200分求一个打印的例子我老也做不对（再线等待）

Question

import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.border.EmptyBorder;
import javax.swing.tree.TreeModel;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;
import java.awt.*;public class TreeImage extends JFrame {
    DefaultTreeModel model;
    JTree tree;    public TreeImage() {
        super("");
        setSize(300, 200);
        model = createModel();
        tree = new JTree(model);
        tree.setCellRenderer(new MyTree());
        JScrollPane jsp = new JScrollPane(tree);
        getContentPane().add(jsp, BorderLayout.CENTER);
        setVisible(true);
    }    public DefaultTreeModel createModel() {
        DefaultMutableTreeNode root = new DefaultMutableTreeNode("a");
        DefaultMutableTreeNode b = new DefaultMutableTreeNode("b");
        DefaultMutableTreeNode c = new DefaultMutableTreeNode("c");
        root.add(b);
        root.add(c);
        return new DefaultTreeModel(root);
    }    public static void main(String args[]) {
        TreeImage ti = new TreeImage();
    }
}class MyTree extends DefaultTreeCellRenderer {
    Border border = new EmptyBorder(1, 1, 1, 1);    public MyTree() {
//        setOpaque(true);
//        setBorder(border);
    }    public Component getTreeCellRendererComponent(JTree tree, Object value,
                                                  boolean sel,
                                                  boolean expanded,
                                                  boolean leaf, int row,
                                                  boolean hasFocus) {        super.getTreeCellRendererComponent(tree,value,sel,expanded,leaf,row,hasFocus);        setText(value.toString());
        if (sel)
            setForeground(getTextSelectionColor());
        else
            setForeground(getTextNonSelectionColor());
        DefaultMutableTreeNode node = (DefaultMutableTreeNode) value;
        String str = value.toString();
        if (str == "a") {
            this.setIcon(new ImageIcon("Add.gif"));
        }
        if (str == "b") {
            this.setIcon(new ImageIcon("Copy.gif"));
        }
        if (str == "c") {
            this.setIcon(new ImageIcon("Delete.gif"));
        }
        return this;
    }
}