JAVA中绘制多边形的算法

  1 package lzy.di9zhang;
  2 
  3 import java.awt.BorderLayout;
  4 import java.awt.Graphics;
  5 import java.awt.Point;
  6 import java.awt.event.ActionEvent;
  7 import java.awt.event.ActionListener;
  8 import java.awt.event.FocusEvent;
  9 import java.awt.event.FocusListener;
 10 
 11 import javax.swing.JButton;
 12 import javax.swing.JFrame;
 13 import javax.swing.JLabel;
 14 import javax.swing.JPanel;
 15 import javax.swing.JTextField;
 16 
 17 public class Shiyan4 extends JFrame implements ActionListener, FocusListener {
 18     private JLabel jl;
 19     private JTextField jtf;
 20     private JButton jb;
 21     private JPanel jp2;
 22     private MyPanel mp;
 23 
 24     public Shiyan4() {
 25         jl = new JLabel("请输入正多边形的边数：");
 26         jtf = new JTextField(10);
 27         jtf.addFocusListener(this);
 28         jb = new JButton("确定");
 29         jb.addActionListener(this);
 30         mp = new MyPanel();
 31         jp2 = new JPanel();
 32         jp2.add(jl);
 33         jp2.add(jtf);
 34         jp2.add(jb);
 35         this.add(mp);
 36         this.add(jp2, BorderLayout.SOUTH);

 37         this.setSize(500, 500);
 38         this.setVisible(true);
 39         this.setDefaultCloseOperation(EXIT_ON_CLOSE);
 40     }
 41 
 42     public static void main(String[] args) {
 43         Shiyan4 shiyan4 = new Shiyan4();
 44     }
 45 
 46     @Override
 47     public void actionPerformed(ActionEvent e) {
 48         if (e.getSource() == jb) {
 49             String bianshu = jtf.getText();
 50             mp.bianshu = Integer.parseInt(bianshu);
 51             mp.repaint();
 52         }
 53     }
 54 
 55     @Override
 56     public void focusGained(FocusEvent e) {
 57         if (e.getSource() == jtf) {
 58             jtf.setText("");
 59         }
 60     }
 61 
 62     public void focusLost(FocusEvent e) {
 63     }
 64 }
 65 
 66 class MyPanel extends JPanel {
 67     int bianshu;
 68     private int bianshuMax = 20;
 69     private int[] x = new int[bianshuMax];
 70     private int[] y = new int[bianshuMax];
 71     MyPolygon mplg = new MyPolygon(x, y);
 72 
 73     public void paint(Graphics g) {
 74         g.clearRect(0, 0, this.getWidth(), this.getHeight());//因为repaint不调用update，所以自己清空面板
 75         if (bianshu <= bianshuMax) {
 76             mplg.posOfPoint(bianshu);
 77             g.drawPolygon(x, y, bianshu);
 78         } else {
 79             bianshuMax += 20;
 80             x = new int[bianshuMax];
 81             y = new int[bianshuMax];
 82             mplg = new MyPolygon(x, y);
 83             paint(g);
 84         }
 85     }
 86 }
 87 
 88 class MyPolygon {// 求正多边形的顶点坐标
 89     private int[] x;
 90     private int[] y;
 91     private int startX;// 顶点的X坐标
 92     private int startY;// 顶点的Y坐标
 93     private int r;// 外接圆的半径
 94 
 95     public MyPolygon(int[] x, int[] y) {
 96         this.x = x;
 97         this.y = y;
 98         startX = 200;
 99         startY = 10;
100         r = 200;
101     }
102 
103     public void posOfPoint(int bianshu) {
104         x[0] = startX;
105         y[0] = startY;
106         Point p = new Point();
107         for (int i = 1; i < bianshu; i++) {
108             p = nextPoint(((2 * Math.PI) / bianshu) * i);
109             x[i] = p.x;
110             y[i] = p.y;
111         }
112     }
113 
114     public Point nextPoint(double arc) {// arc为弧度，在顶点处建立直角坐标系，用r和arc确定下一个点的坐标
115         Point p = new Point();
116         p.x = (int) (x[0] - r * Math.sin(arc));
117         p.y = (int) (y[0] + r - r * Math.cos(arc));
118         return p;
119     }
120 }

核心代码：
public　　Point 　　nextPoint(double arc) {// arc为弧度，在顶点（x[0],y[0]）处建立直角坐标系，

　　　　　　　　　　　　　　　　　　　　　　//用 r 和 arc 确定下一个点的坐标。
　　　　　　　　　　Point p = new Point();
　　　　　　　　　　 p.x = (int) (x[0] - r * Math.sin(arc));
　　　　　　　　　　 p.y = (int) (y[0] + r - r * Math.cos(arc));
　　　　　　　　　　 return p;
　　　　　　　　　　 }

运行界面：