在小程序上显示旋转的风扇

Question

作为我的编程任务的一部分，我必须在小程序中显示一个旋转的风扇。

这是我的代码（显示风扇的类）：

import javax.swing.*;
import java.awt.*;

public class Fan extends JPanel
{
    private int angle1 = -15;
    private int angle2 = 75;
    private int angle3 = 165;
    private int angle4 = 255;

    public Fan()
    {
        this.setSize(600, 400);
        Runnable spinner = new SpinFan();

        Thread thread1 = new Thread(spinner);
        thread1.start();
    }


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

        g.drawOval(200, 150, 150, 150);
        g.fillArc(210, 160, 130, 130, angle1, 30);
        g.fillArc(210, 160, 130, 130, angle2, 30);
        g.fillArc(210, 160, 130, 130, angle3, 30);
        g.fillArc(210, 160, 130, 130, angle4, 30);
    }
}

class SpinFan implements Runnable
{
    @Override
    public void run() 
    {
        try
        {
            while(true)
            {
                angle1 = (angle1 + 1) % 360;
                angle2 = (angle2 + 1) % 360;
                angle3 = (angle3 + 1) % 360;
                angle4 = (angle4 + 1) % 360;

                System.out.println(angle1 + " " + angle2 + " " + angle3 + " " + angle4);

                repaint();

                Thread.sleep(10);
            }
        }
        catch(InterruptedException ex)
        {
            System.out.println("Problem while putting thread to sleep.");
        }
    }
}

用于进一步处理的类（现在只有 Fan 的实例）：

import java.awt.*;
import javax.swing.*;

public class FanControl extends JPanel
{
    public FanControl()
    {
        add(new Fan());
    }
}

最后，这是 Applet 类：

import java.awt.*;
import javax.swing.*;

public class FanApplet extends JApplet
{   
    public FanApplet()
    {
        add(new FanControl());
    }
}

现在我已经尝试了很长时间了，所以请不要介意额外注释掉的代码。 Fan.java 类工作正常（如果我将它作为应用程序运行，将它放在框架中，我可以看到风扇在旋转）。但我就是无法让风扇在 Applet 中旋转。但是，如果我从 Fan.java 类向 Applet 添加类似 JButton 的东西，它就可以工作。

我错过了什么？使用线程和小程序，或paintComponent() 和我似乎不知道的小程序时是否有一些并发症。

当我将代码作为应用程序运行时，它运行良好。我可以看到旋转的风扇。这是代码：

import javax.swing.*;
import java.awt.*;

public class Fan extends JPanel
{
private int angle1 = -15;
private int angle2 = 75;
private int angle3 = 165;
private int angle4 = 255;

public Fan()
{
    Runnable spinner = new SpinFan();

    Thread thread1 = new Thread(spinner);
    thread1.start();
}


public static void main(String[] args)
{   
    JFrame frame = new JFrame();
    frame.add(new Fan());
    frame.setSize(600, 400);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
}


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

    g.drawOval(200, 150, 150, 150);
    g.fillArc(210, 160, 130, 130, angle1, 30);
    g.fillArc(210, 160, 130, 130, angle2, 30);
    g.fillArc(210, 160, 130, 130, angle3, 30);
    g.fillArc(210, 160, 130, 130, angle4, 30);

}

class SpinFan implements Runnable
{
    @Override
    public void run() 
    {
        try
        {
            while(true)
            {
                angle1 = (angle1 - 1) % 360;
                angle2 = (angle2 - 1) % 360;
                angle3 = (angle3 - 1) % 360;
                angle4 = (angle4 - 1) % 360;

                System.out.println(angle1 + " " + angle2 + " " + angle3 + " " + angle4);

                repaint();

                Thread.sleep(10);
            }
        }

        catch(InterruptedException ex)
        {
            System.out.println("Problem while putting thread to sleep.");
        }
    }

}
}

Answer 1

while(true) .. repaint(); .. Thread.sleep(10);

这完全是错误的动画制作方式。

不要阻塞 EDT（事件调度线程）——当这种情况发生时，GUI 将“冻结”。而不是调用 Thread.sleep(n) 实现 Swing Timer 用于重复任务或 SwingWorker 用于长时间运行的任务。有关详细信息，请参阅Concurrency in Swing。

以下源使用代码中定义的Thread，但将 GUI 更新放回 EDT。

但这里真正的问题是动画组件被添加到大小为 0x0 的小程序中。通过将父容器的布局更改为BorderLayout，我们可以拉伸它以适应可用空间。

例如

import java.awt.*;
import javax.swing.*;

public class FanApplet extends JApplet
{
    private int angle1 = -15;
    private int angle2 = 75;
    private int angle3 = 165;
    private int angle4 = 255;

    public FanApplet()
    {
        add(new FanControl());
    }

    class FanControl extends JPanel
    {
        public FanControl()
        {
            // by setting a BorderLayout and adding a component to the CENTER
            // (default if no constraint specified) the child component will
            // be stretched to fill the available space.
            setLayout(new BorderLayout());
            add(new Fan());
        }
    }

    class Fan extends JPanel
    {
        public Fan()
        {
            //this.setSize(600, 400);
            Runnable spinner = new SpinFan();

            Thread thread1 = new Thread(spinner);
            thread1.start();
        }


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

            g.drawOval(200, 150, 150, 150);
            g.fillArc(210, 160, 130, 130, angle1, 30);
            g.fillArc(210, 160, 130, 130, angle2, 30);
            g.fillArc(210, 160, 130, 130, angle3, 30);
            g.fillArc(210, 160, 130, 130, angle4, 30);
        }
    }

    class SpinFan implements Runnable
    {
        @Override
        public void run()
        {
            try
            {
                while(true)
                {
                    angle1 = (angle1 + 1) % 360;
                    angle2 = (angle2 + 1) % 360;
                    angle3 = (angle3 + 1) % 360;
                    angle4 = (angle4 + 1) % 360;

                    System.out.println(angle1 + " " + angle2 + " " + angle3 + " " + angle4);

                    // This ensures that repaint() is called on the EDT.
                    Runnable r = new Runnable() {
                        public void run() {
                            repaint();
                        }
                    };
                    SwingUtilities.invokeLater(r);

                    Thread.sleep(10);
                }
            }
            catch(InterruptedException ex)
            {
                System.out.println("Problem while putting thread to sleep.");
            }
        }
    }
}