画椭圆可以通过画矩形及其内切椭圆实现，示例代码如下
如果只需要椭圆，则无需g2.draw(rect)
class DrawPanel extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g)
Graphics2D g2 = (Graphics2D) g
// 画矩形
double leftX = 100
double topY = 100
double width = 200
double height = 150
Rectangle2D rect = new Rectangle2D.Double(leftX, topY, width, height)
g2.draw(rect)
// 画rect的内切椭圆
Ellipse2D ellipse = new Ellipse2D.Double()
ellipse.setFrame(rect)
g2.draw(ellipse)
}
}
以下代码，将输出一个椭圆，再有问题，我可远程助你。如下：
/***(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)
}
}
