如何用Graphics类画三角形？

Question

请问如何用Graphics类画三角形？

Answer 1

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.geom.GeneralPath;import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;@SuppressWarnings("serial")
public class TrianglePainter extends JPanel {
    private Triangle triangle;    public TrianglePainter() {
        triangle = new Triangle(new Point(20, 20), new Point(100, 100), new Point(10, 100));
    }    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        triangle.draw(g2d);
        
        g2d.translate(150, 150);
        triangle.fill(g2d);
    }    private static void createGuiAndShow() {
        JFrame frame = new JFrame("三角形");
        frame.getContentPane().add(new TrianglePainter());        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 400);
        frame.setAlwaysOnTop(true);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                createGuiAndShow();
            }
        });
    }
}// 定义一个三角形类
class Triangle {
    private Point p1;
    private Point p2;
    private Point p3;    private GeneralPath path;    // 使用三个点构建一个三角形
    public Triangle(Point p1, Point p2, Point p3) {
        this.p1 = p1;
        this.p2 = p2;
        this.p3 = p3;
        this.path = buildPath();
    }    // 绘制三角形边
    public void draw(Graphics2D g2d) {
        g2d.draw(path);
    }    // 填充三角形
    public void fill(Graphics2D g2d) {
        g2d.fill(path);
    }    // 创建三角形外形的路径
    private GeneralPath buildPath() {
        path = new GeneralPath();
        path.moveTo(p1.x, p1.y);
        path.lineTo(p2.x, p2.y);
        path.lineTo(p3.x, p3.y);
        path.closePath();        return path;
    }
}

Answer 2

class PainterPanel extends JPanel implements MouseListener{
    int shape=-1; //图案类型
    Point[] point=new Point[2]; //记录鼠标拖动的起始点和终点
    //构造函数**********************************************
    public PainterPanel(){
           super(); //调用父类构造函数
           this.setBackground(Color.white); //设置背景颜色(JPanel成员） 其他成员对绘图没有实质性的帮助
        point[0]=new Point(-1,-1); //初始化变量
        point[1]=new Point(-1,-1);
           addMouseListener(this); //增加鼠标事件
    }
   //构造函数************************************************
    public void mouseReleased(MouseEvent e){ //鼠标释放事件
           point[1]=new Point(e.getX(),e.getY()); //设置终点位置
           repaint(); //重绘屏幕
    }    public void mouseEntered(MouseEvent e){}
    public void mouseExited(MouseEvent e){}
    public void mouseClicked(MouseEvent e){}    public void mousePressed(MouseEvent e){ //鼠标按下时事件
           point[0]=new Point(e.getX(),e.getY()); //设置起始点位置
    }    public void paint(Graphics g){
           super.paint(g);
           switch (shape){ //根据shape值绘制图形
            case 0:
             g.drawLine(point[0].x,point[0].y,point[1].x,point[1].y); //绘线
             break;            case 1:
             int width=point[1].x-point[0].x;
             int height=point[1].y-point[0].y;
             g.drawOval(point[0].x,point[0].y,width,height); //绘椭圆
             break;            case 2:
             width=point[1].x-point[0].x;
             height=point[1].y-point[0].y;
             g.drawRect(point[0].x,point[0].y,width,height); //绘矩形
             break;
           }
    }
    public void drawShape(int shape)
    {
           this.shape=shape;
    }
}
目前写的代码是这样 我不知道如何得到3个不同的点的坐标画3跳线

Answer 3

想出来了 加个鼠标单击事件 
import java.awt.*;
import java.awt.event.*;//包含MouseListener
import javax.swing.*;
import javax.swing.event.*;
class PainterPanel extends JPanel implements MouseListener{
    int shape=-1; //图案类型
    Point[] point=new Point[3]; //记录鼠标拖动的起始点和终点
    //构造函数**********************************************
    public PainterPanel(){
           super(); //调用父类构造函数
           this.setBackground(Color.white); //设置背景颜色(JPanel成员） 其他成员对绘图没有实质性的帮助
        point[0]=new Point(-1,-1); //初始化变量
        point[1]=new Point(-1,-1);
           addMouseListener(this); //增加鼠标事件
    }
   //构造函数************************************************
    public void mouseReleased(MouseEvent e){ //鼠标释放事件
           point[1]=new Point(e.getX(),e.getY()); //设置终点位置
           repaint(); //重绘屏幕
    }    public void mouseEntered(MouseEvent e){}
    public void mouseExited(MouseEvent e){}    public void mouseClicked(MouseEvent e)
    { point[2]=new Point (e.getX(),e.getY());
    }    
    public void mousePressed(MouseEvent e)
    { //鼠标按下时事件
           point[0]=new Point(e.getX(),e.getY()); //设置起始点位置
    }    public void paint(Graphics g){
           super.paint(g);
           switch (shape){ //根据shape值绘制图形
            case 0:
             g.drawLine(point[0].x,point[0].y,point[1].x,point[1].y); //绘线
             break;            case 1:
             int width=point[1].x-point[0].x;
             int height=point[1].y-point[0].y;
             g.drawOval(point[0].x,point[0].y,width,height); //绘椭圆
             break;            case 2:
             width=point[1].x-point[0].x;
             height=point[1].y-point[0].y;
             g.drawRect(point[0].x,point[0].y,width,height); //绘矩形
             break;           case 3:            g.drawLine(point[0].x,point[0].y,point[1].x,point[1].y);
            g.drawLine(point[0].x,point[0].y,point[2].x,point[2].y);
            g.drawLine(point[2].x,point[2].y,point[1].x,point[1].y);
            break;
           }
    }
    public void drawShape(int shape)
    {
           this.shape=shape;
    }
}
public class PainterDemo extends JFrame{
    JToggleButton[] button=new JToggleButton[4]; //按钮组
    PainterPanel painter=new PainterPanel(); //绘图面板  上面构造了
    public PainterDemo(){
           super("Java随手画"); //调用父类构造函数
           String[] buttonName={"直线","椭圆","矩形"," 三角形"}; //按钮文字
           DrawShapeListener buttonListener=new DrawShapeListener(); //按钮事件
           JToolBar toolBar=new JToolBar(); //实例化工具栏
           ButtonGroup buttonGroup=new ButtonGroup(); //实例化按钮组           for (int i=0;i<button.length;i++){
                   button[i]=new JToggleButton(buttonName[i]); //实例化按钮
                   button[i].addActionListener(buttonListener); //增加按钮事件处理
                   buttonGroup.add(button[i]); //增加按钮到按钮组
                   toolBar.add(button[i]); //增加按钮到工具栏
           }           Container container=getContentPane(); //得到窗口容器
           container.add(toolBar,BorderLayout.NORTH); //增加组件到容器上
           container.add(painter,BorderLayout.CENTER);
           setSize(300,200); //设置窗口尺寸
           setVisible(true); //设置窗口为可视
           setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //关闭窗口时退出程序
    }
//内部类
    class DrawShapeListener implements ActionListener{ //按钮事件处理
           public void actionPerformed(ActionEvent e){
            for (int i=0;i<button.length;i++){
                 if (e.getSource()==button[i]){ //判断来自于哪个按钮
                      painter.drawShape(i); //绘制图形
                 }
            }
           }
    }    public static void main(String[] args){
           new PainterDemo();
    }
}