在Java中检查字符串中的字母大小写（上/下） [英] Checking letter case (Upper/Lower) within a string in Java

问题描述

我遇到的问题是我无法让我的密码验证程序检查字符串以确保其中1个字符为大写，1个为小写字母，它将检查整个字符串是否为另一个并根据它正在检查的语句打印错误消息。

The problem that I am having is that I can't get my Password Verification Program to check a string to ensure that, 1 of the characters is in upper case and one is in lower case, it will check the whole string for one of the other and print the error message based on which statement it is checking.

我查看了这个网站和互联网的答案，我无法找到一。这是作业。

I have looked over this site and the internet for an answer and I am unable to find one. This is homework.

以下是我当前的代码。

import java.util.Scanner;

public class password
{
    public static void main(String[] args)
    {
        Scanner stdIn = new Scanner(System.in);
        String password;
        String cont = "y";
        char ch;
        boolean upper = false;
        boolean lower = false;

        System.out.println("Setting up your password is easy. To view requirements enter Help.");
        System.out.print("Enter password or help: ");
        password = stdIn.next();
        ch = password.charAt(0);

        while (cont.equalsIgnoreCase("y"))
        {
            while (password.isEmpty())
            {
                System.out.print("Enter password or help: ");
                password = stdIn.next();       
            }

            if (password.equalsIgnoreCase("help"))
            {
                 System.out.println("Password must meet these requirements." +
                     "\nMust contain 8 characters.\nMust contain 1 lower case letter." +
                     "\nMust contain 1 upper case letter.\nMust contain 1 numeric digit." +
                     "\nMust contain 1 special character !@#$%^&*\nDoes not contain the word AND or NOT.");

                password = "";
            }
            else if (password.length() < 8)
            {
                System.out.println("Invalid password - Must contain 8 charaters.");
                password = "";
            }
            else if (!(Character.isLowerCase(ch)))
            {
                for (int i=1; i<password.length(); i++)
                {
                    ch = password.charAt(i);

                    if (!Character.isLowerCase(ch))
                    {  
                        System.out.println("Invalid password - Must have a Lower Case character.");
                        password = "";
                    }
                }
            }
            else if (!(Character.isUpperCase(ch)))
            {
                for (int i=0; i<password.length(); i++)
                {       
                    ch = password.charAt(i);

                    if (!Character.isUpperCase(ch))
                    {
                        System.out.println("Invalid password - Must have an Upper Case character.");
                        password = "";
                    }
                }
            }
            else
            {
                System.out.println("Your password is " + password);

                System.out.print("Would you like to change your password? Y/N: ");
                cont = stdIn.next();
                password = "";
            }

            while (!cont.equalsIgnoreCase("y") && !cont.equalsIgnoreCase("n"))
            {
                System.out.print("Invalid Answer. Please enter Y or N: ");
                cont = stdIn.next();
            }
        }
    }
}

推荐答案

要确定String是否包含大写字母和小写字母，您可以使用以下内容：

To determine if a String contains an upper case and a lower case char, you can use the following:

boolean hasUppercase = !password.equals(password.toLowerCase());
boolean hasLowercase = !password.equals(password.toUpperCase());

这可以让您检查：

if(!hasUppercase)System.out.println("Must have an uppercase Character");
if(!hasLowercase)System.out.println("Must have a lowercase Character");

本质上，这是通过检查String是否等于其完全小写或大写等效来实现的。如果不是这样，则必须至少有一个大写或小写的字符。

Essentially, this works by checking if the String is equal to its entirely lowercase, or uppercase equivalent. If this is not true, then there must be at least one character that is uppercase or lowercase.

至于其他条件，可以用类似的方式满足这些条件：

As for your other conditions, these can be satisfied in a similar way:

boolean isAtLeast8   = password.length() >= 8;//Checks for at least 8 characters
boolean hasSpecial   = !password.matches("[A-Za-z0-9 ]*");//Checks at least one char is not alpha numeric
boolean noConditions = !(password.contains("AND") || password.contains("NOT"));//Check that it doesn't contain AND or NOT

上面有适当的错误信息。

With suitable error messages as above.

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