java界面的背景图片怎么加
求帮这个图形界面加一个背景图片，最好能随着界面大小的变化而变化

Java code

import java.awt.*;import java.awt.event.*;import javax.swing.*;import javax.swing.event.*;import javax.swing.tree.*;import java.net.*;/** * 人事管理系统主界面 */public class HrMain extends JFrame implements ActionListener,TreeSelectionListener{    //框架的大小    Dimension faceSize = new Dimension(650, 450);    //程序图标    Image buaa;    //建立Jtree菜单    JTree tree;    DefaultMutableTreeNode root;  //人事管理系统    DefaultMutableTreeNode node1; //人员基本信息维护    DefaultMutableTreeNode node2; //部门信息管理    DefaultMutableTreeNode node3; //人员调动管理    DefaultMutableTreeNode node4; //人员考核管理    DefaultMutableTreeNode node5; //劳资管理    DefaultMutableTreeNode leafnode;    TreePath treePath;    //主界面面板    public static JSplitPane splitPane;    JPanel panel1;    JPanel panel2;    JPanel panel3;    JLabel welcome = new JLabel();    JScrollPane scrollPane;    /**     * 程序初始化函数     */     public HrMain() {        enableEvents(AWTEvent.WINDOW_EVENT_MASK);        //添加框架的关闭事件处理        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        this.pack();        //设置框架的大小        this.setSize(faceSize);        //设置标题        this.setTitle("人事管理系统");        //程序图标        buaa = getImage("buaa.jpg");        this.setIconImage(buaa); //设置程序图标        //设置自定义大小        this.setResizable(false);        try {                Init();        }        catch(Exception e) {            e.printStackTrace();        }    }    /**     * 程序初始化函数     */    private void Init() throws Exception {        //Container contentPane = this.getContentPane();        //contentPane.setLayout(new BorderLayout());        //添加Jtree菜单        root = new DefaultMutableTreeNode("人事管理系统");        node1 = new DefaultMutableTreeNode("基本信息管理");        node2 = new DefaultMutableTreeNode("人员调动管理");        node3 = new DefaultMutableTreeNode("人员考核管理");        node4 = new DefaultMutableTreeNode("劳资管理");        //人员基本信息        root.add(node1);        leafnode = new DefaultMutableTreeNode("添加人员信息");        node1.add(leafnode);        leafnode = new DefaultMutableTreeNode("修改人员信息");        node1.add(leafnode);        leafnode = new DefaultMutableTreeNode("删除人员信息");        node1.add(leafnode);        leafnode = new DefaultMutableTreeNode("查询人员信息");        node1.add(leafnode);        leafnode = new DefaultMutableTreeNode("部门管理");        node1.add(leafnode);        //人员调动管理        root.add(node2);        leafnode = new DefaultMutableTreeNode("人员调动");        node2.add(leafnode);        leafnode = new DefaultMutableTreeNode("调动历史查询");        node2.add(leafnode);        //人员考核管理        root.add(node3);        leafnode = new DefaultMutableTreeNode("人员考核");        node3.add(leafnode);        leafnode = new DefaultMutableTreeNode("考核历史查询");        node3.add(leafnode);        //劳资管理        root.add(node4);        leafnode = new DefaultMutableTreeNode("劳资分配管理");        node4.add(leafnode);        leafnode = new DefaultMutableTreeNode("劳资历史查询");        node4.add(leafnode);        //生成左侧的JTree        tree = new JTree(root);        scrollPane = new JScrollPane(tree);        scrollPane.setPreferredSize(new Dimension(150,400));        tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);        //生成JPanel        panel1 = new JPanel();        panel2 = new JPanel();        panel3 = new JPanel();        panel1.add(scrollPane);        welcome.setText("欢迎使用人事管理系统");        welcome.setFont(new Font("Dialog",0,16));        panel3.add(welcome);                //生成JSplitPane并设置参数        splitPane = new JSplitPane();        splitPane.setOneTouchExpandable(false);        splitPane.setContinuousLayout(true);        splitPane.setPreferredSize(new Dimension(150, 400));        splitPane.setOrientation(JSplitPane.HORIZONTAL_SPLIT);        splitPane.setLeftComponent(panel1);        splitPane.setRightComponent(panel3);        splitPane.setDividerSize(2);        splitPane.setDividerLocation(161);        //生成主界面        this.setContentPane(splitPane);        this.setVisible(true);        //添加事件侦听        tree.addTreeSelectionListener(this);        //关闭程序时的操作        this.addWindowListener(            new WindowAdapter(){                public void windowClosing(WindowEvent e){                    System.exit(0);                }            }        );    }    /**     * 事件处理     */    public void actionPerformed(ActionEvent e) {    }    /**     * JTree事件处理     */    public void valueChanged(TreeSelectionEvent tse) {        DefaultMutableTreeNode dnode =             (DefaultMutableTreeNode)tse.getPath().getLastPathComponent();        System.out.println("dnode="+dnode);        String node_str = dnode.toString();        if (node_str == "人事管理系统") {             splitPane.setRightComponent(panel3);        }        //人员基本信息管理树        else if (node_str == "基本信息管理") {             //当选中后展开或关闭叶子节点            treePath = new TreePath(node1.getPath());            if(tree.isExpanded(treePath))                tree.collapsePath(treePath);            else                tree.expandPath(treePath);        }        else if (node_str == "添加人员信息") {             Node11Panel node11Panel = new Node11Panel();            splitPane.setRightComponent(node11Panel);        }        else if (node_str == "修改人员信息") {             Node12Panel node12Panel = new Node12Panel();            splitPane.setRightComponent(node12Panel);        }        else if (node_str == "删除人员信息") {             Node13Panel node13Panel = new Node13Panel();            splitPane.setRightComponent(node13Panel);        }        else if (node_str == "查询人员信息") {             Node14Panel node14Panel = new Node14Panel();            splitPane.setRightComponent(node14Panel);        }        else if (node_str == "部门管理") {             Node15Panel node15Panel = new Node15Panel();            splitPane.setRightComponent(node15Panel);        }        //人员调动管理树        else if (node_str == "人员调动管理") {             //当选中后展开或关闭叶子节点            treePath = new TreePath(node2.getPath());            if(tree.isExpanded(treePath))                tree.collapsePath(treePath);            else                tree.expandPath(treePath);        }        else if (node_str == "人员调动") {             Node21Panel node21Panel = new Node21Panel();            splitPane.setRightComponent(node21Panel);        }        else if (node_str == "调动历史查询") {             Node22Panel node22Panel = new Node22Panel();            splitPane.setRightComponent(node22Panel);        }        //人员考核管理树        else if (node_str == "人员考核管理") {            //当选中后展开或关闭叶子节点            treePath = new TreePath(node3.getPath());            if(tree.isExpanded(treePath))                tree.collapsePath(treePath);            else                tree.expandPath(treePath);        }        else if (node_str == "人员考核") {             Node31Panel node31Panel = new Node31Panel();            splitPane.setRightComponent(node31Panel);        }        else if (node_str == "考核历史查询") {             Node32Panel node32Panel = new Node32Panel();            splitPane.setRightComponent(node32Panel);        }        //劳资管理树        else if (node_str == "劳资管理") {            //当选中后展开或关闭叶子节点            treePath = new TreePath(node4.getPath());            if(tree.isExpanded(treePath))                tree.collapsePath(treePath);            else                tree.expandPath(treePath);        }        else if (node_str == "劳资分配管理") {             Node41Panel node41Panel = new Node41Panel();            splitPane.setRightComponent(node41Panel);        }        else if (node_str == "劳资历史查询") {             Node42Panel nod42Panel = new Node42Panel();            splitPane.setRightComponent(nod42Panel);        }    }    /**     * 通过给定的文件名获得图像     */    Image getImage(String filename) {        URLClassLoader urlLoader = (URLClassLoader)this.getClass().            getClassLoader();        URL url = null;        Image image = null;        url = urlLoader.findResource(filename);        image = Toolkit.getDefaultToolkit().getImage(url);        MediaTracker mediatracker = new MediaTracker(this);        try {            mediatracker.addImage(image, 0);            mediatracker.waitForID(0);        }        catch (InterruptedException _ex) {            image = null;        }        if (mediatracker.isErrorID(0)) {            image = null;        }        return image;    }} 
 

[解决办法]
frame.setBackground(Color c);
相信 你明白了?这个只是你图片有多大,在界面中显示多大
frame.setBackground(Color.red);这个 背景红色