Java的“while”循环问题

Question

我想做的是从用户那里得到一个密码，然后检查它是否有4个条件。如果是对的话。然后打印出“密码正确”。如果不是，则向用户显示错误并返回菜单。问题是我不能回到菜单上去。如果我在第^{行执行while循环。它确实会返回，但某些“if”语句不会运行。有人能看到我被困在哪里吗？多谢各位

import java.util.Scanner;

public class Text_processing
{

    public static void main(String[] args)
    {
        Scanner kb = new Scanner(System.in);        //user input        
        String user_input;      // To hold input
        char[] array;           //Array for user_input
        int letters = 0;        // Number of letters
        int digits = 0;         // Number of digits
        boolean nu = true;      //
        boolean nl = true;
        boolean nd = true;
        boolean n7 = true;


        //User interface
        //suppose to put a while loop here, but.....
        System.out.println();
        System.out.println("Please create a password and a legal one" 
                           + " should contain the following elements:");
        System.out.println("\tAt least 7 characters in length.");
        System.out.println("\tAt least 1 upper case letter.");
        System.out.println("\tAt least 1 lower case letter.");
        System.out.println("\tAt least 1 number.");

        //Get a string from the user
        user_input = kb.nextLine();

        //Convert it to a char array
        array = user_input.toCharArray();

        for(int i = 0; i < array.length; i++)
        {
            if(!nu && !nl && !nd && !n7)
            {               
                break;
            }

            if (array.length >= 7)       //not < 7 cos breaks
            {         
                n7 = false;        
            }

            if(Character.isUpperCase(array[i]))
            {
                nu = false;             
            }

            if (Character.isLowerCase(array[i])) 
            {
                nl = false;
            }

            if (Character.isDigit(array[i])) 
            {
                nd = false;       
            }

        }

        if(n7)
        {
            System.out.println("Password does not contain 7 or more letters.");
        }
        if(nu)
        {
            System.out.println("Password does not contain an upper case letter.");
        }
        if(nl)
        {
            System.out.println("Password does not contain an lower case letter.");
        }
        if(nd)
        {
            System.out.println("Password does not contain a number.");
        }

            System.out.println("Password is correct.");


    }
}

Answer 1

我个人觉得您编写的代码太长，无法进行如此简单的检查

但问题仍然是，只有当您可以设置while循环来检查有效标志是否为true并在最后读取键盘输入时，才能修复hand

类似下面的代码：

boolean valid = false;
while (!valid) {

        for (int i = 0; i < array.length; i++) {
            valid = true;
            if (!nu && !nl && !nd && !n7) {
                break;
            }

            if (array.length >= 7) // not < 7 cos breaks
            {
                n7 = false;
            }

            if (Character.isUpperCase(array[i])) {
                nu = false;
            }

            if (Character.isLowerCase(array[i])) {
                nl = false;
            }

            if (Character.isDigit(array[i])) {
                nd = false;
            }

        }

        if (n7) {
            valid = false;
            System.out
                    .println("Password does not contain 7 or more letters.");
        }
        if (nu) {
            valid = false;
            System.out
                    .println("Password does not contain an upper case letter.");
        }
        if (nl) {
            valid = false;
            System.out
                    .println("Password does not contain an lower case letter.");
        }
        if (nd) {
            valid = false;
            System.out.println("Password does not contain a number.");
        }
        if (!valid) {
            user_input = kb.nextLine();
            array = user_input.toCharArray();
        }
    }

Answer 2

编写一个简单的方法来验证密码，如下所示

private static boolean isValid(char[] array) {
    if(array.length<7){
        return false;
    }
    else{
        boolean isUpper=false, isLower=false, isDigit=false;
        for (int i = 0; i < array.length; i++) {
            char c = array[i];
            if(Character.isUpperCase(c)){
                isUpper=true;
            }
            if(Character.isLowerCase(c)){
                isLower=true;
            }
            if(Character.isDigit(c)){
                isDigit=true;
            }
        }
        return isUpper && isLower && isDigit;
    }
}

Answer 3

while循环从以下位置开始有什么问题：

String user_input;      // To hold input

并在以下时间之前结束：

        System.out.println("Password is correct.");

Answer 4

为什么你要去的具体原因，你已经显示了内容，密码应该是什么

只需打印“密码不符合上述条件，请重试”

我觉得足够了

Answer 5

这种情况的标准模式是：

Scanner sc = new Scanner(System.in);
String userInput = null;
while (true) {
    System.out.println("please enter something:");
    userInput = sc.next();
    if (<input fails some test>) {
        System.out.println("some reason");
        continue; // try again
    }
    // repeat other tests similarly
    break; // will only get to here if input was OK
}

在输入有效输入之前，循环无法退出，在此之后userInput将保留该值

还要注意，通过将提示放在循环中，可以避免无效输入上的代码重复

Answer 6

在当前代码中，需要确保在主循环的每次迭代中重置nu、nl、nd、n7

boolean badPassword = false;
do {
    boolean nu = true;
    boolean nl = true;
    boolean nd = true;
    boolean n7 = true;
    /*
     * Add everything from your code that appears below `boolean n7 = true;`
     * and above System.out.println("Password is correct."); here...
     */

    badPassword = (n7 || nu || nl || nd);
} while (badPassword);
System.out.println("Password is correct.");