实现注册的账户在重新运行程序后依然可以登录

package com.test2;

import java.io.Serializable;
/**
 * 用户类
 * @author jjit
 *
 */
public class User implements Serializable{
    private String name;
    private int id;
    private String password;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public User(String name, int id, String password) {
        super();
        this.name = name;
        this.id = id;
        this.password = password;
    }
    public User() {
        super();
    }
    public String toString() {
        return "User [name=" + name + ", id=" + id + ", password=" + password + "]";
    }
    
}

package com.test2;
/**
 * IO对象的输入输出
 */
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class UserIO {
    public static void ObjectOutputStream(User user) {
        //序列化
        java.io.ObjectOutputStream oos = null;
        FileOutputStream fos = null;
        
        try {
            fos = new FileOutputStream(user.getId()+".txt");
            oos = new java.io.ObjectOutputStream(fos);
            
            oos.writeObject(user);
            oos.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                oos.close();
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    public static User ObjectInputStream(User user1) {
        //反序列化
        java.io.ObjectInputStream ois = null;
        FileInputStream fis = null;
        
        try {
            fis = new FileInputStream(user1.getId()+".txt");
            ois = new java.io.ObjectInputStream(fis);
            User u = (User)ois.readObject();
            if(u!=null) {
                return u;
            }
        } catch (FileNotFoundException e) {
//            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } finally {
            try {
                if(ois!=null) {
                    ois.close();
                    
                }
                if(fis != null) {
                    fis.close();
                }
                
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}

package com.test2;
/**
 * 实现类
 */
import java.util.Scanner;

public class Master {
    public void print() {
        Scanner sc = new Scanner(System.in);
        User user = new User();
        while(true) {
            System.out.println("1.注册	2.登录	3.退出");
            int choose = sc.nextInt();
            switch (choose) {
            case 1:
                System.out.println("请输入用户名：");
                user.setName(sc.next());
                System.out.println("请输入用户账号：");
                user.setId(sc.nextInt());
                System.out.println("请输入账号密码：");
                user.setPassword(sc.next());
                UserIO.ObjectOutputStream(user);
                System.out.println("注册成功");
                continue;
            case 2:
                
                System.out.println("请输入用户账号：");
                int a = sc.nextInt();
                System.out.println("请输入账号密码：");
                String b = sc.next();
                User user1 = new User(null,a,b);
                User user2 =UserIO.ObjectInputStream(user1);
                if(user2 == null) {
                    System.out.println("登录失败");
                }else if(user2.getId() == user1.getId()&&user2.getPassword().equals(user1.getPassword())) {
                    System.out.println("登录成功");
                }else {
                    System.out.println("密码或账号错误！");
                }
                break;
            case 3:
                System.out.println("退出成功");
                break;

            default:
                break;
            }
        }
    }
}

package com.test2;
/**
 * 测试类
 * @author jjit
 *
 */
public class Main {
    public static void main(String[] args) {
        Master mt = new Master();
        mt.print();
    }
}