使用Java绘制五星红旗

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　　RT,效果&代码：

/**
    使用Java2D绘制五星红旗
    五星红旗的绘制标准见百度百科: http://baike.baidu.com/view/5163.htm
    注意: 该处对于第一颗小星的位置说明有误,应将“左五右十”改成“左十右五”
    @author  Eastsun
    @version 2008/10/17 1.0
*/
import javax.swing.*;
import java.awt.geom.*;
import java.awt.*;

public class NationalFlag extends JPanel{
    
    public static void main(String[] args){
        JFrame frame = new JFrame("五星红旗 By Eastsun");
        frame.getContentPane().add(new NationalFlag(600));
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
    
    /**
       创建一个五角星形状.
       该五角星的中心坐标为(sx,sy),中心到顶点的距离为radius,其中某个顶点与中心的连线的偏移角度为theta(弧度)
       @return pentacle 一个☆
    */
    public static Shape createPentacle(double sx,double sy,double radius,double theta){
        final double arc = Math.PI/5;
        final double rad = Math.sin(Math.PI/10)/Math.sin(3*Math.PI/10);
        GeneralPath path = new GeneralPath();
        path.moveTo(1,0);
        for(int idx = 0;idx < 5;idx ++){
            path.lineTo(rad*Math.cos((1+2*idx)*arc),rad*Math.sin((1+2*idx)*arc));
            path.lineTo(Math.cos(2*(idx+1)*arc),Math.sin(2*(idx+1)*arc));
        }
        path.closePath();
        AffineTransform atf = AffineTransform.getScaleInstance(radius,radius);
        atf.translate(sx/radius,sy/radius);
        atf.rotate(theta);
        return atf.createTransformedShape(path);
    }
    
    private int width,height;
    private double maxR = 0.15, minR = 0.05;
    private double maxX = 0.25, maxY = 0.25;
    private double[] minX = {0.50, 0.60, 0.60, 0.50};
    private double[] minY = {0.10, 0.20, 0.35, 0.45};
    
    /**
       创建一个宽度为width的国旗
    */
    public NationalFlag(int width){
        this.width =  width/3*3;
        this.height = width/3*2;
        setPreferredSize(new Dimension(this.width,this.height));
    }
    
    protected void paintComponent(Graphics g){
        Graphics2D g2d = (Graphics2D)g;
        
        //画旗面
        g2d.setPaint(Color.RED);
        g2d.fillRect(0,0,width,height);
        
        //画大☆
        double ox = height*maxX, oy = height*maxY;
        g2d.setPaint(Color.YELLOW);
        g2d.fill(createPentacle(ox,oy,height*maxR,-Math.PI/2));
        
        //画小★
        for(int idx =0;idx < 4;idx ++){
            double sx = minX[idx]*height, sy = minY[idx]*height;
            double theta = Math.atan2(oy-sy,ox-sx);
            g2d.fill(createPentacle(sx,sy,height*minR,theta));
        }
    }
}