Line 

マウスをクリックすると多角形になります。　

/*
    A basic extension of the java.applet.Applet class
*/

import java.awt.*;
import java.applet.*;

public class Applet1 extends Applet
{
double x1,y1,x2,y2;
double rad=Math.PI/180,leng=50,decrese=10,ang,n,j;
int k=3;

    public void init()
    {
        // Take out this line if you don't use symantec.itools.net.RelativeURL 

or symantec.itools.awt.util.StatusScroller
        symantec.itools.lang.Context.setApplet(this);
    

        // This code is automatically generated by Visual Cafe when you add
        // components to the visual environment. It instantiates and initializes
        // the components. To modify the code, only use code syntax that matches
        // what Visual Cafe can generate, or Visual Cafe may be unable to back
        // parse your Java file into its visual environment.
        //{{INIT_CONTROLS
        setLayout(null);
        setSize(756,478);
        

        add(label1);
        label1.setBackground(java.awt.Color.green);
        label1.setBounds(492,312,24,24);
        button1.setLabel("Clear");
        add(button1);
        button1.setBackground(java.awt.Color.lightGray);
        button1.setBounds(492,348,60,24);
        //}}
    

        //{{REGISTER_LISTENERS
        SymMouse aSymMouse = new SymMouse();
        this.addMouseListener(aSymMouse);
        SymAction lSymAction = new SymAction();
        button1.addActionListener(lSymAction);
        //}}
    }
    

    //{{DECLARE_CONTROLS
    java.awt.Label label1 = new java.awt.Label();
    java.awt.Button button1 = new java.awt.Button();
    //}}
    

    public void update(Graphics g)
    {
    paint(g);
    }

    public void paint(Graphics g) { 

//以下のコードを自分が作ったのですが、、、、、

三角形の場合を考えるとこのコードがわかると思います。
    x1=300;
    y1=300;
    for(j=3;j<=k;j=j+1) {
    for(n=1;n<=j;n=n+1) {
    ang=360/j*n;
    x2=x1 +leng*Math.cos(rad*ang);
    y2=y1 -leng*Math.sin(rad*ang);
    g.setColor(Color.blue);
    g.drawLine((int)x1,(int)y1,(int)x2,(int)y2);
    x1=x2;
    y1=y2;
    }
    }
    

    
    class SymMouse extends java.awt.event.MouseAdapter
    {
        public void mouseClicked(java.awt.event.MouseEvent event)
        {
            Object object = event.getSource();
            if (object == Applet1.this)
                Applet1_MouseClicked(event);
        }
    }

    void Applet1_MouseClicked(java.awt.event.MouseEvent event)
    {
        // to do: code goes here.
        k=k+1;
        

        label1.setText(" "+k);
        repaint();
        

    }

    class SymAction implements java.awt.event.ActionListener
    {
        public void actionPerformed(java.awt.event.ActionEvent event)
        {
            Object object = event.getSource();
            if (object == button1)
                button1_ActionPerformed(event);
        }
    }

    void button1_ActionPerformed(java.awt.event.ActionEvent event)
    {
        // to do: code goes here.
        Graphics g=getGraphics();
        g.clearRect(0,0,getSize().width,getSize().height);
        k=2;
        

        label1.setText("");     
    }
}

このアップレットは　"技術評論社　

Visual Basic 5.0 中級テクニック編"　を参考にしました。

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