04年接触了一段时间的JAVA，期间写了比较多小程序段，写得最完整的就是这个JAVA小画板程序，涉及到鼠标事件、画图函数、文件流、文件的打开与保存等内容。 //powered by compower
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import java.awt.geom.*;
import java.io.*; class Point implements Serializable
{
int x,y;
Color col;
int tool;
int boarder; Point(int x, int y, Color col, int tool, int boarder)
{
this.x = x;
this.y = y;
this.col = col;
this.tool = tool;
this.boarder = boarder;
}
}
class paintboard extends Frame implements ActionListener,MouseMotionListener,MouseListener,ItemListener
{
int x = -1, y = -1;
int con = 1;//画笔大小
int Econ = 5;//橡皮大小
int toolFlag = 0;//toolFlag:工具标记
//toolFlag工具对应表：
//（0--画笔）；（1--橡皮）；（2--清除）；
//（3--直线）；（4--圆）；（5--矩形）； Color c = new Color(0,0,0); //画笔颜色
BasicStroke size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);//画笔粗细
Point cutflag = new Point(-1, -1, c, 6, con);//截断标志 Vector paintInfo = null;//点信息向量组
int n = 1; FileInputStream picIn = null;
FileOutputStream picOut = null;
ObjectInputStream VIn = null;
ObjectOutputStream VOut = null;
// *工具面板--画笔，直线，圆，矩形，多边形,橡皮，清除*/
Panel toolPanel;
Button eraser, drLine,drCircle,drRect;
Button clear ,pen;
Choice ColChoice,SizeChoice,EraserChoice;
Button colchooser;
Label 颜色,大小B,大小E;
//保存功能
Button openPic,savePic;
FileDialog openPicture,savePicture;
paintboard(String s)
{
super(s);
addMouseMotionListener(this);
addMouseListener(this); paintInfo = new Vector(); /*各工具按钮及选择项*/
//颜色选择
ColChoice = new Choice();
ColChoice.add("black");
ColChoice.add("red");
ColChoice.add("blue");
ColChoice.add("green");
ColChoice.addItemListener(this);
//画笔大小选择
SizeChoice = new Choice();
SizeChoice.add("1");
SizeChoice.add("3");
SizeChoice.add("5");
SizeChoice.add("7");
SizeChoice.add("9");
SizeChoice.addItemListener(this);
//橡皮大小选择
EraserChoice = new Choice();
EraserChoice.add("5");
EraserChoice.add("9");
EraserChoice.add("13");
EraserChoice.add("17");
EraserChoice.addItemListener(this);
////////////////////////////////////////////////////
toolPanel = new Panel(); clear = new Button("清除");
eraser = new Button("橡皮");
pen = new Button("画笔");
drLine = new Button("画直线");
drCircle = new Button("画圆形");
drRect = new Button("画矩形"); openPic = new Button("打开图画");
savePic = new Button("保存图画");
colchooser = new Button("显示调色板"); //各组件事件监听
clear.addActionListener(this);
eraser.addActionListener(this);
pen.addActionListener(this);
drLine.addActionListener(this);
drCircle.addActionListener(this);
drRect.addActionListener(this);
openPic.addActionListener(this);
savePic.addActionListener(this);
colchooser.addActionListener(this);
颜色 = new Label("画笔颜色",Label.CENTER);
大小B = new Label("画笔大小",Label.CENTER);
大小E = new Label("橡皮大小",Label.CENTER);
//面板添加组件
toolPanel.add(openPic);
toolPanel.add(savePic);
toolPanel.add(pen);
toolPanel.add(drLine);
toolPanel.add(drCircle);
toolPanel.add(drRect); toolPanel.add(颜色); toolPanel.add(ColChoice);
toolPanel.add(大小B); toolPanel.add(SizeChoice);
toolPanel.add(colchooser); toolPanel.add(eraser);
toolPanel.add(大小E); toolPanel.add(EraserChoice);
toolPanel.add(clear);
//工具面板到APPLET面板
add(toolPanel,BorderLayout.NORTH);
setBounds(60,60,900,600); setVisible(true);
validate();
//dialog for save and load openPicture = new FileDialog(this,"打开图画",FileDialog.LOAD);
openPicture.setVisible(false);
savePicture = new FileDialog(this,"保存图画",FileDialog.SAVE);
savePicture.setVisible(false); openPicture.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{ openPicture.setVisible(false); }
}); savePicture.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{ savePicture.setVisible(false); }
}); addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{ System.exit(0);}
});
} public void paint(Graphics g)
{
Graphics2D g2d = (Graphics2D)g; Point p1,p2; n = paintInfo.size();
if(toolFlag==2)
g.clearRect(0,0,getSize().width,getSize().height);//清除 for(int i=0; i<n-1; i++)
{
p1 = (Point)paintInfo.elementAt(i);
p2 = (Point)paintInfo.elementAt(i+1);
size = new BasicStroke(p1.boarder,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
g2d.setColor(p1.col);
g2d.setStroke(size);
if(p1.tool==p2.tool)
{
switch(p1.tool)
{
case 0://画笔 Line2D line1 = new Line2D.Double(p1.x, p1.y, p2.x, p2.y);
g2d.draw(line1);
break; case 1://橡皮
g.clearRect(p1.x, p1.y, p1.boarder, p1.boarder);
break; case 3://画直线
Line2D line2 = new Line2D.Double(p1.x, p1.y, p2.x, p2.y);
g2d.draw(line2);
break; case 4://画圆
Ellipse2D ellipse = new Ellipse2D.Double(p1.x, p1.y, Math.abs(p2.x-p1.x) , Math.abs(p2.y-p1.y));
g2d.draw(ellipse);
break; case 5://画矩形
Rectangle2D rect = new Rectangle2D.Double(p1.x, p1.y, Math.abs(p2.x-p1.x) , Math.abs(p2.y-p1.y));
g2d.draw(rect);
break; case 6://截断，跳过
i=i+1;
break; default :
}//end switch
}//end if
}//end for
}
public void itemStateChanged(ItemEvent e)
{
if(e.getSource()==ColChoice)//预选颜色
{
String name = ColChoice.getSelectedItem();
if(name=="black")
{ c = new Color(0,0,0); }
else if(name=="red")
{ c = new Color(255,0,0); }
else if(name=="green")
{ c = new Color(0,255,0); }
else if(name=="blue")
{ c = new Color(0,0,255); }
}
else if(e.getSource()==SizeChoice)//画笔大小
{
String selected = SizeChoice.getSelectedItem();
if(selected=="1")
{
con = 1;
size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
}
else if(selected=="3")
{
con = 3;
size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL); }
else if(selected=="5")
{ con = 5;
size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL); }
else if(selected=="7")
{ con = 7;
size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL); }
else if(selected=="9")
{ con = 9;
size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL); }
}
else if(e.getSource()==EraserChoice)//橡皮大小
{
String Esize = EraserChoice.getSelectedItem(); if(Esize=="5")
{ Econ = 5*2; }
else if(Esize=="9")
{ Econ = 9*2; }
else if(Esize=="13")
{ Econ = 13*2; }
else if(Esize=="17")
{ Econ = 17*3; } } } public void mouseDragged(MouseEvent e)
{
Point p1 ;
switch(toolFlag){
case 0://画笔
x = (int)e.getX();
y = (int)e.getY();
p1 = new Point(x, y, c, toolFlag, con);
paintInfo.addElement(p1);
repaint();
break; case 1://橡皮
x = (int)e.getX();
y = (int)e.getY();
p1 = new Point(x, y, null, toolFlag, Econ);
paintInfo.addElement(p1);
repaint();
break; default :
}
} public void mouseMoved(MouseEvent e) {} public void update(Graphics g)
{
paint(g);
} public void mousePressed(MouseEvent e)
{
Point p2;
switch(toolFlag){
case 3://直线
x = (int)e.getX();
y = (int)e.getY();
p2 = new Point(x, y, c, toolFlag, con);
paintInfo.addElement(p2);
break; case 4: //圆
x = (int)e.getX();
y = (int)e.getY();
p2 = new Point(x, y, c, toolFlag, con);
paintInfo.addElement(p2);
break; case 5: //矩形
x = (int)e.getX();
y = (int)e.getY();
p2 = new Point(x, y, c, toolFlag, con);
paintInfo.addElement(p2);
break; default :
}
} public void mouseReleased(MouseEvent e)
{
Point p3;
switch(toolFlag){
case 0: //画笔
paintInfo.addElement(cutflag);
break; case 1: //eraser
paintInfo.addElement(cutflag);
break; case 3: //直线
x = (int)e.getX();
y = (int)e.getY();
p3 = new Point(x, y, c, toolFlag, con);
paintInfo.addElement(p3);
paintInfo.addElement(cutflag);
repaint();
break; case 4: //圆
x = (int)e.getX();
y = (int)e.getY();
p3 = new Point(x, y, c, toolFlag, con);
paintInfo.addElement(p3);
paintInfo.addElement(cutflag);
repaint();
break; case 5: //矩形
x = (int)e.getX();
y = (int)e.getY();
p3 = new Point(x, y, c, toolFlag, con);
paintInfo.addElement(p3);
paintInfo.addElement(cutflag);
repaint();
break; default:
}
} public void mouseEntered(MouseEvent e){} public void mouseExited(MouseEvent e){} public void mouseClicked(MouseEvent e){} public void actionPerformed(ActionEvent e)
{
if(e.getSource()==pen)//画笔
{ toolFlag = 0; } if(e.getSource()==eraser)//橡皮
{ toolFlag = 1; }
if(e.getSource()==clear)//清除
{
toolFlag = 2;
paintInfo.removeAllElements();
repaint();
}
if(e.getSource()==drLine)//画线
{ toolFlag = 3; } if(e.getSource()==drCircle)//画圆
{ toolFlag = 4; } if(e.getSource()==drRect)//画矩形
{ toolFlag = 5; } if(e.getSource()==colchooser)//调色板
{
Color newColor = JColorChooser.showDialog(this,"调色板",c);
c = newColor;
} if(e.getSource()==openPic)//打开图画
{
openPicture.setVisible(true);
if(openPicture.getFile()!=null)
{
int tempflag;
tempflag = toolFlag;
toolFlag = 2 ;
repaint(); try{
paintInfo.removeAllElements();
File filein = new File(openPicture.getDirectory(),openPicture.getFile());
picIn = new FileInputStream(filein);
VIn = new ObjectInputStream(picIn);
paintInfo = (Vector)VIn.readObject();
VIn.close();
repaint();
toolFlag = tempflag; } catch(ClassNotFoundException IOe2)
{
repaint();
toolFlag = tempflag;
System.out.println("can not read object");
}
catch(IOException IOe)
{
repaint();
toolFlag = tempflag;
System.out.println("can not read file");
}
} } if(e.getSource()==savePic)//保存图画
{
savePicture.setVisible(true);
try{
File fileout = new File(savePicture.getDirectory(),savePicture.getFile());
picOut = new FileOutputStream(fileout);
VOut = new ObjectOutputStream(picOut);
VOut.writeObject(paintInfo);
VOut.close();
}
catch(IOException IOe)
{
System.out.println("can not write object");
}
}
}
}//end paintboard public class pb
{
public static void main(String args[])
{ new paintboard("画图程序"); }
} 
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