Question

求Java画图版，能画正多边形的代码！

设计一个交互式程序，绘制图形包括园、三角形、正方形、五边形、六边形其中的一种，大小由鼠标拖动决定。题目说明：
选择一个容器Jframe
用public void actionPerformed(ActionEvent e){
……
}定义移动鼠标指针
用public void mouseDragged(MouseEvent e){
……
g2.setXORMode（Color.black）;
……
}定义拖动鼠标指针
public void mouseReleased(MouseEvent e){
……
}定义释放鼠标左键
重点在于如何绘制多边图形，在JAVA API中查找drawPolygon（）方法。
对于颜色的改变见颜色选择器JcolorChooser，按照这个的提示做，谢谢好心人了！

Answer 1

public class MiniDraw implements ActionListener, MouseListener{ // Fields private JFrame frame = new JFrame("MiniDraw");
private DrawingCanvas canvas = new DrawingCanvas(); private JButton colorButton; // the button for colour, so we can change its background to the current color.
private JTextField textField; // the field for entering text to put on the canvas // fields for recording the information needed to perform the next action
private enum Action {Line,Rect, Oval, Triangle, Text, Dot, Move, Delete, Push, Pull}; private int pressedX; //where the mouse was pressed
private int pressedY; //where the mouse was pressed
private Action currentAction = Action.Line;
private Color currentColor = Color.black; private List<Shape> shapes = new ArrayList <Shape>();

/** Constructor sets up the GUI. */
public MiniDraw(){
frame.setSize(800,600); //The graphics area
canvas.addMouseListener(this);
frame.getContentPane().add(canvas, BorderLayout.CENTER); //The buttons
JPanel topPanel = new JPanel( );
frame.getContentPane().add(topPanel, BorderLayout.NORTH);
JPanel botPanel = new JPanel( );
frame.getContentPane().add(botPanel, BorderLayout.SOUTH);
addButton(topPanel, "New");
addButton(topPanel, "Open");
addButton(topPanel, "Save");
addButton(topPanel, "Delete");
addButton(topPanel, "Move");
colorButton = addButton(topPanel, "Color"); // remember the button so we can change its colour
addButton(topPanel, "Push");
addButton(topPanel, "Pull");
addButton(topPanel, "Reverse");
addButton(topPanel, "Quit"); botPanel.add(new JLabel("Shapes: "));
addButton(botPanel, "Line");
addButton(botPanel, "Rect");
addButton(botPanel, "Oval");
addButton(botPanel, "Triangle");
addButton(botPanel, "Dot");
addButton(botPanel, "Text");
textField = new JTextField("Enter text", 12);
botPanel.add(new JLabel(" : "));
botPanel.add(textField); frame.setVisible(true);
} /** Utility method to make new button and add it to the panel
Returns the button, in case we need it. */
private JButton addButton(JPanel panel, String name){
JButton button = new JButton(name);
button.addActionListener(this);
panel.add(button);
return button;
} /** Respond to button presses */ public void actionPerformed(ActionEvent e){
String button = e.getActionCommand();
//System.out.printf("Button: %s\n", button); //for debugging
if (button.equals("New") )
newDrawing();
else if (button.equals("Open") )
openDrawing();
else if (button.equals("Save") )
saveDrawing();
else if (button.equals("Color") )
selectColor();
else if (button.equals("Reverse") )
reverseDrawing();
else if (button.equals("Quit") )
frame.dispose();
else{ //
currentAction = Action.valueOf(button); // converts the String to an Action.
}
} /** Sets the current color.
* Also changes the color of the Color button and sets the background color of the canvas */
private void selectColor(){
Color newColor = JColorChooser.showDialog(frame,"Choose Color for new shapes", currentColor);
if (newColor!=null){
currentColor=newColor;
colorButton.setBackground(currentColor);
}
} // Respond to mouse events
/** When mouse is pressed, remember the position in order to construct the Shape when
* the mouse is released. */
public void mousePressed(MouseEvent e) {
int x = e.getX(); int y = e.getY();
//System.out.printf("Pressed at (%d, %d)\n", x, y); //for debugging
pressedX = x;
pressedY = y;
} /** When the Mouse is released, depending on the currentAction,
* either construct the shape that was being drawn, or perform the
* action (delete or move) on the shape under the point where the mouse was pressed.*/

public void mouseReleased(MouseEvent e) {
int x = e.getX(); int y = e.getY();
//System.out.printf("Released at (%d, %d)\n", x, y); //for debugging
if (currentAction==Action.Move)
moveShape(pressedX, pressedY, x, y);
else if (currentAction==Action.Delete)
deleteShape(x, y);
else if (currentAction==Action.Push)
pushShapeBackward(x, y);
else if (currentAction==Action.Pull)
pullShapeForward(x, y);
else
addShape(pressedX, pressedY, x, y);
} public void mouseClicked(MouseEvent e) {} //needed to satisfy interface
public void mouseEntered(MouseEvent e) {} //needed to satisfy interface
public void mouseExited(MouseEvent e) {} //needed to satisfy interface
// Helper methods for implementing the button and mouse actions

/** Start a new drawing. */
public void newDrawing(){
shapes = new ArrayList<Shape>();
canvas.clear();
}
/** Open a file, and read all the shape descriptions into the current drawing. */
public void openDrawing(){
String fname = FileChooser.open();
if (fname==null) return;
try {
Scanner file = new Scanner(new File(fname));
//System.out.printf("Opening file %s\n", fname);
shapes = new ArrayList<Shape>();
while (file.hasNext()){
String shapetype = file.next().toLowerCase();
if (shapetype.equals("oval"))
shapes.add(new Oval(file));
else if (shapetype.equals("rectangle"))
shapes.add(new Rectangle(file));
if (shapetype.equals("line"))
shapes.add(new Line(file));
if (shapetype.equals("textshape"))
shapes.add(new TextShape(file));
else if (shapetype.equals("triangle"))
shapes.add(new Triangle(file));
else if (shapetype.equals("dot"))
shapes.add(new Dot(file));
}
render();
}
catch(IOException e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
} /** Save the current drawing to a file. */
public void saveDrawing(){
String fname =FileChooser.save();
if ( fname == null )
return;
try{
PrintStream f = new PrintStream( new File( fname ));
for ( Shape shape : shapes )
f.println( shape.toString());
f.close ();
}
catch(IOException ex){
System.out.println(ex.getMessage());
ex.printStackTrace();
}
}
/** Returns the shape under the position (x y), or null if no such shape */
public Shape findShape(int x, int y){
for (int i = shapes.size()-1; i>=0; i--){ // must go backwards, so can't use foreach
Shape shape = shapes.get(i);
if (shape.pointOnShape(x, y))
return shape;
}
return null; // no shape found at position
}
/** Moves the shape that was under the mousePressed position (pressedX, pressedY)
to where the mouse was released.
Ie, move it by (newX-pressedX) and (newY-pressedY)
*/
public void moveShape(int fromX, int fromY, int toX, int toY){
//System.out.printf("Moving shape under (%d, %d) to (%d, %d)\n", pressedX, pressedY, newX, newY); //for debugging
Shape shape = findShape(fromX, fromY);
if (shape!= null)
shape.moveBy((toX-fromX), (toY-fromY));
render();
} /** Deletes the shape that was under the mouseReleased position (x, y)
*/
public void deleteShape(int x, int y){ for ( Shape shape : shapes) {
if ( shape.pointOnShape(x, y ))
shapes.remove ( shape );
}
render();
}
/** Pull the shape under the mouse one position closer to the "front"
of the drawing */
public void pullShapeForward(int x, int y){
// System.out.printf("Pulling shape under (%d, %d) forward\n", x, y); //for debugging
// YOUR CODE HERE
Shape shape = findShape( x, y );
if (shape!=null ) {
int index = shapes.indexOf(shape);
if ( index< shapes.size()-1){
shapes.remove(index);
shapes.add( index+1,shape);
}
render();

}
}
/** Push the shape under the mouse one position further from the "front"
of the drawing */
public void pushShapeBackward(int x, int y){
//System.out.printf("Pushing shape under (%d, %d) backward\n", x, y); //for debugging
// YOUR CODE HERE
Shape shape = findShape(x, y );
if ( shape!=null ){
int index = shapes.indexOf(shape);
if( index > 0 )
shapes.remove( index);
shapes.add( index-1, shape);
}
render();

}

/** Reverse the order of the shapes in the drawing */
public void reverseDrawing(){ List<Shape>temp = new ArrayList<Shape>();
while ( shapes.size() > 0 ) {
temp.add ( shapes.remove(shapes.size()-1));
}
shapes= temp;
render();

}
/** Construct a new Shape object of the appropriate kind (depending on currentAction)
Uses the appropriate constructor of the Line, Rectangle, Oval, TextShape, or Triangle classes.
adds the shape it to the collection of shapes in the drawing, and
renders the shape on the canvas */
public void addShape(int x1, int y1, int x2, int y2){
//System.out.printf("Drawing shape %s, at (%d, %d)-(%d, %d)\n", currentAction, pressedX, pressedY, x, y); //for debugging
Shape shape = null;
if (currentAction==Action.Line)
shapes.add(new Line(x1, y1, x2, y2, currentColor));
if (currentAction==Action.Triangle)
shapes.add(new Triangle(x1, y1, x2, y2, currentColor));
if (currentAction==Action.Dot)
shapes.add(new Dot(x2, y2, currentColor));
else if (currentAction==Action.Text)
shapes.add(new TextShape(x2, y2, textField.getText(), currentColor));
else{
int left= Math.min(x1, x2);
int top= Math.min(y1, y2);
int width= Math.abs(x1 - x2);
int height= Math.abs(y1 - y2);
if (currentAction==Action.Rect)
shapes.add(new Rectangle(left, top, width, height, currentColor));
else if (currentAction==Action.Oval)
shapes.add(new Oval(left, top, width, height, currentColor));
}
render();
} public void render(){
canvas.clear(false);
for (Shape shape : shapes){
shape.render(canvas);
}
canvas.display();
} public static void main(String args[]){
new MiniDraw();
}}

Answer 2

////保存一个pb.java文件直接编译执行
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");
Size