swing中Tree与滚动条用法实例分析

import java.awt.*;import java.awt.event.*;import javax.swing.*;import javax.swing.tree.*;public class test extends JApplet{  JTree tree;  JTextField jtf;  public void init(){    Container contentPane = getContentPane();    contentPane.setLayout(new BorderLayout());    DefaultMutableTreeNode top = new DefaultMutableTreeNode("Options");    DefaultMutableTreeNode a = new DefaultMutableTreeNode("A");    top.add(a);    DefaultMutableTreeNode a1 = new DefaultMutableTreeNode("A1");    a.add(a1);    DefaultMutableTreeNode a2 = new DefaultMutableTreeNode("A2");    a.add(a2);    DefaultMutableTreeNode b = new DefaultMutableTreeNode("B");    top.add(b);    DefaultMutableTreeNode b1 = new DefaultMutableTreeNode("B1");    b.add(b1);    DefaultMutableTreeNode b2 = new DefaultMutableTreeNode("B2");    b.add(b2);    tree = new JTree(top);    int v = ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED;    int h = ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED;    JScrollPane jsp = new JScrollPane(tree,v,h);    contentPane.add(jsp, BorderLayout.CENTER);    jtf = new JTextField("", 20);    contentPane.add(jtf, BorderLayout.SOUTH);    tree.addMouseListener(new MouseAdapter(){      public void mouseClicked(MouseEvent me){        doMouseclicked(me);      }    });  }  void doMouseclicked(MouseEvent me){    TreePath tp = tree.getPathForLocation(me.getX(), me.getY());    if(tp !=null)      jtf.setText(tp.toString());    else      jtf.setText("");  }}