JAVA画图板程序，用netbeans做，要求画圆，椭圆，直线，三角形，矩形，可以填充颜色和擦除

import java.applet.*; 
import java.awt.*; 
import java.awt.event.*; 
import java.util.*; 
import javax.swing.*; 
import java.awt.geom.*; 
import java.io.*; 
import java.sql.Connection;

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() 
{ 
            @Override
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; ip1 = (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(); 
            switch (name) {
                case "black":
                    c = new Color(0,0,0);
                    break;
                case "red":
                    c = new Color(255,0,0);
                    break;
                case "green":
                    c = new Color(0,255,0);
                    break;
                case "blue":
                    c = new Color(0,0,255);
                    break;
            }
} 
else if(e.getSource()==SizeChoice)//画笔大小 
{ 
String selected = SizeChoice.getSelectedItem(); 
            switch (selected) {
                case "1":
                    con = 1;
                    size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
                    break;
                case "3":
                    con = 3;
                    size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
                    break;
                case "5":
                    con = 5;
                    size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
                    break;
                case "7":
                    con = 7;
                    size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
                    break;
                case "9":
                    con = 9;
                    size = new BasicStroke(con,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
                    break;
            }
} 
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"); } 
}

楼上的代码我做了一点点改正，我想现在可以正常运行了：
//#8.15
//#filename: ShapeMain.java
import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionAdapter;
import java.awt.event.MouseMotionListener;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
//import javax.swing.Component;

public class ShapeMain extends JFrame implements ActionListener,MouseListener,MouseMotionListener{
int x,y,x1,y1,x2,y2,width,height;
boolean isFirstPoint = true;
//初始化开始画的是线
int drawType = PaintingGround.LINE;
//初始化开始不是填充
boolean isFill = false;
//添加控件
ButtonGroup btg = new ButtonGroup();
Button btLine = new Button("线");
Button btRectangle = new Button("矩形");
Button btRound = new Button("圆");
Button btEllipse = new Button("椭圆");
Button tbFillState = new Button("填充");
Button button3 = new Button("文本操作");
Button button2 = new Button("清除");
Button button1 = new Button("选择颜色");

Panel buttonPanel = new Panel();
PaintingGround paintingGround = new PaintingGround();
//Main Method
public static void main(String[] args) {
//设置显示外观
try{
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}catch(Exception e) {
e.printStackTrace();
}
new ShapeMain();
}

//构造函数
public ShapeMain() {
//控件添加到控件组中
// btg.add(btLine);
// btg.add(btRectangle);
// btg.add(btRound);
// btg.add(btEllipse);

buttonPanel.add(btLine);
buttonPanel.add(btRectangle);
buttonPanel.add(btRound);
buttonPanel.add(btEllipse);
buttonPanel.add(tbFillState);

//设置容器及容器的整体布局
Container cp = this;

cp.setLayout(new BorderLayout());

cp.add(BorderLayout.NORTH,buttonPanel);
cp.add(BorderLayout.CENTER,paintingGround);
//cp.add(BorderLayout.SOUTH,jf);
//jf.setJMenuBar(mb);
setLocation(300,150);
setSize(600,480);
setVisible(true);

setDefaultCloseOperation(EXIT_ON_CLOSE);
//添加鼠标触发事件
paintingGround.addMouseListener(new MouseAdapter() {
public void mouseReleased(MouseEvent evn) {
isFirstPoint = true;
}
});
//对鼠标的输入进行判断并调用画图程序
paintingGround.addMouseMotionListener(new MouseMotionAdapter() {
public void mouseDragged(MouseEvent evn) {
if(isFirstPoint) {
x1 = evn.getX();
y1 = evn.getY();
isFirstPoint = false;
}
else {
x2 = evn.getX();
y2 = evn.getY();
switch(drawType) {
case PaintingGround.LINE:
//画线
paintingGround.drawLine(x1,y1,x2,y2);
break;
case PaintingGround.RECTANGLE:
//画矫形
paintingGround.drawRect(x1,y1,x2-x1,y2-y1);
break;
case PaintingGround.ROUND:
//画圆
//两点距离公式
int size = Math.abs((int)Math.sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1)));
paintingGround.drawRound(x1,y1,size);
break;
case PaintingGround.ELLIPSE:
//画椭圆
paintingGround.drawEllipse(x1,y1,x2-x1,y2-y1);
break;
default:
break;
}
}
}
});
//各个控件的触发事件
btLine.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.LINE;
}
});

btRectangle.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.RECTANGLE;
}
});

btRound.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.ROUND;
}
});

btEllipse.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.ELLIPSE;
}
});

tbFillState.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
isFill = tbFillState.isShowing();
paintingGround.setFillState(isFill);
}
});
}

public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub

}

public void mouseClicked(MouseEvent e) {
// TODO Auto-generated method stub

}

public void mousePressed(MouseEvent e) {
// TODO Auto-generated method stub

}

public void mouseReleased(MouseEvent e) {
// TODO Auto-generated method stub

}

public void mouseEntered(MouseEvent e) {
// TODO Auto-generated method stub

}

public void mouseExited(MouseEvent e) {
// TODO Auto-generated method stub

}

public void mouseDragged(MouseEvent e) {
// TODO Auto-generated method stub

}

public void mouseMoved(MouseEvent e) {
// TODO Auto-generated method stub

}
}

class PaintingGround extends JPanel {
public static final int LINE = 1;
public static final int RECTANGLE = 2;
public static final int ROUND = 3;
public static final int ELLIPSE = 4;

private int x,y;
private int x1,y1,x2,y2;
private int width, height,size;
private int drawType = 0;
private boolean isFill = false;
//构造函数
public PaintingGround() {
setBackground(Color.black);
}
//判断是用实心还是空心的,
public void paint(Graphics g) {
super.paint(g);
g.setColor(Color.white);
if(isFill) {
switch(drawType) {
case LINE:
g.drawLine(x1,y1,x2,y2);
break;
case RECTANGLE:
g.fillRect(x,y,width,height);
break;
case ROUND:
g.fillOval(x,y,size,size);
break;
case ELLIPSE:
g.fillOval(x,y,width,height);
break;
default:
break;
}
}
else {
switch(drawType) {
case LINE:
g.drawLine(x1,y1,x2,y2);
break;
case RECTANGLE:
g.drawRect(x,y,width,height);
break;
case ROUND:
g.drawOval(x,y,size,size);
break;
case ELLIPSE:
g.drawOval(x,y,width,height);
break;
default:
break;
}
}
}

public void drawLine(int x1, int y1, int x2,int y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;

drawType = LINE;
repaint();
}
//具体的实现方式
public void drawRect(int x,int y,int width, int height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
drawType = RECTANGLE;
repaint();
}

public void drawRound(int x,int y,int size) {
this.x = x;
this.y = y;
this.size = size;
drawType = ROUND;
repaint();
}

public void drawEllipse(int x,int y,int width,int height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
drawType = ELLIPSE;
repaint();
}

public void setFillState(boolean isFill) {
this.isFill = isFill;
}

}