Question

我正在开发一个类似于数字时间机器的Java项目，它基本上可以保存特定状态的内容，将其存档到特定文件，并将其存储在某个目录中，以便安全保存。现在我正在研究密码功能。我有基础知识来检查它是对还是错，但当我输入错误答案时，课程在说“无效密码”后结束。有没有办法让它从else语句的末尾循环到main的开头，所以我不必每次都重新执行该类？

import java.util.Scanner;
import java.util.*;

public class Adam {

    public static void main(String args[]) {

        String passwrd = "password";
        String inputPassword;

        System.out.print("Please Input Password ");
        Scanner sc = new Scanner(System.in);
        inputPassword = sc.nextLine();

        if (inputPassword.equals(passwrd)) {
            System.out.println("Password Accepted, Loading Archive...");
        } else {
            System.out.println("Invalid Password");
        }
    }
}

Answer 1

你可以使用do while循环，如果用户输入无效，则不要继续循环。

import java.util.Scanner;
import java.util.*;

public class Adam {

    public static void main(String args[]) {
        String passwrd = "password";

        String inputPassword;
        boolean b = true;
        Scanner sc = new Scanner(System.in);
        do {

            System.out.print("Please Input Password ");

            inputPassword = sc.nextLine();

            if (inputPassword.equals(passwrd)) {

                System.out.println("Password Accepted, Loading Archive...");
                b = false;
            } else {

                System.out.println("Invalid Password");
                b = true;

            }

        } while (b);

    }
}

DEMO

Answer 2

每当您想运行某些代码时，请检查结果，然后在必要时重复最明显的结构do while。

如下所示：

String inputPassword = null;
do {
    if (inputPassword != null)
        System.out.println("Invalid password");
     System.out.println("Enter password");
     inputPassword = sc.nextLine();
} while (!inputPassword.equals(password));

Answer 3

只需将整个代码放入while（true）循环中，如果密码为walid，则会中断

public static void main(String args[]) 
{
    String passwrd = "password";
    String inputPassword;

    while(true)
    {    
        System.out.print("Please Input Password ");
        Scanner sc = new Scanner(System.in);
        inputPassword = sc.nextLine();

        if (inputPassword.equals(passwrd)) 
        {
            System.out.println("Password Accepted, Loading Archive...");
            break; //here you are getting out of loop
        } 
        else 
        {
            System.out.println("Invalid Password");
            //you are not breaking loop so the program will return to the beggining
        }
    }
}

Answer 4

    public static void main(String args[]) {
       String password = "password";
       String inputPassword;

        while(inputPassword == null || !inputPassword.equals(password)){
           System.out.print("Please Input Password ");
           Scanner sc = new Scanner(System.in);
           inputPassword = sc.nextLine();

           if (!inputPassword.equals(password)) {
               System.out.println("Invalid Password");
           } 
       }
       System.out.println("Password Accepted, Loading Archive...");
    }

Answer 5

尝试输入密码的次数有限，这是一个好主意。例如，要尝试输入三次密码，您将拥有以下代码：

Scanner sc = new Scanner(System.in);
for (i = 0; i < 4; ++i) {
    System.out.print("Please Input Password ");
    inputPassword = sc.nextLine();

    if (inputPassword.equals(passwrd)) {
        System.out.println("Password Accepted, Loading Archive...");
        break;
    } 
    else {
        System.out.println("Invalid Password");
    }
}

Answer 6

我在程序中添加了一个while循环和一个标志。请看一下：

public static void main(String[] args) {
        String passwrd = "password";

        boolean wrongPassword = true;

        while(wrongPassword){

            String inputPassword;

            System.out.print("Please Input Password ");
            Scanner sc = new Scanner(System.in);
            inputPassword = sc.nextLine();

            if (inputPassword.equals(passwrd)) {

                System.out.println("Password Accepted, Loading Archive...");
                wrongPassword = false;

            } 
            else {
                System.out.println("Invalid Password");
            }
        }

    }

Answer 7

使用do-while循环：

String passwrd = "password";
String inputPassword ="";
Scanner sc = new Scanner(System.in);

 do{
    System.out.print("Please Input Password ");
   // get the password from user
    inputPassword = sc.nextLine();

    // if password matches print success and break out of loop
    if (inputPassword.equals(passwrd)) {
       System.out.println("Password Accepted, Loading Archive...");
       break;
    } 
    else{
       System.out.println("Invalid Password");
     }

   }while(true);

Answer 8

使用do-while循环。此外，您的代码存在一些安全问题：

不要将System.in用于密码。请改用Console。（但是，如果从IDE运行程序，则可能没有控制台。在这种情况下，请改用GUI方法。）
输入密码后直接隐藏密码。

输入后尽快清除密码缓冲区（即覆盖密码缓冲区）。请参阅Console文档。

Console con = System.console();
if (con == null)
    throw new IOException("This JVM has no console");

boolean pwdCorrect;
do {
    char[] inputPassword = con.readPassword("Please input password: ");
    String hashedInputPassword = hashPassword(inputPassword);  // search Internet for how to hash a password
    for (int i = 0; i < inputPassword.length; i++)
        inputPassword[i] = '\0';
    pwdCorrect = isValidPassword(hashedInputPassword);  // e.g. by looking it up in a password file
    if (pwdCorrect)
        System.out.println("Password accepted. Loading archive...");
    else
        System.out.println("Invalid password.");
} while (!pwdCorrect);

从特定点循环到Java中的另一个点？

8 个答案: