推荐答案

（摆动） Timer 可能使用基于 daemon 的线程。这意味着一旦 main 方法存在，就没有什么可以阻止JVM终止...

The (Swing) Timer is likely using a daemon based thread. This means that once the main method exists, there is nothing keeping the JVM from terminating...

Thread JavaDocs

From the Thread JavaDocs

Java虚拟机启动时，通常只有一个
非守护线程（通常会调用某些
指定类的名为main的方法）。 Java虚拟机将继续执行
线程，直到发生以下任何一种情况为止：

When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls the method named main of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:

• 已调用Runtime类的退出方法并且安全
  经理已允许进行退出操作。


• 不是守护程序线程的所有线程
  都已死亡，方法是从
  调用返回到run方法，或者引发传播
  的异常

因此没有什么可以阻止JVM终止。

So there is nothing stopping the JVM from terminating.

问题是，为什么要使用没有GUI的 javax.swing.Timer ？您要达到什么目的？

The question is, why are you using a javax.swing.Timer without a GUI? What are you trying to achieve?

已更新

如果不这样做想要使用GUI，您将需要使用 java.util.Timer ，例如...

If you don't want to use a GUI, you will need to use a java.util.Timer, for example...

import java.util.Timer;
import java.util.TimerTask;

public class Clock {

    private static Timer timer;

    public static void main(String[] args) {

        timer = new Timer();
        timer.scheduleAtFixedRate(new TickTask(), 0, 1000);

    }

    public static class TickTask extends TimerTask {

        private boolean started = false;
        private long startTime = 0;

        @Override
        public void run() {
            if (!started) {
                started = true;
                startTime = System.currentTimeMillis();
            } else {
                long dif = System.currentTimeMillis() - startTime;
                long seconds = dif / 1000;
                System.out.println(seconds);
                if (seconds >= 90) {
                    timer.cancel();
                }
            }
        }

    }

}

否则，您需要提供某种GUI ...

Otherwise you'll need to supply some kind GUI...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class ClockGUI {

    public static void main(String[] args) {
        new ClockGUI();
    }

    public ClockGUI() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Timer timer;
        private JLabel clock;

        public TestPane() {
            setLayout(new GridBagLayout());
            clock = new JLabel("...");
            add(clock);
            timer = new Timer(1000, new ActionListener() {

                private boolean started = false;
                private long startTime = 0;

                @Override
                public void actionPerformed(ActionEvent e) {
                    if (!started) {
                        started = true;
                        startTime = System.currentTimeMillis();
                    } else {
                        long dif = System.currentTimeMillis() - startTime;
                        long seconds = dif / 1000;
                        clock.setText(Long.toString(seconds));
                        if (seconds >= 90) {
                            timer.stop();
                        }
                    }
                }
            });
            timer.start();
        }

    }

}

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