JAVA GUI自定义JPanel画板背景

import java.awt.Graphics; import javax.swing.ImageIcon; import javax.swing.JFrame; import javax.swing.JPanel;  public class GUITest {    private static JFrame jframe; //声明一个窗体    private JPanel jpanel;     //声明一个画板      public GUITest(){       //构造方法      jframe = new JFrame();      init();    }      private void init(){      jframe.setTitle("测试");      jpanel = new JPanel(){//关键代码，就是重写了paint的一个方法         @Override         protected void paintComponent(Graphics g) {           super.paintComponent(g);           ImageIcon img = new ImageIcon(GUITest.class.getResource("bg.png"));           /**           * bg.PNG这个地方换成自己的图片           * 此处使用的相对路径，bg.png跟该测试类在同一路径下           * 不过建议使用相对路径避免使用绝对路径           */           img.paintIcon(this, g, 0, 0);         }      };      jpanel.setOpaque(true);      jframe.setBounds(200, 200, 500, 400); //设置显示位置距离左边200像素距离上边200像素及屏幕大小500*400            jframe.add(jpanel); //添加画板到窗体            jframe.setVisible(true); //设置显示界面    }      public static void main(String[] args) {       new GUITest();      // 实例化对象     } } 

import java.awt.Graphics; import java.awt.GridBagConstraints; import java.awt.GridBagLayout; import java.awt.Insets; import javax.swing.ImageIcon; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; import javax.swing.JPasswordField; import javax.swing.JTextField;  public class GUIT {   //声明窗体，面板及控件   private static JFrame jframe;   private JLabel jlabel,jlabel1;   private GridBagLayout gridbag;   private GridBagConstraints constraints;   private JTextField jtfield1;   private JPasswordField jpfield1;   private JButton jbutton1,jbutton2,jbutton3;   private JPanel jpanel;      public GUIT(){     jframe = new JFrame();     jlabel = new JLabel();     jlabel1 = new JLabel();     jtfield1 = new JTextField();     jpfield1 = new JPasswordField();     gridbag = new GridBagLayout();     jbutton1 = new JButton();     jbutton2 = new JButton();     jbutton3 = new JButton();     init();   }      /**    * init()初始化并显示界面    */   private void init(){     jframe.setTitle("登录");     /**      * 设置JPanel背景      */     jpanel = new JPanel(){       @Override       protected void paintComponent(Graphics g) {         super.paintComponent(g);         ImageIcon img = new ImageIcon(GUITest.class.getResource("ddmbg.jpg"));         img.paintIcon(this, g, 0, 0);       }     };     //为JLabel,JButton初始化文本     jlabel.setText("用户名：");     jlabel1.setText("密  码：");     jbutton1.setText("登录");     jbutton2.setText("退出");     jbutton3.setText("注册");        //设置显示位置及屏幕大小500*400     jframe.setBounds(450, 240, 400, 240);     //jpanel采用GridBagLayout布局管理器     jpanel.setOpaque(false);     jpanel.setLayout(gridbag);          //初始化用户名label，并添加该控件到画板     constraints = getGridBagConstraints(0,0,1,1,0,0,GridBagConstraints.CENTER,GridBagConstraints.NONE,new Insets(10,0,10,0),0,0);     gridbag.setConstraints(jlabel, constraints);     jpanel.add(jlabel);          //初始化用户名文本框，并添加该组件到画板     constraints = getGridBagConstraints(1,0,1,1,0,0,GridBagConstraints.CENTER,GridBagConstraints.NONE,new Insets(10,0,10,0),100,0);     gridbag.setConstraints(jtfield1, constraints);     jpanel.add(jtfield1);           //初始化密码label     constraints = getGridBagConstraints(0,1,1,1,0,0,GridBagConstraints.CENTER,GridBagConstraints.NONE,new Insets(10,0,10,0),0,0);     gridbag.setConstraints(jlabel1, constraints);     jpanel.add(jlabel1);         //初始化密码文本框     constraints = getGridBagConstraints(1,1,1,1,0,0,GridBagConstraints.CENTER,GridBagConstraints.NONE,new Insets(10,0,10,0),100,0);     gridbag.setConstraints(jpfield1, constraints);     jpanel.add(jpfield1);         //初始化注册按钮，并添加该控件到画板     constraints = getGridBagConstraints(0,2,1,1,0,0,GridBagConstraints.CENTER,GridBagConstraints.NONE,new Insets(10,0,10,0),0,0);     gridbag.setConstraints(jbutton3, constraints);     jpanel.add(jbutton3);        //初始化登录按钮     constraints = getGridBagConstraints(1,2,1,1,0,0,GridBagConstraints.CENTER,GridBagConstraints.NONE,new Insets(10,0,10,0),0,0);     gridbag.setConstraints(jbutton1, constraints);     jpanel.add(jbutton1);        //初始化退出按钮     constraints = getGridBagConstraints(2,2,1,1,0,0,GridBagConstraints.CENTER,GridBagConstraints.NONE,new Insets(10,0,10,0),0,0);     gridbag.setConstraints(jbutton2, constraints);     jpanel.add(jbutton2);          //添加画板到窗体     jframe.add(jpanel);     //窗体初始化完成   }      private static GridBagConstraints getGridBagConstraints(int gridx,int gridy,int gridwidth,int gridheight,double weightx,double weighty,int anchor,int fill,Insets insets,int ipadx,int ipady){      return new GridBagConstraints(gridx, gridy, gridwidth, gridheight, weightx, weighty, anchor, fill, insets, ipadx, ipady);    }      public static void main(String[] args) {      new GUIT();      jframe.setVisible(true);    } }