我安装了JDK，在文本编辑器中定的代码
在JFrame中加入了三个按钮，进行窗口，是空白的
在窗口上要按下鼠标才能显示按钮，
并且只显示最后的增加的铵钮，请问这是为什么
要如何时写代码？
import javax.swing.*;
public class c extender JFrame{
JButton jb1 = new JButton("abc1");
JButton jb2 = new JButton("abc2");
JButton jb3 = new JButton("abc3");
public c (){

super("titel")
add(jb1);
add(jb2);
add(jb3);

}
public static void main(String arg[]){
c cc = new c();
cc.show();
}
}

import javax.swing.*; //插入javax.swing包
import java.awt.*; //插入java.awt包

class FrameTest extends JFrame
{
public FrameTest() //创建构造符函数
{
super("窗体标题"); //创建JFrame类对象
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true); //设置窗体可见
setSize(240,90); //设置窗体大小
}
}
class ButtonTest extends FrameTest
{
JButton buttonObj1;
JButton buttonObj2;
public ButtonTest()
{
buttonObj1=new JButton("按钮1");
buttonObj2=new JButton("按钮2");
getContentPane().add("West",buttonObj1);
getContentPane().add("East",buttonObj2);
}
}
public class J03_Button extends ButtonTest
{
public static void main(String[] args)
{
new J03_Button();
}
}

package test;
import java.awt.*;
import javax.swing.*;
/**
 * @author hyvin
 *
 * TODO To change the template for this generated type comment go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
public class JButtonDemo extends JFrame {
 JButton button1;
 JButton button2;
 JPanel panel1;
 JPanel panel2;
    JPanel contentPane;
    GridLayout gridLayout;
 public JButtonDemo(){
  try {
   setDefaultCloseOperation(EXIT_ON_CLOSE);
   jinit();
  } catch (RuntimeException e) {
   e.printStackTrace();
  }  
 }
 private void jinit(){
  contentPane = (JPanel) getContentPane();
  GridLayout gridLayout = new GridLayout();
  contentPane.setLayout(gridLayout);
  button1 = new JButton(\"button1\");
  button2 = new JButton(\"button2\");
  panel1 = new JPanel();
  panel2 = new JPanel();
  panel1.add(button1);
  panel2.add(button2);
  contentPane.add(panel1);
  contentPane.add(panel2);
 }
 public static void main(String[] args) {
  JButtonDemo jbd = new JButtonDemo();
  jbd.setTitle(\"Demo\");
  jbd.pack();
  jbd.setVisible(true);
 }
}

因为你没写布局，所以只显示最后一个