//User 用户的基本信息，也是USERINFO表中的3个列 package 登陆判断; public class User {   private String name;   private String loginname;   private String loginpsw;   public String getName() {    return name;   }   public void setName(String name) {    this.name = name;   }   public String getLoginname() {    return loginname;   }   public void setLoginname(String loginname) {    this.loginname = loginname;   }   public String getLoginpsw() {    return loginpsw;   }   public void setLoginpsw(String loginpsw) {    this.loginpsw = loginpsw;   } } //用于注册和登陆的小小代码块 package 登陆判断; import java.util.Scanner; public class In {   public static User getUser(){    User u = new User();    Scanner sc = new Scanner(System.in);    System.out.println("请输入登陆名");    u.setLoginname(sc.nextLine());    System.out.println("请输入密码");    u.setLoginpsw(sc.nextLine());    return  u;   }   public static User registerUser(){    User u = new User();    Scanner sc = new Scanner(System.in);    System.out.println("请注册用户名名");    u.setName(sc.nextLine());    System.out.println("请注册登陆名");    u.setLoginname(sc.nextLine());    System.out.println("请注册密码");    u.setLoginpsw(sc.nextLine());    return  u;   } } //登陆时的检查，判断登陆名和密码是否正确，正确则返回 用户名 package 登陆判断; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; public class Check {   public static void checkUser(User u)   {    try {     Class.forName("oracle.jdbc.driver.OracleDriver");    } catch (ClassNotFoundException e) {     e.printStackTrace();    }    String url = "jdbc:oracle:thin:@localhost:1521:orcl";    String user = "scott";    String password = "tiger";    Connection conn = null;    ResultSet rs = null;    PreparedStatement pst = null;    String sql = "Select name from USERINFO where loginname = ? and loginpsw = ? ";    try {     conn = DriverManager.getConnection(url, user, password);     pst = conn.prepareStatement(sql);     pst.setString(1, u.getLoginname());     pst.setString(2,u.getLoginpsw());     rs = pst.executeQuery();     while(rs.next()){      u.setName(rs.getString(1));     }        } catch (SQLException e) {     e.printStackTrace();    }finally{     try {      rs.close();      pst.close();      conn.close();     } catch (SQLException e) {      e.printStackTrace();     }    }    if(u.getName() == null || u.getName().isEmpty()){     System.out.println("登陆失败");    }else{     System.out.println("欢迎"+u.getName()+"登陆");    }   } } //注册界面，要判断 登陆名是否有重复，有重复则注册失败。有点小疑问，已用注释标出来 package 登陆判断; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class Register {   public static void registUser(User u){    try {     Class.forName("oracle.jdbc.driver.OracleDriver");    } catch (ClassNotFoundException e) {     e.printStackTrace();    }    String url = "jdbc:oracle:thin:@localhost:1521:orcl";    String user = "scott";    String password = "tiger";    Connection conn = null;    String sql = "Insert Into USERINFO values(?,?,?)";    PreparedStatement pst = null;    //判断登陆名是否已经存在    Statement s = null;    ResultSet rs = null;    String sql_ck = "Select LOGINNAME FROM USERINFO";    try {     conn = DriverManager.getConnection(url, user, password);     pst = conn.prepareStatement(sql);     pst.setString(1, u.getName());     pst.setString(2, u.getLoginname());     pst.setString(3, u.getLoginpsw());     //判断登陆名是否已经存在     s = conn.createStatement();     rs = s.executeQuery(sql_ck);     while(rs.next()){//为什么用 rs.getString(2)会提示 无效的索引呢      if( rs.getString("LOGINNAME").equals(u.getLoginname()) ){       System.out.println("登陆名已经存在，注册失败");       break;      }else{       pst.executeUpdate();       System.out.println("注册成功");       break;      }     }     } catch (SQLException e) {     e.printStackTrace();    }finally{     try {      rs.close();      pst.close();      s.close();      conn.close();     } catch (SQLException e) {      e.printStackTrace();     }    }       } } //main界面// //数据库中表的结构式这样 //name(用户名，用于显示), //loginname(登录名,即登陆时输入的ID) //loginpsw(登陆时输入的密码) package 登陆判断; import java.util.Scanner; public class Test {  public static void main(String[] args) {   int chos = 0;   Scanner sc = new Scanner(System.in);   System.out.println("\t\t登陆请按1\t\t注册请按2");   chos = sc.nextInt();   switch(chos){   case 1: Check.checkUser(In.getUser());break;   case 2: Register.registUser(In.registerUser());break;   default: System.out.println("请输入正确的选择");break;   }  } }