在Java中检查字符串中的字母大小写（大写/小写）

Question

我遇到的问题是我无法让我的密码验证程序来检查字符串，以确保其中的一个字符为大写字母，而一个字符为小写字母，它将检查整个字符串中是否存在一个字符。其他，并根据要检查的语句打印错误消息。

我已经查看了该站点和Internet上的答案，但是找不到。这是功课。

下面是我当前的代码。

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();
            }
        }
    }
}

Answer 1

要确定字符串是否包含大写和小写字符，可以使用以下命令：

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

这使您可以检查：

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

本质上，这通过检查String是否等于其全部小写字母或等效的大写字母而起作用。如果不正确，则必须至少有一个大写或小写字符。

至于您的其他条件，可以通过类似的方式满足这些条件：

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

带有上述适当的错误消息。