我写的这个数据库程序，在程序中添加的客户基本信息，没运行一次程序都增加一次，这是为什么啊？？
就是每运行一次程序都添加一次 张三 李四 王五的信息，三个三个的添加，我修改一个客户的信息是也是他们三个一起修改，就是三个三个的修改，改一个变三个，是不是我添加数据库信息的位置不对啊？大家给我挑挑毛病吧。

源程序1：
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class Database {

  public static Connection cn;
  public static Statement st;
  public static ResultSet rs;
   

  public static boolean joinDB() {
  boolean joinFlag;
  try {
  joinFlag = true;
  Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
  cn = DriverManager.getConnection("jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=sample","sa","605");
   
  cn.setCatalog("sample");
  System.out.println("数据库连接成功");
  st = cn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
  ResultSet.CONCUR_READ_ONLY);
  st.execute("INSERT INTO Table3 VALUES ('admin','123')");
  st.execute("INSERT INTO Clientm VALUES ('张三','男','23')");
  st.execute("INSERT INTO Clientm VALUES ('李四','女','25')");
  st.execute("INSERT INTO Clientm VALUES ('王五','男','20')");
   
  return joinFlag;

  } catch (SQLException sqlEx) {
  System.out.println(sqlEx.getMessage());

  joinFlag = false;
  return joinFlag;

  } catch (ClassNotFoundException notfoundEX) {
  System.out.println(notfoundEX.getMessage());

  joinFlag = false;
  return joinFlag;
  }
  }

  public static boolean executeSQL(String sqlString) {
  boolean executeFlag;
  try {
  st.execute(sqlString);
  executeFlag = true;
  } catch (Exception e) {
  executeFlag = false;
  System.out.println("sql exception:" + e.getMessage());
  }
  return executeFlag;
  }


  public static boolean query(String sqlString) {

  try {
  rs = null;
   
  rs = st.executeQuery(sqlString);
  } catch (Exception Ex) {
  System.out.println("sql exception:" + Ex);
  return false;
  }
  return true;
  }
}


源程序2：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.sql.*;
import javax.swing.*;
public class Land
{
public static void main(String[] args)
{
LandFrame frame=new LandFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}




class LandFrame extends JFrame
{
JFrame jf ;
JLabel labelWelcome = new JLabel("小区车辆管理系统");
JLabel labelName=new JLabel("用户名：");
JLabel labelPassword=new JLabel("密码：");
JTextField textName=new JTextField();
JPasswordField textPassword=new JPasswordField();
JButton buttonEnter=new JButton("登录");
JButton buttoncancel=new JButton("清空");

public LandFrame()
{
jf=this;
Toolkit kit=Toolkit.getDefaultToolkit();
Dimension screenSize=kit.getScreenSize();