Java applet重新绘制一个移动的圆圈

Question

我刚从Pygame搬过来,所以applet中的Java 2D对我来说有点新鲜,特别是在重新绘制屏幕时.在pygame中你可以简单地做,display.fill([1,1,1])但我如何在Java中的applet中执行此操作？我理解使用repaint()但不清除屏幕 - 任何移动的物体都没有从屏幕上"移除",所以你只需要画出一长串画圆.

这是我一直在测试的代码:

package circles;
import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.util.Random;

public class circles extends Applet implements Runnable {
    private static final long serialVersionUID = -6945236773451552299L;
    static Random r = new Random();

    String msg = "Click to play!";
    static int w = 800, h = 800;

    int[] txtPos = { (w/2)-50,(h/2)-50 };
    int[] radiusRange = { 5,25 };
    int[] circles;
    static int[] posRange;

    int x = 0, y = 0;
    int radius = 0;
    int cursorRadius = 10;

    boolean game = false;

    public static int[] pos() {
        int side = r.nextInt(5-1)+1;
        switch(side) {
            case 1:
                posRange = new int[]{ 1,r.nextInt(w),r.nextInt((h+40)-h)+h,r.nextInt(270-90)+90 };
                break;
            case 2:
                posRange = new int[]{ 2,r.nextInt((w+40)-w)+w,r.nextInt(h),r.nextInt(270-90)+90 };
                break;
            case 3:
                posRange = new int[]{ 3,r.nextInt(w),r.nextInt(40)-40,r.nextInt(180) };
                break;
            case 4:
                posRange = new int[]{ 4,r.nextInt(40)-40,r.nextInt(h),r.nextInt(180) };
                break;
        }
        System.out.println(side);
        return posRange;
    }
    public void start() {
        setSize(500,500);
        setBackground(Color.BLACK);
        new Thread(this).start();
    }

    public void run() {

    }
    public void update(Graphics g) {
        paint(g);
    }

    public void paint(Graphics e) {
        Graphics2D g = (Graphics2D) e;

        if(System.currentTimeMillis()%113==0) {
            x+=1;
            y+=1;
        }

        g.setColor(Color.BLUE);
        g.fillOval(x,y,20,20);

        repaint();
    }
}

Answer 1

1. 你需要调用super.paint(g);你的paint方法,以免留下油漆文物.

2. 永远不要repaint()从paint方法内部打电话

3. 当你打算打电话时paint,不要像你一样明确update()地打电话reapaint()

4. 只需从方法内部更新x和y值update(),然后调用repaint()

5. 你不需要参加Graphics辩论update()

6. 你需要update()在一个循环中反复调用某个地方,因为它会更新xand y和reapint()s

7. 如果你的班级是a Runnable,那么你应该在run()方法中加入一些代码.这可能就是你应该拥有循环的地方

import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;

public class circles extends Applet implements Runnable {

    int x = 0, y = 0;

    public void start() {
        setSize(500, 500);
        setBackground(Color.BLACK);
        new Thread(this).start();
    }

    public void run() {
        while (true) {
            try {
                update();
                Thread.sleep(50);

            } catch (InterruptedException ex) {

            }
        }
    }

    public void update() {
        x += 5;
        y += 6;
        repaint();
    }

    public void paint(Graphics e) {
        super.paint(e);
        Graphics2D g = (Graphics2D) e;
        g.setColor(Color.BLUE);
        g.fillOval(x, y, 20, 20);

    }
}

附注

• 为什么首先使用Applet.如果必须,为什么要使用AWT Applet而不是Swing JApplet？升级的时间.

这是我在Swing中重做整个事情的方法,使用Swing Timer而不是循环Thread.sleep,就像你应该做的那样.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class Circle extends JPanel{
    private static final int D_W = 500;
    private static final int D_H = 500;

    int x = 0;
    int y = 0;
    public Circle() {
        setBackground(Color.BLACK);

        Timer timer = new Timer(50, new ActionListener(){
            public void actionPerformed(ActionEvent e) {
                x += 5;
                y += 5;
                repaint();
            }
        });
        timer.start();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.BLUE);
        g.fillOval(x, y, 20, 20);

    }

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

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new Circle());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

• 请参见如何使用Swing Timers

• 请参阅使用Swing创建GUI

• 这是更高级的例子供您查看和思考.

UPDATE

"问题是,这是一个JPANEL应用程序.我特别希望在网页上轻松使用applet."

你仍然可以使用它.只需使用JPanel.取出main方法,而不是Applet,使用JApplet,只需将JPanel添加到您的applet.很简单.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
import javax.swing.JPanel;
import javax.swing.Timer;

public class CircleApplet extends JApplet {

    @Override
    public void init() {
        add(new Circle());
    }

    public class Circle extends JPanel {

        private static final int D_W = 500;
        private static final int D_H = 500;

        int x = 0;
        int y = 0;

        public Circle() {
            setBackground(Color.BLACK);

            Timer timer = new Timer(50, new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    x += 5;
                    y += 5;
                    repaint();
                }
            });
            timer.start();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.BLUE);
            g.fillOval(x, y, 20, 20);

        }

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

    }
}