package com.sunzhiyan;import java.awt.*;import java.awt.event.*;import javax.swing.*;public class Demo_1 extends JFrame{	/**	 * @param args	 */	JButton button1,button2,button3;	public static void main(String[] args) {		// TODO Auto-generated method stub 		Demo_1 demo = new Demo_1("hellow");			       	}	public Demo_1(String name){	    JButton button1 = new JButton("123"); 	    JButton button2 = new JButton("456"); 	    JButton button3 = new JButton("789"); 	    this.add(button1);	    this.add(button2);	    this.add(button3);            //启动流式布局，并且左浮动	    this.setLayout(new FlowLayout(FlowLayout.LEFT));	    		this.setTitle(name);		this.setSize(400,400);		this.setLocation(100,100);		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);		//this.setLayout(null);		//this.setResizable(false);		//this.setEnabled(true);	    this.setVisible(true);    	}}
查JDK手册，可知 JButton 

java.lang.Object 

java.awt.Component 

java.awt.Container 

javax.swing.JComponent 

javax.swing.AbstractButton 

javax.swing.JButton
内部是这样的一个多继承的方式，因此底层的同时也能够使用上 层的方法和属性