想在panel中画一矩形，为啥画不出来呀？
import javax.swing.*;
import java.awt.*;
import javax.swing.border.*;

public class myclspaneltest extends JApplet
{
public void init()
{
Container mycontainer01=getContentPane();
                   myPanel mypanel02=new myPanel();
mycontainer01.setLayout(new FlowLayout());
mycontainer01.add(mypanel02);
}
}


class myPanel extends JPanel
{
public void paintComponent(Graphics g)
{
                super.paintComponent(g);
update(g);
}

public void update(Graphics g)
{
        g.drawOval(100,100,50,50);
    }
}

mycontainer01.setLayout(new FlowLayout());
mypanel02的父容器你设为FlowLayout，其大小是自动设定的。运行后，你会发现mypanel02是很小的，你要画(100,100,50,50)，已经超出了它的范围，当然看不到了。另外，重载paintComponent()方法也是可以的。
import javax.swing.*;
import java.awt.*;
import javax.swing.border.*;

/*


*/

public class myclspaneltest extends JApplet
{
public void init()
{
Container mycontainer01=getContentPane();
TitledBorder mytitleborder01=new TitledBorder("mypanel01 border");
JButton mybutton01=new JButton("Center");
JButton mybutton02=new JButton("This North");
JButton mybutton03=new JButton("This is a test");
JPanel mypanel01=new JPanel();
myPanel mypanel02=new myPanel();

mycontainer01.setLayout(new GridLayout());
mycontainer01.setSize(new Dimension(250, 200));
mypanel01.setLayout(new BorderLayout());
mypanel01.setBorder(mytitleborder01);
mypanel01.setBorder(BorderFactory.createLineBorder(Color.blue,2));
mypanel02.setBorder(BorderFactory.createLineBorder(Color.red,2));

mypanel01.add(mybutton01,BorderLayout.CENTER);
mypanel01.add(mybutton02,BorderLayout.NORTH);
mypanel02.add(mybutton03);
mycontainer01.add(mypanel01);
mycontainer01.add(mypanel02);
}
}


class myPanel extends JPanel
{
public void paintComponent(Graphics g)
{
                super.paintComponent(g);
update(g);
}

public void update(Graphics g)
{
        g.drawRect(100,100,50,60);
         }
}