Question

从画面中心开始画点，这个点随机上下左右移动，形成如图轨迹，直到离开画面。用Java到底该怎么做？

Answer 1

import javax.swing.*;
import javax.swing.Timer;
import java.awt.*;
import java.awt.image.*;
import java.util.*;
/**
 * 面板上的光标改变成为手型
 * @author hardneedl
 */
final class RandomPointDemo extends JFrame{
    private static final Dimension SIZE = new Dimension(600,400);

    public Dimension getMinimumSize() {return SIZE;}
    public Dimension getMaximumSize() {return SIZE;}
    public Dimension getPreferredSize() {return SIZE;}

    public String getTitle() {return "RandomPointDemo";}

    /*画笔*/
    private interface Brush extends Observer {
        void paint(Graphics g);
        Component getComponent();
    }

    abstract private class PointBrush implements Brush {
        private static final int OFFSET = 2;

        private BufferedImage getImage() {
            return image;
        }

        private BufferedImage image;
        //上一次点的位置
        private int lastX, lastY;private Point newPoint;
        PointBrush(int x,int y) {
            lastX = x;lastY = y;
            image = new BufferedImage(2000,2000,BufferedImage.TYPE_INT_RGB);

        }

        public void paint(Graphics g2) {
            if (newPoint != null&&image != null) {
                g2.setColor(Color.ORANGE);
                g2.drawLine(lastX,lastY,newPoint.x,newPoint.y);

                g2.setColor(Color.MAGENTA);
                g2.fillRect(newPoint.x - OFFSET, newPoint.y - OFFSET, OFFSET<<1, OFFSET<<1);
                g2.dispose();

                lastY = newPoint.y;
                lastX = newPoint.x;
            }
        }

        public void update(Observable o, Object arg) {
            if(arg instanceof Point) {
                newPoint = (Point) arg;
                paint(image.createGraphics());
            }
        }
    }

    /*画布*/
    private class Canvas extends JComponent {
        private void setBrush(PointBrush brush) {
            this.brush = brush;
        }

        private PointBrush brush;
        private Canvas(PointBrush brush) {
            super();
            this.brush = brush;
        }

        private Canvas() {
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (isVisible()&&null!=brush) {
                Graphics2D g2 = brush.getImage().createGraphics();
                g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
                g2.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
                brush.paint(g2);
                g.drawImage(brush.getImage(),0,0,this);
            }
        }
    }
    private Timer timer;
    private Canvas canvas;
    private RandomPointDemo() {
        super();
        init();
        addListeners();
        doLay();
    }

    private void init(){
        canvas = new Canvas();
        PointBrush brush = new PointBrush(canvas.getWidth()>>1, canvas.getHeight()>>1) {

            public Component getComponent() {
                return canvas;
            }
        };

        canvas.setBrush(brush);

        timer = new Timer(500, e -> {
            Random random = new Random(System.currentTimeMillis());
            Point newPoint = new Point(
                random.nextInt(canvas.getWidth()),
                random.nextInt(canvas.getHeight())
            );
            brush.update(null, newPoint);

            canvas.paintImmediately(canvas.getBounds());
        });

        timer.start();
    }

    private void addListeners(){

    }

    private void doLay(){
        Container container = getContentPane();
        container.add(canvas, BorderLayout.CENTER);
        pack();
        setVisible(true);
    }

    public static void main(String... args) {
        System.setProperty("swing.defaultlaf","com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        SwingUtilities.invokeLater(RandomPointDemo::new);
    }
}