paintpanel.java

一些JAVA的小程序

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

public class PaintPanel extends JPanel {
        public PaintPanel() {
                setLayout(new BorderLayout());
		JPanel p = new JPanel();
		p.setLayout(new GridLayout(1, 3));
		p.add(new Rectangle());
		p.add(new Oval());
		p.add(new Line());
		add(p, "North");
		MouseKeeper k = new MouseKeeper();
		addMouseListener(k);
		addMouseMotionListener(k);
	}

	private Image image = null;
	private Shape currentShape = null;

	private abstract class Shape extends JButton
						implements ActionListener {
		public Shape(String name) {
			super(name);
			addActionListener(this);
		}

		public abstract void draw(Graphics g, int a, int b, int c, int d);

		public void actionPerformed(ActionEvent e) {
			currentShape = this;
		}
	}

	private class Rectangle extends Shape {

		public Rectangle() {
			super("Rectangle");
		}

		public void draw(Graphics g, int a, int b, int c, int d) {
			int w = c - a;
			int h = d - b;
			g.drawRect(a, b, w, h);
		}
	}

	private class Oval extends Shape {

		public Oval() {
			super("Oval");
		}

		public void draw(Graphics g, int a, int b, int c, int d) {
			int w = c - a;
			int h = d - b;
			g.drawOval(a, b, w, h);
		}
	}

	private class Line extends Shape {

		public Line() {
			super("Line");
		}

		public void draw(Graphics g, int a, int b, int c, int d) {
			g.drawLine(a, b, c, d);
		}

	}

	private class MouseKeeper extends MouseAdapter
						implements MouseMotionListener {

		private int startx, starty;
		private int lastx, lasty;

		public void mousePressed(MouseEvent e) {
			lastx = startx = e.getX();
			lasty = starty = e.getY() - 50;
		}

		private void drawShape(Graphics g) {
			if (currentShape != null)
				currentShape.draw(g, startx, starty, lastx, lasty);
		}

		public void mouseDragged(MouseEvent e) {
			Graphics g = image.getGraphics();
			g.setXORMode(Color.white);
			drawShape(g);
			lastx = e.getX(); lasty = e.getY() - 50;
			drawShape(g);
			repaint();
		}

		public void mouseReleased(MouseEvent e) {
			Graphics g = image.getGraphics();
			g.setXORMode(Color.white);
			drawShape(g);
			g.setPaintMode();
			lastx = e.getX(); lasty = e.getY() - 50;
			drawShape(g);
			repaint();
		}

		public void mouseMoved(MouseEvent e) {}
	}


	public void paintComponent(Graphics g) {
		super.paintComponent(g);
		if(image == null)
			image = createImage(400,300);
		if (image!= null)
			g.drawImage(image, 0, 49, this);
	}
}