jtree节点图片问题

JTree用法及JTree使用经验总结
import java.awt.Dimension;
import java.awt.Color;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.BoxLayout;
import javax.swing.tree.TreePath;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
/*
JTree的构造函数:
JTree()
JTree(Hashtable value)
JTree(Object[] value)//只有这个构造函数可以创建多个根结点
JTree(TreeModel newModel)
JTree(TreeNode root)
JTree(TreeNode root, boolean asksAllowsChildren)
JTree(Vector value)

*/
public class JTreeDemo
{
public static void main (String[] args)
{

// 构造函数：JTree()
JTree example1 = new JTree();

// 构造函数：JTree(Object[] value)
Object[] letters = { " a " , " b " , " c " , " d " , " e " };