一个神奇的现象，我左边JTree，右边JTable，都加了JScrollPane,用JSplitPane分左右，JTable读数据库，但是必须先移动一下JTree和JTable分解的那条东西

未移动前
移动后
谁知道原因吗，附源码
import javax.swing.*;
import javax.swing.tree.*;
import javax.swing.event.*;
import java.awt.event.*;
import java.awt.*;
import java.io.*;
import java.util.*;
import javax.swing.table.DefaultTableModel;
import java.sql.*;public class Test3 extends JFrame implements TreeSelectionListener{
private JScrollPane jsp_tree,jsp_table;
private JTree tree;
private JTable tb;
Connection conn;
ResultSet res;
  Statement sta; 
Object name[] = {"年份","学院","专业代码","专业","总分","英语","数学"};
Object info[][];
String academy,subject;
int year,code,total,en,math;

public Test3(){
super("研究生录取信息查询系统");
info = new Object[50][7];
Container c = getContentPane();
//定义根节点
DefaultMutableTreeNode root = new DefaultMutableTreeNode("区域选择");
//定义树叶节点
DefaultMutableTreeNode node_e = new DefaultMutableTreeNode("华东");
DefaultMutableTreeNode node_s = new DefaultMutableTreeNode("华南");
DefaultMutableTreeNode node_n = new DefaultMutableTreeNode("华北");
DefaultMutableTreeNode node_c = new DefaultMutableTreeNode("华中");
root.add(node_e);
root.add(node_s);
root.add(node_n);
root.add(node_c);

DefaultMutableTreeNode leafnode1 = new DefaultMutableTreeNode("上海交通大学");
node_e.add(leafnode1);
DefaultMutableTreeNode leafnode2 = new DefaultMutableTreeNode("厦门大学");
node_e.add(leafnode2);
DefaultMutableTreeNode leafnode3 = new DefaultMutableTreeNode("复旦大学");
node_e.add(leafnode3);


DefaultMutableTreeNode leafnode4 = new DefaultMutableTreeNode("中山大学");
node_s.add(leafnode4);
DefaultMutableTreeNode leafnode5 = new DefaultMutableTreeNode("深圳大学");
node_s.add(leafnode5);
DefaultMutableTreeNode leafnode6 = new DefaultMutableTreeNode("广西大学");
node_s.add(leafnode6);


DefaultMutableTreeNode leafnode7 = new DefaultMutableTreeNode("东北大学");
node_n.add(leafnode7);
DefaultMutableTreeNode leafnode8 = new DefaultMutableTreeNode("东北财经大学");
node_n.add(leafnode8);
DefaultMutableTreeNode leafnode9 = new DefaultMutableTreeNode("哈尔滨工业大学");
node_n.add(leafnode9);


DefaultMutableTreeNode leafnode_10 = new DefaultMutableTreeNode("武汉大学");
node_c.add(leafnode_10);
DefaultMutableTreeNode leafnode_11 = new DefaultMutableTreeNode("华中科技大学");
node_c.add(leafnode_11);
DefaultMutableTreeNode leafnode_12 = new DefaultMutableTreeNode("中南财经政法大学");
node_c.add(leafnode_12);

tree = new  JTree(root);
tree.getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);//只能选一个结点

tb = new JTable(info,name);
jsp_tree = new JScrollPane(tree);
jsp_table = new JScrollPane(tb);
JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,true,jsp_tree,jsp_table);
tree.addTreeSelectionListener(this);    //监听器
c.add(splitPane);
pack();
setSize(800,600);
setVisible(true);

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

public void valueChanged(TreeSelectionEvent e){
if(e.getSource() == tree){
DefaultMutableTreeNode selectionNode = (DefaultMutableTreeNode)tree.getLastSelectedPathComponent();
if(selectionNode.isLeaf()){
String nodeName = selectionNode.toString();
if(nodeName.equals("中南财经政法大学")){zncj();}
}
}
}

private void zncj(){
int i = 0;
try{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
}
catch(ClassNotFoundException ce){
System.out.println("SQLException:" + ce.getMessage());
}

try{
conn = DriverManager.getConnection("jdbc:odbc:mydb","","");
sta = conn.createStatement();
res = sta.executeQuery("select * from zncjzf");
while(res.next()){
year = res.getInt("年份");
academy = res.getString(2);
code = res.getInt("专业代码");
subject = res.getString(4);
total = res.getInt("总分");
en = res.getInt("英语");
math = res.getInt("数学");
info[i][0] = String.valueOf(year);
info[i][1] = academy;
info[i][2] = String.valueOf(code);
info[i][3] = subject;
info[i][4] = String.valueOf(total);
info[i][5] = String.valueOf(en);
info[i][6] = String.valueOf(math);
i++;
}
conn.close();
}
catch(SQLException be){
System.out.println("SQLException:" + be.getMessage());
}
}



public static void main(String args[]){
new Test3();
}
}