package com.http;import java.awt.*;import javax.swing.*;public class TestSwing2{//创建了一个能够绘制的组件class HelloWorldComponent extends JComponent{    public static final int MESSAGE_X = 75;    public static final int MESSAGE_Y = 100;        private static final int DEFAULT_WIDTH = 300;    private static final int DEFAULT_HEIGHT = 200;        public void paintComponent(Graphics g)    {        g.drawString("hello world",MESSAGE_X,MESSAGE_Y);    }        public Dimension getPreferredSize()    {        return new Dimension(DEFAULT_WIDTH,DEFAULT_HEIGHT);    }}
//添加内容到frameclass HelloWorldFrame extends JFrame{    public HelloWorldFrame()    {        add(new HelloWorldComponent());        pack();    }}public static void main(String[] argvs){    EventQueue.invokeLater(new Runnable()    {        public void run()        {            
　　　　　　　//在实例化内部类时，需要先实例化外部类            JFrame frame = new TestSwing2().new HelloWorldFrame();            frame.setTitle("hello world");            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);            frame.setVisible(true);        }    });    }}