想借鉴一下仁兄的画图程序，类似于windows的画板或Image.

Question

package study;import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Vector;public class DrawShape extends JFrame implements ActionListener {
    private static final int line = 0;
    private static final int circle = 1;
    private int curType;
    private Graphics g;
    private JPanel mainPanel = new JPanel(new BorderLayout());
    private JPanel shapePanel = new ShapePanel();
    private JScrollPane scrollPane = new JScrollPane();
    private JToolBar controlBar = new JToolBar(JToolBar.VERTICAL);
    private JFrame thisFrame;    private static final Object[][] CommAndData = {
        {"Line", "Circle", "Black", "Red", "Yellow", "Blue"},
        {new Integer(line), new Integer(circle), Color.black, Color.red, Color.yellow, Color.blue}
    };
    private JToggleButton[] shapeArra = {
        new JToggleButton("Line"), new JToggleButton("Circle")
    };
    private JToggleButton[] colorArra = {
        new JToggleButton("Black"), new JToggleButton("Red"), new JToggleButton("Yellow"), new JToggleButton("Blue")
    };    private Point startPoint = new Point(), endPoint = new Point();
    private Color curColor = shapePanel.getForeground();
    private Vector actionBuf = new Vector(100);
    private boolean flag = true;    public DrawShape() {
        thisFrame = this;
        this.setResizable(true
        ButtonGroup groupShape = new ButtonGroup();
        ButtonGroup groupColor = new ButtonGroup();
        for (int i = 0; i < shapeArra.length; i++) {
            groupShape.add(shapeArra[i]);
            shapeArra[i].addActionListener(this);
        }
        for (int i = 0; i < colorArra.length; i++) {
            groupColor.add(colorArra[i]);
            colorArra[i].addActionListener(this);
        }        controlBar.setFloatable(false);
        for (int i = 0; i < shapeArra.length; i++) {
            if (i == 0) {
                shapeArra[i].setSelected(true);
                curType = ((Integer) CommAndData[1][0]).intValue();
                //study tooltip delay time
                shapeArra[i].addMouseListener(new MouseAdapter() {
                    ToolTipManager tip = ToolTipManager.sharedInstance();
                    int oldIniDelay = 750, oldDisDelay = 4000;                    public void mouseEntered(MouseEvent e) {
                        oldIniDelay = tip.getInitialDelay();
                        oldDisDelay =  tip.getDismissDelay();
                        tip.setInitialDelay(750);
                        tip.setDismissDelay(50000);
                    }                    public void mouseExited(MouseEvent e) {
                        tip.setInitialDelay(oldIniDelay);
                        tip.setDismissDelay(oldDisDelay);
                    }
                });
            }
            shapeArra[i].setToolTipText("tooltip");
            controlBar.add(shapeArra[i]);
            shapeArra[i].setFocusPainted(false);
            shapeArra[i].setActionCommand((String) CommAndData[0][i]);
        }
        controlBar.addSeparator();
        for (int i = 0; i < colorArra.length; i++) {
            controlBar.add(colorArra[i]);
            colorArra[i].setFocusPainted(false);
            colorArra[i].setActionCommand((String) CommAndData[0][i + shapeArra.length]);
        }        scrollPane.setViewportView(shapePanel);        mainPanel.add(controlBar, BorderLayout.WEST);
        mainPanel.add(scrollPane, BorderLayout.CENTER);        this.getContentPane().add(mainPanel);        shapePanel.setBackground(Color.white);
        shapePanel.addMouseListener(new MyMouseListener());
        shapePanel.addMouseMotionListener(new MyMouseMotion());        this.addWindowListener(new WindowAdapter() {
            public void windowDeiconified(WindowEvent e) {
                System.out.println("Deiconified");
                if (g == null) {
                    g = shapePanel.getGraphics();
                }
//                refresh(g);
            }
            
            public void windowIconified(WindowEvent e) {
                System.out.println("Iconified");
                thisFrame.toFront();
            }
        });        this.setSize(800, 600);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }    public void actionPerformed(ActionEvent e) {
        for (int i = 0; i < CommAndData[0].length; i++) {
             if (((String) CommAndData[0][i]).equals(e.getActionCommand())) {
                 if (Integer.class.isInstance(CommAndData[1][i])) {
                     curType = ((Integer) CommAndData[1][i]).intValue();
                 } else if (Color.class.isInstance(CommAndData[1][i])) {
                     curColor = (Color) CommAndData[1][i];
                 }
                 break;
             }
        }
    }    private void drawAction(Graphics g, Color color, int type, Point sP, Point eP) {
        g.setColor(color);
        switch (type) {
            case line :
                g.drawLine(sP.x, sP.y, eP.x, eP.y);
                break;
            case circle :
                drawCircle(sP, eP, g);
                break;
        }
    }    public static Point getCenterPoint(Point p1, Point p2) {
        int x = p1.x + (p2.x - p1.x) / 2;
        int y = p1.y + (p2.y - p1.y) / 2;        return new Point(x, y);
    }

Answer 1

public static int getTwoPointsLength(Point p1, Point p2) {
        return (int) Math.sqrt((p2.x - p1.x) * (p2.x - p1.x) + (p2.y - p1.y) * (p2.y - p1.y));
    }    public static void drawCircle(Point startPoint, Point endPoint, Graphics g) {
        int diameter = getTwoPointsLength(startPoint, endPoint);
        int radius = diameter/2;
        Point centerPoint = getCenterPoint(startPoint, endPoint);
        Point reviseStartPoint =
            new Point(centerPoint.x - radius, centerPoint.y - radius);        g.drawOval(reviseStartPoint.x, reviseStartPoint.y, diameter, diameter);
    }    private void refresh(Graphics g) {
        if (g == null) return;
        java.util.Iterator ite = actionBuf.iterator();
        ActionProperty p;        while (ite.hasNext()) {
            p = (ActionProperty) ite.next();
            drawAction(g, p.getColor(), p.getType(), p.getStartPoint(), p.getEndPoint());
        }
    }    class MyMouseListener extends MouseAdapter {
        public void mousePressed(MouseEvent e) {        }        public void mouseReleased(MouseEvent e) {
            flag = true;
            actionBuf.add(new ActionProperty(
                new Color(curColor.getRGB()),
                curType, new Point(startPoint), new Point(endPoint)));//            java.util.Iterator ite = vector.iterator();
//            ActionProperty p;
//            int maxX = 0, maxY = 0;
//            while (ite.hasNext()) {
//                p = (ActionProperty) ite.next();
//                if (p.getStartPoint().x > maxX) {
//                    maxX = p.getStartPoint().x;
//                }
//                if (p.getEndPoint().x > maxX) {
//                    maxX = p.getEndPoint().x;
//                }
//                if (p.getStartPoint().y > maxY) {
//                    maxY = p.getStartPoint().y;
//                }
//                if (p.getEndPoint().y > maxY) {
//                    maxY = p.getEndPoint().y;
//                }
//            }
//            shapeCanvas.setPreferredSize(new Dimension(maxX, maxY));
        }        public void mouseEntered(MouseEvent e) {
            shapePanel.setCursor(new Cursor(Cursor.CROSSHAIR_CURSOR));
        }        public void mouseExited(MouseEvent e) {        }
    }    class MyMouseMotion extends MouseMotionAdapter {
        public void mouseDragged(MouseEvent e) {
            if (flag) {
                startPoint = e.getPoint();
                endPoint = e.getPoint();
                flag = false;
                (new Monitor()).start();
            }
            if (g == null) {
                g = shapePanel.getGraphics();
            }
            drawAction(g, shapePanel.getBackground(), curType, startPoint, endPoint);
            refresh(g);
            g.setColor(curColor);
            endPoint = e.getPoint();
            drawAction(g, curColor, curType, startPoint, endPoint);
        }
    }    private class ActionProperty {
        private Color color;
        private int type;
        private Point sP, eP;        ActionProperty(){};
        ActionProperty(Color color, int type, Point startPoint, Point endPoint) {
            this.color = color;
            this.type = type;
            this.sP = startPoint;
            this.eP = endPoint;
        }        void setColor(Color color) {
            this.color = color;
        }        void setType(int type) {
            this.type = type;
        }        void setStartPoint(Point startPoint) {
            this.sP = startPoint;
        }        void setEndPoint(Point endPoint) {
            this.eP = endPoint;
        }        Color getColor() {
            return this.color;
        }        int getType() {
            return this.type;
        }        Point getStartPoint() {
            return this.sP;
        }        Point getEndPoint() {
            return this.eP;
        }
    }    private class ShapePanel extends JPanel {
    }    private class Monitor extends Thread {
        public synchronized void run() {
            while (true) {
                refresh(g);
                try {
                    wait(50);
                } catch (InterruptedException ex) {}
            }
        }
    }
    public static void main(String[] args) {
        new DrawShape();
//        System.out.println(getTwoPointsLength(new Point(1, 1), new Point(4, 5)));
    }
}