如何解决时钟闪烁？

Question

我目前正在使用 AWT Package 和 Swing 在 java 中制作模拟时钟。但是数字时钟覆盖目前每隔一段时间就闪烁一次，我想解决这个问题。

我读过有关与 repaint() 一起实现双缓冲的内容，但我对如何实现它一头雾水。


import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;
import java.util.Timer;
import java.util.TimerTask;
import javax.swing.JFrame;

public class Clock2d extends Applet {

    GregorianCalendar cal;
    Timer clockTimer = new Timer();
    TimeZone clockTimeZone = TimeZone.getDefault();

    public Clock2d() {
        clockTimer.schedule(new TickTimerTask(), 0, 1000);
    }

    @Override
    public void init() {
    }

    public void paint(Graphics g) {
        g.setColor(Color.BLUE);
        g.fillOval(40, 40, 220, 220);
        g.setColor(Color.WHITE);
        g.fillOval(50, 50, 200, 200);

        double second = cal.get(Calendar.SECOND);
        double minute = cal.get(Calendar.MINUTE);
        double hours = cal.get(Calendar.HOUR);

        for (int i = 0; i < 60; i++) {
            int length = 90;
            double rad = (i * 6) * (Math.PI) / 180;
            if (i % 5 == 0) {
                length = 82;
                g.setColor(Color.BLUE);
            } else {
                g.setColor(Color.GRAY);
            }
            int x = 150 + (int) (95 * Math.cos(rad - (Math.PI / 2)));
            int y = 150 + (int) (95 * Math.sin(rad - (Math.PI / 2)));
            int x1 = 150 + (int) (length * Math.cos(rad - (Math.PI / 2)));
            int y1 = 150 + (int) (length * Math.sin(rad - (Math.PI / 2)));
            g.drawLine(x, y, x1, y1);
        }

        drawHands(g, second, minute, hours);

        SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss");
        g.setColor(Color.BLUE);
        g.setFont(new Font("Tahoma", Font.BOLD, 16));
        g.drawString(sdf.format(cal.getTime()), 120, 20);
        g.setFont(new Font("Arial", Font.BOLD, 10));

    }

    public void drawHands(Graphics g, double second, double minute, double hours) {
        double rSecond = (second * 6) * (Math.PI) / 180;
        double rMinute = ((minute + (second / 60)) * 6) * (Math.PI) / 180;
        double rHours = ((hours + (minute / 60)) * 30) * (Math.PI) / 180;
        g.setColor(Color.RED);
        g.drawLine(150, 150, 150 + (int) (100 * Math.cos(rSecond - (Math.PI / 2))), 150 + (int) (100 * Math.sin(rSecond - (Math.PI / 2))));
        g.setColor(Color.BLACK);
        g.drawLine(150, 150, 150 + (int) (70 * Math.cos(rMinute - (Math.PI / 2))), 150 + (int) (70 * Math.sin((rMinute - (Math.PI / 2)))));
        g.drawLine(150, 150, 150 + (int) (50 * Math.cos(rHours - (Math.PI / 2))), 150 + (int) (50 * Math.sin(rHours - (Math.PI / 2))));
    }

    class TickTimerTask extends TimerTask {

        @Override
        public void run() {

            cal = (GregorianCalendar) GregorianCalendar.getInstance(clockTimeZone);
            repaint();
        }
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Clock 2D");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(330, 330));
        Clock2d clock2d = new Clock2d();
        clock2d.setPreferredSize(new Dimension(320, 320));
        clock2d.init();
        frame.setLayout(new BorderLayout());
        frame.getContentPane().add(clock2d, BorderLayout.CENTER);
        frame.pack();
        frame.setVisible(true);
    }
}

除了编号数字时钟偶尔闪烁之外，代码完全按预期工作。

Answer 1

public class Clock2d extends Applet 一个 java.awt.Applet 不仅被弃用，而且默认情况下也没有双缓冲。更改它以扩展 JPanel（即）。
然后将public void paint(Graphics g) {更改为public void paintComponent(Graphics g) { super.paintComponent(g);以尊重油漆链。
class TickTimerTask extends TimerTask 改用 javax.swing.Timer。它在事件调度线程上运行，对 GUI 的任何调用都应在 EDT 上进行。

代码中表达了这三点。你看到这个版本中的 'flickering' 工件了吗？

import java.awt.*;
import java.awt.event.*;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;
import javax.swing.*;

public class Clock2d extends JPanel {

    TimeZone clockTimeZone = TimeZone.getDefault();
    GregorianCalendar cal = 
            (GregorianCalendar) GregorianCalendar.getInstance(clockTimeZone);
    ActionListener repaintListener = (ActionEvent e) -> {
        cal = (GregorianCalendar) GregorianCalendar.getInstance(clockTimeZone);
        repaint();
    };
    Timer clockTimer = new Timer(100, repaintListener);

    public Clock2d() {
        clockTimer.start();
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.BLUE);
        g.fillOval(40, 40, 220, 220);
        g.setColor(Color.WHITE);
        g.fillOval(50, 50, 200, 200);

        double second = cal.get(Calendar.SECOND);
        double minute = cal.get(Calendar.MINUTE);
        double hours = cal.get(Calendar.HOUR);

        for (int i = 0; i < 60; i++) {
            int length = 90;
            double rad = (i * 6) * (Math.PI) / 180;
            if (i % 5 == 0) {
                length = 82;
                g.setColor(Color.BLUE);
            } else {
                g.setColor(Color.GRAY);
            }
            int x = 150 + (int) (95 * Math.cos(rad - (Math.PI / 2)));
            int y = 150 + (int) (95 * Math.sin(rad - (Math.PI / 2)));
            int x1 = 150 + (int) (length * Math.cos(rad - (Math.PI / 2)));
            int y1 = 150 + (int) (length * Math.sin(rad - (Math.PI / 2)));
            g.drawLine(x, y, x1, y1);
        }

        drawHands(g, second, minute, hours);

        SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss");
        g.setColor(Color.BLUE);
        g.setFont(new Font("Tahoma", Font.BOLD, 16));
        g.drawString(sdf.format(cal.getTime()), 120, 20);
        g.setFont(new Font("Arial", Font.BOLD, 10));

    }

    public void drawHands(Graphics g, double second, double minute, double hours) {
        double rSecond = (second * 6) * (Math.PI) / 180;
        double rMinute = ((minute + (second / 60)) * 6) * (Math.PI) / 180;
        double rHours = ((hours + (minute / 60)) * 30) * (Math.PI) / 180;
        g.setColor(Color.RED);
        g.drawLine(150, 150, 150 + (int) (100 * Math.cos(rSecond - (Math.PI / 2))), 150 + (int) (100 * Math.sin(rSecond - (Math.PI / 2))));
        g.setColor(Color.BLACK);
        g.drawLine(150, 150, 150 + (int) (70 * Math.cos(rMinute - (Math.PI / 2))), 150 + (int) (70 * Math.sin((rMinute - (Math.PI / 2)))));
        g.drawLine(150, 150, 150 + (int) (50 * Math.cos(rHours - (Math.PI / 2))), 150 + (int) (50 * Math.sin(rHours - (Math.PI / 2))));
    }

    public static void main(String[] args) {
        // Swing / AWT GUIs should be created & changed on the EDT ..
        Runnable r = () -> {
            JFrame frame = new JFrame("Clock 2D");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setPreferredSize(new Dimension(330, 330));
            Clock2d clock2d = new Clock2d();
            clock2d.setPreferredSize(new Dimension(320, 320));
            frame.setLayout(new BorderLayout());
            frame.getContentPane().add(clock2d, BorderLayout.CENTER);
            frame.pack();
            frame.setVisible(true);
        };
        // .. this is how we ensure that Runnable is on the EDT.
        SwingUtilities.invokeLater(r);
    }
}

进一步提示字体：

g.setFont(new Font("Arial", Font.BOLD, 10));

鉴于重复调用paint方法，最好在构造class时建立字体（两者）并将它们存储在class的属性中（可以在方法中被引用）。

但最好使用逻辑字体而不是像 'Arial' 这样的字体：

g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 10));

这不仅提供编译时检查，而且适用于 OS 平台。例如，SANS_SERIF 字体在 Windows 和大多数 *nix 框上会导致 Arial，但在 OS X 上默认的 SANS_SERIF（未修饰）字体是 Helvetica。

另一种字体 Tahoma 的问题更大。同样，它可能出现在许多 Windows 盒子上，但最好对其进行测试并拥有备份列表，或者为时钟应用程序提供字体。（假设您有发行权）。

如何解决时钟闪烁？

How to fix the clock from flickering?

java

swing

awt