在java中实现图形学中的椭圆算法

      有同学向我要在java中实现图形学中的椭圆算法，画直线的算法的程序，在此就献丑了，把上大学时用java写的源代码给先学者做个参考，下面是实现椭圆的算法

/*author computer np
 *test date
 *(300,100)(400,100)
 *
*/
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class Lipse
{
 public static void main(String[] args)
 {
  new MainFrame();
 }
}
class MainFrame extends JFrame implements ActionListener
{
 JPanel pane=new JPanel();
 JTextField T_a,T_b;
 JButton Draw,Show;
 JLabel L_a,L_b;
 int a,b;
 MainFrame()
 {
  super("DrawLipse Window");
  Container con=this.getContentPane();
  con.setLayout(null);
  
  pane.setBounds(20,20,850,550);
  pane.setBackground(new Color(100,156,200));
  con.add(pane);
  
  L_a=new JLabel("请输入长半径:a");
  L_a.setBounds(180,580,100,20);
  con.add(L_a);
  
  L_b=new JLabel("请输入短半径:b");
  L_b.setBounds(180,630,100,20);
  con.add(L_b);
  
  
  T_a=new JTextField();
  T_a.setBounds(300,580,50,20);
  con.add(T_a);
  
  T_b=new JTextField();
  T_b.setBounds(300,630,50,20);
  con.add(T_b);
  
  Draw=new JButton("画椭圆");
  Draw.setBounds(550,580,90,30);
  Draw.addActionListener(this);
  con.add(Draw);
  
  Show=new JButton("显示坐标");
  Show.setBounds(550,620,90,30);
  Show.addActionListener(this);
  con.add(Show);
  
  this.addWindowListener(new CloseWindow());
  this.setBounds(20,20,900,700);
  this.setVisible(true);
  this.setResizable(false);
  
 }/*MainFrame()*/
 public void actionPerformed(ActionEvent e)
 {
     if(e.getSource()==Draw)
     {
      a=Integer.parseInt(T_a.getText().trim());
      b=Integer.parseInt(T_b.getText().trim());
      Line line=new Line(this);
      line.drawLipse(a,b);
     }
     if(e.getSource()==Show)
     {
       Graphics g1=this.pane.getGraphics();
          g1.setColor(Color.PINK);
          g1.drawLine(0,300,920,300);//----x---
          g1.drawLine(410,0,410,720);//----y---
          g1.dispose();
     }
  
 }/*method actionPerformed*/
}
class Line
{
 MainFrame jb;
 Line(MainFrame jb)
 {
  this.jb=jb;
 }
 public void drawLipse(int a,int b)
 {
  int x,y;
  double d1,d2;
  x=0;  y=b;
  d1=b*b+a*a*(-b+0.25);
  Graphics g=jb.pane.getGraphics();
  g.setColor(Color.red);
  g.drawLine(x+410,y+300,x+410,y+300);
  g.drawLine(-x+410,-y+300,-x+410,-y+300);
  g.drawLine(-x+410,y+300,x+410,-y+300);
  g.drawLine(x+410,-y+300,x+410,-y+300);
  try
  {
   while(b*b*(x+1)<a*a*(y-0.5))
               {
            if(d1<=0)
              {
              d1+=b*b*(2*x+3);
              x++;
              }
              else
              {
              d1+=(b*b*(2*x+3)+a*a*(-2*y+2));
              x++;
              y--;
              }
              g.drawLine(x+410,y+300,x+410,y+300);
              g.drawLine(-x+410,-y+300,-x+410,-y+300);
              g.drawLine(-x+410,y+300,x+410,-y+300);
              g.drawLine(x+410,-y+300,x+410,-y+300);
              Thread.sleep(30);
         }// top of while 
     }catch(Exception e){}
    
  d2=b*b*(x+0.5)*(x+0.5)+a*a*(y-1)*(y-1)-a*a*b*b;
  try
  {
   while(y>0)
      {
     if(d2<=0)
       {
       d2+=b*b*(2*x+2)+a*a*(-2*y+3);
       x++;
          y--;
        }
        else
        {
        d2+=a*a*(-2*y+3);
        y--;
        }
        g.drawLine(x+410,y+300,x+410,y+300);
           g.drawLine(-x+410,-y+300,-x+410,-y+300);
           g.drawLine(-x+410,y+300,x+410,-y+300);
           g.drawLine(x+410,-y+300,x+410,-y+300);
           Thread.sleep(30);
        }/* bottom of while*/
   
     }catch(Exception e){}
  
 } /*DrawLipse*/ 
  
}
class CloseWindow extends WindowAdapter
{
 public void windowClosing(WindowEvent e)
 {
  System.exit(0);
 }
}