package day11;

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.image.ImageObserver;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class MyQQTest implements ImageObserver {
    ImageIcon iconimage1;

    public static void main(String[] args) {
        new MyQQTest().Test();
    }
   
    public void Test(){
        JFrame frame  = new JFrame();
        JPanel p1 = new JPanel();
        JPanel p2 = new JPanel();
        JPanel p3 = new JPanel();
        JPanel p4 = new JPanel();
        JPanel p5 = new JPanel();
        GridLayout gl = new GridLayout(2,1);
        JButton b1 = new JButton("免费注册");
        JButton b2 = new JButton("忘记密码");
        JButton b3 = new JButton("登陆");
        JCheckBox cb1 = new JCheckBox("自动登录");
        JCheckBox cb2 = new JCheckBox("记住密码");
        JLabel lb1 = new JLabel("QQ号码: ");
        JTextField tf1 = new JTextField(15);
        JLabel lb2 = new JLabel("密     码：");
        JLabel lb3 = new JLabel("考试给学生扣分是违法的，刑法规定：利用他人无知造成他人损失的行为就是欺诈罪。");
        JTextField tf2 = new JTextField(15);
        
        p1.setLayout(gl);
        p1.add(p3);
        p1.add(p4);
        p3.add(lb1);
        p3.add(tf1);
        p3.add(b1);
        p4.add(lb2);
        p4.add(tf2);
        p4.add(b2);
        frame.add(p1,BorderLayout.NORTH);
        p2.add(b3);
        frame.add(p2);
        p5.add(lb3);
        frame.add(p5,BorderLayout.SOUTH);
        
        frame.setBounds(100,150,550,350);
        ImageIcon iconimage = new ImageIcon("src\\day11\\4.jpg");//这个是主题
        iconimage1 = new ImageIcon("src\\day11\\3.jpg");//想把这个图片加入frame界面
        frame.paintComponents(null);
        Image image = iconimage.getImage();
        frame.setIconImage(image);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
    public void paintComponent(Graphics g){
        
        g.drawImage(iconimage1.getImage(),0,0,this.getWidth(),this.getHeight(),this);
        
    }

    private int getHeight() {
        // TODO Auto-generated method stub
        return 0;
    }

    private int getWidth() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public boolean imageUpdate(Image img, int infoflags, int x, int y,
            int width, int height) {
        // TODO Auto-generated method stub
        return false;
    }

   
   

}

你应该把这个icon赋给一个label，这样就可以显示了。因为你的按钮也是要用图片美化的。

Icon ic1 = new ImageIcon("图片路径");
JLabel jl2 = new JLabel(ic1);

然后在panel里面add这个JLabel

要将窗体 Frame 设置为可视的窗体，因为工具中默认的是看不见的窗体。
在新建窗体后设置好其他属性以后记得将窗体设置为可视即可。
this.setVisible(true);