import java.awt.*;
import javax.swing.*;
class test5{
public static void main(String []args){
new ax();
}
}
class ax extends JFrame{
public ax(){
Container c = getContentPane();  //画板
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //关闭退出
setBounds(200,100,400,300);    //设置大小
show();  
pack();                      //显示
jp3 a =  new jp3(Color.red);    //声明面板
c.add(a,BorderLayout.NORTH);// 加入面板
}   
}
class jp3 extends JPanel{
public jp3(Color x){
  setBackground(x);  // 设置背景颜色
  setPreferredSize(300,300);  //设置大小？？？？？不起作用
JButton jb = new JButton(); // JButton 
jb.setBackground(Color.white); //color for JButton.
jb.setPreferredSize(new Dimension(200,10));
JRadioButton jr = new JRadioButton();   //JRadioButton
jr.setBackground(Color.blue);   // color for JRadioButton
jr.setPreferredSize(new Dimension(20,100));
add(jr);
add(jb);

}
}