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10-4:以TreeModel构造JTree.

除了以节点的观念(TreeNode)建立树之外，你可以用data model的模式建立树。树的data model称为TreeModel,用此模式的好处 是可以触发相关的树事件，来处理树可能产生的一些变动。TreeModel是一个interface,里面定义了8种方法;如果你是一个喜欢自己 动手做的人，或是你想显示的数据格式很复杂，你可以考虑直接实作TreeModel界面中所定义的方法来构造出JTree.TreeModel界面 的方法如下所示:

TreeModel方法:

• void addTreeModelListener(TreeModelListener l):增加一个TreeModelListener来监控TreeModelEvent事件。
• Object getChild(Object parent,int index):返回子节点。
• int getChildCount(Object parent):返回子节点数量.
• int getIndexOfChild(Object parent,Object child):返回子节点的索引值。
• Object getRoot():返回根节点。 boolean isLeaf(Object node):判断是否为树叶节点。
• void removeTreeModelListener(TreeModelListener l):删除TreeModelListener。
• void valueForPathChanged(TreePath path,Object newValue):当用户改变Tree上的值时如何应对。

你可以实作出这8种方法，然后构造出自己想要的JTree,不过在大部份的情况下我们通常不会这样做，毕竟要实作出这8种方法不 是件很轻松的事，而且java本身也提供了一个默认模式，叫做DefaultTreeModel,这个类已经实作了TreeModel界面，也另外提供许 多实用的方法。利用这个默认模式，我们便能很方便的构造出JTree出来了。下面为DefaultTreeModel的构造函数与范例:

DefaultTreeModel构造函数:

• DefaultTreeModel(TreeNode root):建立DefaultTreeModel对象，并定出根节点。
• DefaultTreeModel(TreeNode root,Boolean asksAllowsChildren):建立具有根节点的DefaultTreeModel对象，并决定此节点是否允 许具有子节点。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.tree.*;
import com.incors.plaf.alloy.*;//组件的下载网址http://www.incors.com/lookandfeel/

/*将alloy.jar放在c:\j2sdk1.4.0\jre\lib\ext\目录下.
 */
public class TreeDemo3 {
	public TreeDemo3() {
		JFrame f = new JFrame("TreeDemo");
		Container contentPane = f.getContentPane();

		DefaultMutableTreeNode root = new DefaultMutableTreeNode("资源管理器");
		DefaultMutableTreeNode node1 = new DefaultMutableTreeNode("我的公文包");
		DefaultMutableTreeNode node2 = new DefaultMutableTreeNode("我的电脑");
		DefaultMutableTreeNode node3 = new DefaultMutableTreeNode("收藏夹");
		DefaultMutableTreeNode node4 = new DefaultMutableTreeNode("Readme");

		DefaultTreeModel treeModel = new DefaultTreeModel(root);

		/*
		 * DefaultTreeModel类所提供的insertNodeInto()方法加入节点到父节点的数量.
		 * 利用DefaultMutableTreeNode类所提供的getChildCount()方法取得目前子节点的数量.
		 */
		treeModel.insertNodeInto(node1, root, root.getChildCount());
		treeModel.insertNodeInto(node2, root, root.getChildCount());
		treeModel.insertNodeInto(node3, root, root.getChildCount());
		treeModel.insertNodeInto(node4, root, root.getChildCount());

		DefaultMutableTreeNode leafnode = new DefaultMutableTreeNode("公司文件");

		// DefaultTreeModel类所提供的insertNodeInto()方法加入节点到父节点的数量.
		treeModel.insertNodeInto(leafnode, node1, node1.getChildCount());
		leafnode = new DefaultMutableTreeNode("个人信件");
		treeModel.insertNodeInto(leafnode, node1, node1.getChildCount());
		leafnode = new DefaultMutableTreeNode("私人文件");
		treeModel.insertNodeInto(leafnode, node1, node1.getChildCount());

		leafnode = new DefaultMutableTreeNode("本机磁盘(C:)");
		treeModel.insertNodeInto(leafnode, node2, node2.getChildCount());
		leafnode = new DefaultMutableTreeNode("本机磁盘(D:)");
		treeModel.insertNodeInto(leafnode, node2, node2.getChildCount());
		leafnode = new DefaultMutableTreeNode("本机磁盘(E:)");
		treeModel.insertNodeInto(leafnode, node2, node2.getChildCount());

		DefaultMutableTreeNode node31 = new DefaultMutableTreeNode("网站列表");
		treeModel.insertNodeInto(node31, node3, node3.getChildCount());
		leafnode = new DefaultMutableTreeNode("奇摩站");
		treeModel.insertNodeInto(leafnode, node3, node3.getChildCount());
		leafnode = new DefaultMutableTreeNode("职棒消息");
		treeModel.insertNodeInto(leafnode, node3, node3.getChildCount());
		leafnode = new DefaultMutableTreeNode("网络书店");
		treeModel.insertNodeInto(leafnode, node3, node3.getChildCount());
		try {
			LookAndFeel alloyLnF = new AlloyLookAndFeel();
			UIManager.setLookAndFeel(alloyLnF);
		} catch (UnsupportedLookAndFeelException ex) {
			// You may handle the exception here
		}
		// this line needs to be implemented in order to make JWS work properly
		UIManager.getLookAndFeelDefaults().put("ClassLoader",
				getClass().getClassLoader());

		// 以TreeModel建立JTree。
		JTree tree = new JTree(treeModel);
		/* 改变JTree的外观* */
		tree.putClientProperty("JTree.lineStyle", "Horizontal");
		/* 改变JTree的外观* */
		JScrollPane scrollPane = new JScrollPane();
		scrollPane.setViewportView(tree);

		contentPane.add(scrollPane);
		f.pack();
		f.setVisible(true);

		f.addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent e) {
				System.exit(0);
			}
		});

	}

	public static void main(String args[]) {

		new TreeDemo3();
	}
}