simpledrawboard.java

一个使用Java完成的简易绘图板

package simpledrawboard;

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

/**
* 简单的画图板
*/
class SimpleDrawBoard extends JFrame implements ActionListener {
    static int first = 0;
    int x1,y1,x2,y2,px,py,width,hight,flag;
    JRadioButton b1,b2,b3,b4,b5;
    JPanel bottom;
    ButtonGroup group;

    public SimpleDrawBoard() {
        super("Example of mouse event handling");

        setBounds(100,100,450,120);
        setSize(800,600);
        bottom=new JPanel();
        group=new ButtonGroup();
        b1 = new JRadioButton("自由绘图");
        b1.addActionListener(this);
        group.add(b1);
        bottom.add(b1);
        b2 = new JRadioButton("画直线");
        b2.addActionListener(this);
        group.add(b2);
        bottom.add(b2);
        b3 = new JRadioButton("画矩形");
        b3.addActionListener(this);
        group.add(b3);
        bottom.add(b3);
        b4 = new JRadioButton("画椭圆");
        b4.addActionListener(this);
        group.add(b4);
        bottom.add(b4);
        b5 = new JRadioButton("清空");
        b5.addActionListener(this);
        b5.setVisible(true);
        group.add(b5);
        bottom.add(b5);
        bottom.setVisible(true);
        bottom.repaint();
        add(bottom,BorderLayout.NORTH);

        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setResizable(false);

        addMouseListener(new MouseListener() {
            public void mouseClicked(MouseEvent e) {
            }
            public void mouseEntered(MouseEvent e) {
            }
            public void mouseExited(MouseEvent e) {
            }
            public void mousePressed(MouseEvent e) {
                if(flag==1||flag==2) {
                    x1 = e.getX();
                    y1 = e.getY();
                    x2 = x1;
                    y2 = y1;
                    repaint();
                } else if(flag==3||flag==4) {
                    x1 = e.getX();
                    y1 = e.getY();
                    px = x1;
                    py = y1;
                }
            }
            public void mouseReleased(MouseEvent e) {
                if(flag==2) {
                    x2 = x1;
                    y2 = y1;
                    x1 = e.getX();
                    y1 = e.getY();
                    repaint();
                } else if(flag==3||flag==4) {
                    x2 = e.getX();
                    y2 = e.getY();
                    if(x1 > x2 || y1 > y2) {
                        x1 = x1 + x2;
                        x2 = x1 - x2;
                        x1 = x1 - x2;
                        y1 = y1 + y2;
                        y2 = y1 - y2;
                        y1 = y1 - y2;
                        px = x1;
                        py = y1;
                    }
                    width = Math.abs(x2 - px);
                    hight = Math.abs(y2 - py);
                    repaint();
                }
            }
        });
        addMouseMotionListener(new MouseMotionListener() {
            public void mouseDragged(MouseEvent e) {
                if(flag == 1) {
                    x2 = x1;
                    y2 = y1;
                    x1 = e.getX();
                    y1 = e.getY();
                    repaint();
                }
            }
            public void mouseMoved(MouseEvent e) {
            }
        });
    }

    public void paint(Graphics g) {
        if(first == 0) {
            super.paint(g);
            first = 1;
        }
        g.setColor(Color.white);
        g.drawLine(0,65,800,65);
        g.setColor(Color.black);
        if(flag == 1 || flag == 2)
            g.drawLine(x1,y1,x2,y2);
        else if(flag == 3)
            g.drawRect(px,py,width,hight);
        else if(flag == 4)
            g.drawOval(px,py,width,hight);
    }

    public void actionPerformed(ActionEvent e) {
        try {
            Graphics g=getGraphics();
            if(e.getSource() == b1)
                flag = 1;
            else if(e.getSource() == b2)
                flag = 2;
            else if(e.getSource() == b3)
                flag = 3;
            else if(e.getSource() == b4)
                flag = 4;
            else if(e.getSource() == b5) {
                flag = 5;
                g.clearRect(0,66,800,534);
            }
        } catch(Exception event) {
        }
    }

    public static void main(String [] args) {
        JFrame f = new SimpleDrawBoard();
    }
}