Confusion with the Java Swing Timer [closed]

问题:

I am really confused with the Java swing timer. Does it need an action listener? Could someone please give me an example? Thanks!

回答1:

Here is an example of using javax.swing.Timer:

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class SimpleTimer extends JFrame
{
    private JLabel label;
    private Timer timer;
    private int counter = 10; // the duration
    private int delay = 1000; // every 1 second
    private static final long serialVersionUID = 1L;

    public SimpleTimer()
    {
        super("Simple Timer");
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        label = new JLabel("Wait for " + counter + " sec", JLabel.CENTER);
        JPanel contentPane = (JPanel) getContentPane();
        contentPane.add(label, BorderLayout.CENTER);
        contentPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        pack();

        ActionListener action = new ActionListener()
        {   
            @Override
            public void actionPerformed(ActionEvent event)
            {
                if(counter == 0)
                {
                    timer.stop();
                    label.setText("The time is up!");
                }
                else
                {
                    label.setText("Wait for " + counter + " sec");
                    counter--;
                }
            }
        };

        timer = new Timer(delay, action);
        timer.setInitialDelay(0);
        timer.start();

        setVisible(true);
    }

    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                new SimpleTimer();
            }
        });
    }
}

回答2:

Setting up a timer involves creating a Timer object, registering one or more action listeners on it, and starting the timer using the start method. For example, the following code creates and starts a timer that fires an action event once per second (as specified by the first argument to the Timer constructor). The second argument to the Timer constructor specifies a listener to receive the timer's action events. Timers are constructed by specifying both a delay parameter and an ActionListener. (source)

Futhermore, the timer's timing is done in thread distinct from the event dispatch thread (or EDT) which is the thread that runs the code in the ActionListener. So even if the actionPerformed code is slow, the timer will keep on firing regardless and will queue its actionPerformed code on the event queue which will likely get backed up and the event thread will get clogged and the application will be unresponsive or poorly responsive, unsell you set coalesce to true (source).

Here is a good tuturial How to Use Swing Timers