Java GUI中改變窗體的背影圖檔

package cn.edu.hactcm;

import java.awt.borderlayout;

import java.awt.graphics;

import javax.swing.imageicon;

import javax.swing.jbutton;

import javax.swing.jframe;

import javax.swing.jpanel;

import javax.swing.jtextfield;

public class app extends jframe {

 private jtextfield textfield;

 public app() {

  getcontentpane().setlayout(new borderlayout(0, 0));

  jpanel panel = new imagepanel();

  getcontentpane().add(panel);

  panel.setlayout(null);

  jbutton btnnewbutton = new jbutton("new button");

  btnnewbutton.setbounds(108, 234, 93, 23);

  panel.add(btnnewbutton);

  textfield = new jtextfield();

  textfield.setbounds(214, 176, 96, 19);

  panel.add(textfield);

  textfield.setcolumns(10);

  setsize(460, 350);

  setdefaultcloseoperation(exit_on_close);

  setvisible(true);

 }

 public static void main(string[] args) {

  new app();

 class imagepanel extends jpanel {

  protected void paintcomponent(graphics g) {

   super.paintcomponent(g);

   string path = imagepanel.class.getclassloader().getresource("zlp.jpg").getpath();

   imageicon icon = new imageicon(path);

   g.drawimage(icon.getimage(), 0, 0, null);

  }

}