通过Java Swing中的循环更新Jlabel文本？

Question

I want to update the Jlabel text in every second as long as the loop is running. how could I do this? I want to do as this fromat.

JPanel jpnl=new JPanel();
    jfrm.add(jpnl);
    String[] fonts=GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames();
    jlab = new JLabel("This is Label");
    jpnl.add(jlab);

        for(int i=0;i<fonts.length;i++){
            System.out.println(fonts[i]);
            jlab.setText(fonts[i]);
            jlab.setFont(new Font(fonts[i],Font.PLAIN,30));
            jlab.setForeground(Color.DARK_GRAY);
        }

Answer 1

Swing's single threaded nature precludes using a loop or Thread.sleep in the way you seem to be trying. Doing so, will simply block the UI and prevent it from been painted/updated until the loop is completed.

Because Swing is not thread safe, you can't simply use another Thread and the above approaches to update the UI, without jumping through some hoops

The conical answer to your question is to use a Swing Timer , which triggers an update at a regular bases. Because these updates are triggered within the context of the Event Dispatching Thread, it makes it safe to use when you want to update the UI.

Take a closer look at How to use Swing Timers for more details

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GraphicsEnvironment;
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 Test {

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

    public Test() {
        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 String[] fonts;
        private final JLabel jlab;
        private int index = 0;

        public TestPane() {
            setLayout(new GridBagLayout());
            fonts = GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames();
            jlab = new JLabel("This is Label");
            add(jlab);

            Timer timer = new Timer(1000, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    updateFont();
                    index++;
                    if (index >= fonts.length) {
                        ((Timer)e.getSource()).stop();
                    }
                }
            });
            timer.setInitialDelay(0);
            timer.start();
        }

        protected void updateFont() {
            System.out.println(fonts[index]);
            jlab.setText(fonts[index]);
            jlab.setFont(new Font(fonts[index], Font.PLAIN, 30));
            jlab.setForeground(Color.DARK_GRAY);           
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

    }

}