时间不重绘的Applet [英] Time doesn't repaint in Applet

问题描述

我有一个小问题，但我不知道要修复它。我创建简单的小程序应该是简单的数字时钟。我创建了所有的方法正确，但重绘方法不重绘我的小程序。你可以检查我的code和说得清是错误的。谢谢你。

 公共类DigitalClock扩展JApplet的实现Runnable {私人螺纹timeThread;
日期日期=新的日期（）;公共无效的start（）{
    timeThread =新主题（这一点，时钟）;
    timeThread.start（）;
}@覆盖
公共无效停止（）{
    如果（timeThread == NULL）{
        返回;
    }
    timeThread = NULL;
}@覆盖
公共无效的run（）{
    而（timeThread！= NULL）{
        重绘（）;
        尝试{
            timeThread.sleep（1000）;
        }赶上（InterruptedException的E）{
        }
    }
}@覆盖
公共无效漆（图形G）{
    date.setTime（System.currentTimeMillis的（））;
    g.drawString（与Date.toString（），50，95）;
}
}
 

解决方案

只需使用 javax.swing.Timer中的。 了解如何使用Swing定时器

下面是一个例子。但是，而不是在顶层容器油画般 JApplet的你是干什么的，我画上的JP​​anel 这是比较推荐

 进口java.awt中的*。
java.awt.event中导入*。
进口java.text.SimpleDateFormat的;
进口java.util.Date;
进口的javax.swing *。公共类TimerPanel继承JPanel {    私人字符串dateString;
    私人最终的SimpleDateFormat格式;
    私人最终字体字库;
    私人最终日期日期;    公共TimerPanel（）{
        格式=新的SimpleDateFormat（HH：MM：SS）;
        字体=新的字体（影响，Font.PLAIN，30）;
        日期=新的日期（）;        date.setTime（System.currentTimeMillis的（））;
        dateString = format.format（日期）;        定时器定时器=新定时器（1000，新的ActionListener（）{
            @覆盖
            公共无效的actionPerformed（ActionEvent的五）{
                date.setTime（System.currentTimeMillis的（））;
                dateString = format.format（日期）;
                重绘（）;
            }
        }）;
        timer.start（）;
    }    @覆盖
    保护无效paintComponent（图形G）{
        super.paintComponent方法（G）;        g.setFont（字体）;
        FontMetrics对象FM = g.getFontMetrics（字体）;
        INT宽度= fm.stringWidth（dateString）;
        INT高度= fm.getAscent（）;
        INT X =的getWidth（）/ 2  - 宽/ 2;
        INT Y =的getHeight（）/ 2 +高/ 2;        g.drawString（da​​teString，X，Y）;
    }    @覆盖
    公共尺寸的get preferredSize（）{
        返回新尺寸（300，100）;
    }    公共静态无效的主要（字串[] args）{
        SwingUtilities.invokeLater（Runnable的新（）{
            @覆盖
            公共无效的run（）{
                TimerPanel定时器=新TimerPanel（）;
                JOptionPane.showMessageDialog（
                        空，定时器，数字时钟，JOptionPane.PLAIN_MESSAGE）;
            }
        }）;
    }
}
 

---

更直接地回答你的问题，你的code工作时，我测试了一下，你忘了这样做的唯一的事情就是调用 super.paint（）。按预期这样做之后，

  @覆盖
公共无效漆（图形G）{
    super.paint（G）;
 

您会希望避免视频下载虽然。您可能会注意到这会导致闪烁。这是pferred使用 javax.swing.Timer中的 $ P $。这就是为什么我用我的示例首先回答。

I have a small problem but I don't know to fix it. I create simple Applet in which should be simple digital clock. I created all methods correctly but repaint methods doesn't repaint my applet. Can you check my code and say where is mistake. Thanks.

public class DigitalClock extends JApplet implements Runnable {

private Thread timeThread;
Date date = new Date();

public void start() {
    timeThread = new Thread(this, "Clock");
    timeThread.start();
}

@Override
public void stop() {
    if (timeThread == null) {
        return;
    }
    timeThread = null;
}

@Override
public void run() {
    while (timeThread != null) {
        repaint();
        try {
            timeThread.sleep(1000);
        } catch (InterruptedException e) {
        }
    }
}

@Override
public void paint(Graphics g) {
    date.setTime(System.currentTimeMillis());
    g.drawString(date.toString(), 50, 95);
}
}

解决方案

Just use a javax.swing.Timer. See how to use Swing Timer

Here's an example. But rather than painting on top-level container like JApplet which you are doing, I'm painting on JPanel which is more recommended

import java.awt.*;
import java.awt.event.*;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.swing.*;

public class TimerPanel extends JPanel {

    private String dateString;
    private final SimpleDateFormat format;
    private final Font font;
    private final Date date;

    public TimerPanel() {
        format = new SimpleDateFormat("hh:mm:ss a");
        font = new Font("impact", Font.PLAIN, 30);
        date = new Date();

        date.setTime(System.currentTimeMillis());
        dateString = format.format(date);

        Timer timer = new Timer(1000, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                date.setTime(System.currentTimeMillis());
                dateString = format.format(date);
                repaint();
            }
        });
        timer.start();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        g.setFont(font);
        FontMetrics fm = g.getFontMetrics(font);
        int width = fm.stringWidth(dateString);
        int height = fm.getAscent();
        int x = getWidth() / 2 - width / 2;
        int y = getHeight() / 2 + height / 2;

        g.drawString(dateString, x, y);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 100);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                TimerPanel timer = new TimerPanel();
                JOptionPane.showMessageDialog(
                        null, timer, "Digital Clock", JOptionPane.PLAIN_MESSAGE);
            }
        });
    }
}

---

More directly answering your question, your code works when I test it, the only thing you're forgetting to do is call super.paint(). Works as expected after doing so

@Override
public void paint(Graphics g) {
    super.paint(g);

You'll want to avoid Thread.sleep though. You may notice this causes flickering. It's preferred to use javax.swing.Timer. That's why I answered with my example first.

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