关于循环与再次循环的问题。

Question

import java.util.Scanner;public class  Test2
{
    public static void main(String[] args)
    {
            String username="admin";
            String password="admin";
            System.out.println("\t\t\t欢迎光临我的系统\n");
            System.out.println("\t\t\t\t1.登录系统\n");
            System.out.println("\t\t\t\t2.退出");
            System.out.println("*******************************************************************************************************************************************************\n");
                System.out.println("请选择，输入数字：");
                Scanner input=new Scanner(System.in);
                int num =input.nextInt();
                switch(num){
                case 1:
                        System.out.println("请输入用户名：");
                        String name=input.next();
                        System.out.println("请输入密码：");
                        String pass=input.next();
                        if(name.equals(username)&&pass.equals(password)){
                            System.out.println("进入系统");
                        }else{
                            System.out.println("输入有误，你无权进入系统，请重新输入数字");   
                            //？当执行到这边的时候想办法在让他重新在输入数字在执行
                        }
                        break;
                case 2:
                        System.out.println("谢谢你的使用。");
                        break;
                default:
                    System.out.println("输入有误，请重新输入数字");
                    //？当执行到这边的时候想办法在让他重新在输入数字在执行
                }
        }
    }
这中间的两个注释不知道该怎么写再次循环的问题，求大神帮忙想想。？

Answer 1

 public static void main(String[] args)
    {
            String username="admin";
            String password="admin";
            System.out.println("\t\t\t欢迎光临我的系统\n");
            System.out.println("\t\t\t\t1.登录系统\n");
            System.out.println("\t\t\t\t2.退出");
            System.out.println("*******************************************************************************************************************************************************\n");
                System.out.println("请选择，输入数字：");
                Scanner input=new Scanner(System.in);
                while(true){
                int num =input.nextInt();
                switch(num){
                case 1:
                        System.out.println("请输入用户名：");
                        String name=input.next();
                        System.out.println("请输入密码：");
                        String pass=input.next();
                        if(name.equals(username)&&pass.equals(password)){
                            System.out.println("进入系统");
                        }else{
                            System.out.println("输入有误，你无权进入系统，请重新输入数字");   
                            //？当执行到这边的时候想办法在让他重新在输入数字在执行
                        }
                        break;
                case 2:
                        System.out.println("谢谢你的使用。");
                        break;
                default:
                    System.out.println("输入有误，请重新输入数字");
                    //？当执行到这边的时候想办法在让他重新在输入数字在执行
                }
        }}使用循环 ！ 多看看书吧

Answer 2

import java.util.Scanner;public class  Test2
{
    public static void main(String[] args)
    {
            String username="admin";
            String password="admin";
            boolean con;
    do{
     con=true;
            System.out.println("\t\t\t欢迎光临我的系统\n");
            System.out.println("\t\t\t\t1.登录系统\n");
            System.out.println("\t\t\t\t2.退出");
            System.out.println("*******************************************************************************************************************************************************\n");
                System.out.println("请选择，输入数字：");
                Scanner input=new Scanner(System.in);
                int num =input.nextInt();
                switch(num){
                case 1:
                        System.out.println("请输入用户名：");
                        String name=input.next();
                        System.out.println("请输入密码：");
                        String pass=input.next();
                        if(name.equals(username)&&pass.equals(password)){
                            System.out.println("进入系统");
                        }else{
                            System.out.println("输入有误，你无权进入系统，请重新输入数字");   
                             con=false;
                        }
                        break;
                case 2:
                        System.out.println("谢谢你的使用。");
                        break;
                default:
                    System.out.println("输入有误，请重新输入数字");
                   con=false;
                }
                }while(!con);
        }
    }
用do {}while();成功解决问题