JAVA实现用户注册，登录，修改密码

class

import java.util.Arrays;
import java.util.Scanner;

public class User {
    String name;
    String password;
    String sex ;
    int age ;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    
    public User[] shuzu(User[] users) {  //初始化数组，预存2人
        users[0].name = "qqq";
        users[0].password = "123";
        users[1].name = "bbb";
        users[1].password = "456";
    for (int i = 0; i < users.length; i++) {
        System.out.println(users[i].name+" "+users[i].password);
    }
        return users;
    }
//______________________注册__________________________________    
    public User[] register(String newn,String newp,User[] users){
        users= Arrays.copyOf(users, users.length+1);//数组扩容+1
        User q = new User() ;
//        System.out.println(users.length); //输出新数组长度，辅助校验数组扩容
        int a = 0 ;
        for (int i = 0; i < users.length-1; i++) { //校验用户名是否重复，重复 a+1
            if(users[i].name.equals(newn) ){
                a++;
            }
        }
            if(a == 0){//a=0.用户名不重复，赋值
                users[users.length-1] = q ;//新建对象存入数组最后一个位置
                users[users.length-1].name = newn;
                users[users.length-1].password = newp;
                System.out.println("注册成功");
            }else{ // 用户名重复，提示
                System.out.println("用户名重复");
            }
//        for (int i = 0; i < users.length; i++) { //输出现有用户名，辅助校验
//        System.out.println(users[i].name);
//        }    
            return users;//返回数组
    }
//______________________登录__________________________________
    int flag;// 辅助循环判定
    public void login(String newn,String newp,User[] users){
        for (int i = 0; i < users.length; i++) {//循环遍历数组
            System.out.println(users[i].name+"标记"+i+"标记"+users[i].password);//遍历输出现在数组
            if(newn.equals(users[i].name) && newp.equals(users[i].password) ){
                flag = 0; //同一下标的对象的用户名和密码与输入的用户名和密码都一样，flag赋值0
                break;//退出循环
            }else{
                flag =1;//同一下标的对象的用户名和密码与输入的用户名和密码不一样，flag赋值0，说明输入的用户名和密码有问题
            }
        }
//        System.out.println(newn + newp);
        if(flag == 0){  // 给出系统提示
            System.out.println("登录成功");
        }else{
            System.out.println("用户名或密码错误，登录失败");
        }
    }
//________________________________修改密码——————————————————————————————————
    public User[] change(String oldn,String oldm,User[] users) {
        int a = 0 ;
        for (int i = 0; i < users.length; i++) {//循环遍历数组，校验输入的用户名是否存在
            if(oldn.equals(users[i].name)){
                a = i;
                flag = 0;
            }else{
                flag = 1 ;
            }
        }
        if(flag == 0){//输入的用户名存在，输入的新密码替换旧密码
            users[a].password = oldm;
            System.out.println("密码修改成功");
            System.out.println("用户名："+users[a].name +"   "+"新密码"+users[a].password);
        }else{//输入的用户名不存在，提示输入有误
            System.out.println("输入的用户名未查询到");
        }
        return users;//返回新数组
    }    

}    

demo

import java.util.Arrays;
import java.util.Scanner;

public class Demo1{//_____________________用户名密码————————————————————    
    public static void main(String[] args) {
    User us = new User();
    User us1 = new User();
    User us2 = new User();
    User[] users = {us1,us2};
    us.shuzu( users);//初始化数组
    for (int i = 1; i > 0; i++) {     //循环实现登录注册    
        System.out.println("请选择操作：1注册，2登录    3修改密码");
        Scanner sc = new Scanner(System.in);
        String num = sc.next();
            if(num.equals("1")){   // 注册功能
                System.out.println("_________注册__________");
                System.out.println("请创建用户名");
                us.setName(sc.next());
                System.out.println("请创建密码");
                us.setPassword(sc.next());
        //        System.out.println(us.getName());
                users = us.register(us.getName(),us.getPassword(), users);     
            }else if(num.equals("2")){ // 登录功能
                System.out.println("__________登录_________");
                System.out.println("请输入用户名");
                String newn = sc.next();
                System.out.println("请输入密码");
                String newp = sc.next();
                us.login(newn, newp, users);
            }else if(num.equals("3")){ //修改密码
                System.out.println("__________修改密码_________");
                System.out.println("请输入旧用户名");
                us.setName(sc.next());
                System.out.println("请输入新的密码");
                us.setPassword(sc.next());
                users = us.change(us.getName(), us.getPassword(), users);
            }
            else{   //输入值有误，提示
                System.out.println("输入的值有误");
            }
        }
    }
}