HandDraw2.java

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
public class HandDraw2
{
	//画图区的宽度
	private final int AREA_WIDTH = 500;
	//画图区的长度
	private final int AREA_HEIGHT = 400;
	//下面的preX 、preY保存上一次鼠标拖动事件的鼠标坐标
	private int preX = -1;
	private int preY = -1;
	//顶一个一个右键菜单用于设置画笔颜色
	JPopupMenu pop = new JPopupMenu();
	JMenuItem chooseColor = new JMenuItem("选择颜色");
	//定义一个BufferedImage
	BufferedImage image = new BufferedImage(AREA_WIDTH , AREA_HEIGHT , 
		BufferedImage.TYPE_INT_RGB);
	//获取image的Graphics
	Graphics g = image.getGraphics();
	private JFrame f = new JFrame("简单手绘程序");
	private DrawCanvas drawArea = new DrawCanvas();
	//用于保存需要绘制什么图形的字符串属性
	private String shape = "";
	//用于保存画笔颜色
	private Color foreColor = new Color(255, 0 ,0);
	public void init()
	{
		chooseColor.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent ae)
			{
				//下面代码直接弹出一个模式的颜色选择器对话框，并返回用户选择的颜色
				//foreColor = JColorChooser.showDialog(f , "Ñ¡Ôñ»­±ÊÑÕÉ«" , foreColor);
				//下面代码可以弹出一个非模式的颜色选择对话框
				//并可以分别为“确定”按钮、“取消”按钮指定事件监听器
				final JColorChooser colorPane = new JColorChooser(foreColor);
				JDialog jd = JColorChooser.createDialog(f ,"选择画笔颜色",false, 
					colorPane, new ActionListener()
					{
						public void actionPerformed(ActionEvent ae)
						{
							foreColor = colorPane.getColor();
						}
					}, null);
				jd.setVisible(true);
			}
		});
		//将菜单项组合成右键菜单
		pop.add(chooseColor);
		//将右键菜单添加到drawArea对象中
		drawArea.setComponentPopupMenu(pop);
		//将image对象的背景色填充成白色
		g.fillRect(0 , 0 ,AREA_WIDTH , AREA_HEIGHT);
		drawArea.setPreferredSize(new Dimension(AREA_WIDTH , AREA_HEIGHT));
		//监听鼠标移动动作
		drawArea.addMouseMotionListener(new MouseMotionAdapter()
		{
			//实现按下鼠标键并拖动的事件处理器
			public void mouseDragged(MouseEvent e)
			{
				if (preX > 0 && preY > 0)
				{
					//设置当前颜色
					g.setColor(foreColor);
					//绘制从上一次鼠标拖动事件点到本次鼠标事件点的线段
					g.drawLine(preX , preY , e.getX() , e.getY());
				}
				//将当前鼠标事件点的X、Y坐标保存起来
				preX = e.getX();
				preY = e.getY();
				//重绘drawArea对象
				drawArea.repaint();
			}
		});
		//监听鼠标事件
		drawArea.addMouseListener(new MouseAdapter()
		{
			//实现鼠标松开的事件处理器
			public void mouseReleased(MouseEvent e)
			{
				//松开鼠标键时，把上一次鼠标拖动事件的X、Y坐标为-1
				preX = -1;
				preY = -1;
			}
		});
		f.add(drawArea);
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.pack();
		f.setVisible(true);
	}
	public static void main(String[] args) 
	{
		new HandDraw2().init();
	}
	//让画图区域继承JPanel类
	class DrawCanvas extends JPanel
	{
		//重写JPanelde paint方法，实现绘画
		public void paint(Graphics g)
		{
			//将image绘制到该组件上
			g.drawImage(image , 0 , 0 , null);
		}
	}
}