Question

JAVA画图板的问题

要用applet实现一个简单的画图板 可以画圆，四边形，圆形，我写了一个程序 但是每次点按钮的时候都会有一大堆错误 求高手帮忙看一下应该怎么写
public class painting extends JApplet{
private JRadioButton lineButton;
private JRadioButton rectangleButton;
private JRadioButton circleButton;
private int currentX = 0;
private int currentY = 0;
private int width = 0;
private int height = 0;
public Graphics g2;

public void init(){
setSize(700,500);
JPanel panel = buildPanel();
add(panel);

addMouseListener(new MyMouseListener());
addMouseMotionListener(new MyMouseMotionListener());
}

private JPanel buildPanel(){
lineButton = new JRadioButton("line");
rectangleButton = new JRadioButton("rectangel");
circleButton = new JRadioButton("circle");

ButtonGroup group = new ButtonGroup();
group.add(lineButton);
group.add(rectangleButton);
group.add(circleButton);

MyListener listener = new MyListener();
lineButton.addActionListener(listener);
rectangleButton.addActionListener(listener);
circleButton.addActionListener(listener);

JPanel panel = new JPanel();
panel.add(lineButton);
panel.add(rectangleButton);
panel.add(circleButton);
return panel;

}
public void paintComponent(Graphics g){
super.paintComponents(g);
g2=(Graphics2D)g;
}

private class MyListener implements ActionListener{
public void actionPerformed(ActionEvent e){
if (lineButton.isSelected()){
Line2D line = new Line2D.Double();
line.setLine(currentX, currentY, width, height);
((Graphics2D) g2).draw(line);
}
else if (rectangleButton.isSelected()){
Rectangle2D rectangle = new Rectangle2D.Double();
rectangle.setRect(currentX, currentY, width, height);
((Graphics2D) g2).draw(rectangle);
}
else if (circleButton.isSelected()){
Ellipse2D circle=new Ellipse2D.Double();
circle.setFrame(currentX, currentY, width, height);
((Graphics2D) g2).draw(circle);
}
}

}

private class MyMouseListener extends MouseAdapter{
public void mousePressed(MouseEvent e){
currentX = e.getX();
currentY = e.getY();
} }
}
private class MyMouseMotionListener extends MouseMotionAdapter{
public void mouseDragged(MouseEvent e){
width = e.getX() - currentX;
height = e.getY() - currentY;

// Repaint the window.
repaint();

Answer 1

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

public class painting extends JApplet{
private JRadioButton lineButton;
private JRadioButton rectangleButton;
private JRadioButton circleButton;

PaintPanel paintPanel;
JPanel panel;

private int shape = 0;//这里是我加上去的如果shape==1,就画线,为2就画圆矩形,为3为来圆形
boolean isFirst = true;

public void init(){
//setSize(700,500);
lineButton = new JRadioButton("line");
rectangleButton = new JRadioButton("rectangel");
circleButton = new JRadioButton("circle");

ButtonGroup group = new ButtonGroup();
group.add(lineButton);
group.add(rectangleButton);
group.add(circleButton);

MyListener listener = new MyListener();
lineButton.addActionListener(listener);
rectangleButton.addActionListener(listener);
circleButton.addActionListener(listener);

panel = new JPanel();
panel.add(lineButton);
panel.add(rectangleButton);
panel.add(circleButton);

paintPanel = new PaintPanel();
paintPanel.setBackground(Color.blue);
add(panel,BorderLayout.NORTH);
add(paintPanel,BorderLayout.CENTER);

paintPanel.addMouseListener(
new MouseAdapter(){
public void mousePressed(MouseEvent e){
if(isFirst){
paintPanel.setCurrentXY(e.getX(), e.getY());
isFirst = false;
}
else{
paintPanel.setLastXY(e.getX(),e.getY());
paintPanel.repaint();
isFirst = true;
}
}

public void mouseReleased(MouseEvent e){

}
});
paintPanel.addMouseMotionListener(
new MouseMotionAdapter(){
public void mouseDragged(MouseEvent e){

paintPanel.setLastXY(e.getX(),e.getY());
isFirst = true;

// Repaint the window.
paintPanel.repaint();
}
});
}

private class MyListener implements ActionListener{
public void actionPerformed(ActionEvent e){
if (e.getSource() == lineButton){
shape = 1;
//paintPanel.repaint();
}
else if (e.getSource()==rectangleButton){
shape = 2;
//paintPanel.repaint();
}
else if (e.getSource()==circleButton){
shape = 3;
//paintPanel.repaint();
}
}

}

public class PaintPanel extends JPanel{
private int currentX = 100;
private int currentY = 100;
private int lastX = 100;
private int lastY = 100;
//public Graphics g2;
public void paintComponent(Graphics g){

super.paintComponents(g);
Graphics2D g2=(Graphics2D)g; //这里要先声明类型，因为在头部我已经把//public Graphics g2; 删了。wich
switch(shape){//判断要画什么图
case 1 :g2.draw(new Line2D.Double(currentX, currentY, lastX, lastY));break;
case 2 :g2.draw(new Rectangle2D.Double(currentX, currentY,
Math.abs(currentX-lastX), Math.abs(currentY-lastY)));break;
case 3 :g2.draw(new Ellipse2D.Double(currentX, currentY,
Math.abs(currentX-lastX), Math.abs(currentY-lastY)));break;

}
}

public void setCurrentXY(int x,int y){
currentX = x;
currentY = y;
}

public void setLastXY(int w,int h ){
lastX = w;
lastY = h;
}

public int getX(){
return currentX;

}

public int getY(){
return currentY;
}
}

}