下面的代码有几个问题：
1）多边形连接最后一个点和第一个点本身，不应该自己做，但用户应该绘制它。
2）单击其他形状后，多边形线消失了。
package Circles;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Path2D;
import javax.swing.*;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.Iterator;
//////////////////////////////////////////////////////////////PaintDemo
class PaintDemo2 {
//============================================================= main
public static void main(String[] args) {
PaintWindow2 window = new PaintWindow2();
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setVisible(true);
}//end main
}//endclass PaintDemo
@SuppressWarnings("serial")
////////////////////////////////////////////////////////////PaintWindow
class PaintWindow2 extends JFrame {
PaintPanel2 canvas = new PaintPanel2();
//====================================================== constructor
public PaintWindow2() {
//--- create the buttons
JButton circleButton = new JButton("Circle");
circleButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
canvas.setShape(PaintPanel2.CIRCLE);
}});
JButton rectangleButton = new JButton("Rectangle");
rectangleButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
canvas.setShape(PaintPanel2.Ellipse);
}});
JButton polyButton = new JButton("Polygon");
polyButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
canvas.setShape(PaintPanel2.POLY);
}});
//--- layout the buttons
JPanel buttonPanel = new JPanel();
buttonPanel.setLayout(new GridLayout(2, 1));
buttonPanel.add(circleButton);
buttonPanel.add(rectangleButton);
buttonPanel.add(polyButton);
//--- layout the window
Container content = this.getContentPane();
content.setLayout(new BorderLayout());
content.add(buttonPanel, BorderLayout.WEST);
content.add(canvas , BorderLayout.CENTER);
this.setTitle("Paint Demo");
this.pack();
}//end constructor
}//endclass PaintWindow
///////////////////////////////////////////////////////////// PaintPanel2
@SuppressWarnings("serial")
class PaintPanel2 extends JPanel implements MouseListener,
MouseMotionListener {
//--- Public constants used to specify shape being drawn.
public static final int NONE = 0;
public static final int LINE = 1;
public static final int Ellipse = 2;
public static final int CIRCLE = 3;
public static final int POLY = 4;
//--- Variables to store the current figure info
private int _shape = NONE;
public int getShape() {
return _shape;
}
private int _currentStartX = 0; // where mouse first pressed
private int _currentStartY = 0;
private int _currentEndX = 0; // where dragged to or released
private int _currentEndY = 0;
//--- BufferedImage to store the underlying saved painting.
// Will be initialized first time paintComponent is called.
private BufferedImage _bufImage = null;
private boolean polygonIsNowComplete = false;
//--- Private constant for size of paint area.
private static final int SIZE = 600; // size of paint area
private final Point trackPoint = new Point();
private Path2D currentShape;
private ArrayList<Path2D> lstPloys = new ArrayList<Path2D>();;
private Point lastPoint;
private Point currentPoint;
@SuppressWarnings("rawtypes")
private ArrayList points = new ArrayList();
//====================================================== constructor
public PaintPanel2() {
setPreferredSize(new Dimension(SIZE, SIZE));
setBackground(Color.white);
//--- Add the mouse listeners.
this.addMouseListener(this);
this.addMouseMotionListener(this);
}//endconstructor
//========================================================= setShape
public void setShape(int shape) {
//--- Provided so users can set the shape.
_shape = shape;
}//end setShape
//=================================================== paintComponent
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g; // downcast to Graphics2D
if (_bufImage == null) {
//--- This is the first time, initialize _bufImage
int w = this.getWidth();
int h = this.getHeight();
_bufImage = (BufferedImage)this.createImage(w, h);
Graphics2D gc = _bufImage.createGraphics();
gc.setColor(Color.white);
gc.fillRect(0, 0, w, h); // fill in background
}
g2.drawImage(_bufImage, null, 0, 0); // draw previous shapes
drawCurrentShape(g2);
}//end paintComponent
//================================================= drawCurrentShape
private void drawCurrentShape(Graphics2D g2) {
//--- Draws current shape on a graphics context, either
// on the context passed to paintComponent, or the
// context for the BufferedImage.
switch (_shape) {
case NONE :
break;
case CIRCLE:
g2.drawOval(_currentStartX, _currentStartY,
_currentEndX - _currentStartX,
_currentEndY - _currentStartY);
break;
case Ellipse:
g2.draw(new Ellipse2D.Double(_currentStartX, _currentStartY,
_currentEndX - _currentStartX,
_currentEndY - _currentStartY));
break;
case POLY:
drawPolyGon(g2);
break;
default: // should never happen
g2.drawString("Huh?", 10, 20);
break;
}
}//end paintComponent
private void drawPolyGon(Graphics2D g2) {
g2.create();
if (lastPoint != null) {
g2.setColor(Color.RED);
g2.fillOval(lastPoint.x - 2, lastPoint.y - 2, 4, 4);
}
if (currentShape != null) {
g2.setColor(Color.RED);
g2.draw(currentShape);
if (lastPoint != null && currentPoint != null) {
g2.setColor(new Color(255, 0, 0, 64));
g2.draw(new Line2D.Float(lastPoint, currentPoint));
}
}
g2.setColor(Color.BLACK);
for (Path2D shape : lstPloys) {
g2.draw(shape);
}
g2.dispose();
// TODO Auto-generated method stub
}
//===================================================== mousePressed
public void mousePressed(MouseEvent e) {
_currentStartX = e.getX(); // save x coordinate of the click
_currentStartY = e.getY(); // save y
_currentEndX = _currentStartX; // set end to same pixel
_currentEndY = _currentStartY;
}//end mousePressed
//===================================================== mouseDragged
public void mouseDragged(MouseEvent e) {
_currentEndX = e.getX(); // save new x and y coordinates
_currentEndY = e.getY();
this.repaint();
// show new shape
}//end mouseDragged
//==================================================== mouseReleased
public void mouseReleased(MouseEvent e) {
// This will save the shape that has been dragged by
// drawing it onto the bufferedImage where all shapes
// are written.
_currentEndX = e.getX(); // save ending coordinates
_currentEndY = e.getY();
//--- Draw the current shape onto the buffered image.
Graphics2D grafarea = _bufImage.createGraphics();
drawCurrentShape(grafarea);
this.repaint();
}//end mouseReleased
public void mouseMoved (MouseEvent e) {
if (currentShape != null) {
currentPoint = e.getPoint();
repaint();
} else {
currentPoint = null;
}
}
public void mouseEntered (MouseEvent e) {}
public void mouseExited (MouseEvent e) {}
public void mouseClicked (MouseEvent e) {
if (e.getButton() == MouseEvent.BUTTON1) {
if (e.getClickCount() == 1) {
Point p = e.getPoint();
lastPoint = p;
if (currentShape == null) {
currentShape = new Path2D.Float();
currentShape.moveTo(p.x, p.y);
} else {
currentShape.lineTo(p.x, p.y);
}
repaint();
} else if (e.getClickCount() == 2) {
currentShape.closePath();
lstPloys.add(currentShape);
currentShape = null;
lastPoint = null;
repaint();
}
}
}
}