如何检查 Java 字符串是否至少包含一个大写字母、小写字母和数字？

Question

I know that I could do this with a series of for loops that iterate through the string but that would be terrible programming. Well, my professor prefers I don't do it this way. I'd like to use regular expressions to do this.

Answer 1

For a simple string check, a single sweep through the string is enough. Since Regex will not offer any significant benefit, here is a simple for loop to achieve the same :

private static boolean checkString(String str) {
    char ch;
    boolean capitalFlag = false;
    boolean lowerCaseFlag = false;
    boolean numberFlag = false;
    for(int i=0;i < str.length();i++) {
        ch = str.charAt(i);
        if( Character.isDigit(ch)) {
            numberFlag = true;
        }
        else if (Character.isUpperCase(ch)) {
            capitalFlag = true;
        } else if (Character.isLowerCase(ch)) {
            lowerCaseFlag = true;
        }
        if(numberFlag && capitalFlag && lowerCaseFlag)
            return true;
    }
    return false;
}

Test run:

System.out.println(checkString("aBCd1")); // output is true
System.out.println(checkString("abcd")); //output is false

I think this should help OP's particular problem.

Answer 2

Example of @goshDeveloper's answer.

First create a Pattern variable with regular expression you want.

public final Pattern textPattern = Pattern.compile("^(?=.*[a-z])(?=.*[A-Z])(?=.*\\d).+$");

Second you can use it like this:

public boolean isTextValid(String textToCheck) {
return textPattern.matcher(textToCheck).matches();
}

Answer 3

Using Java 9:

public boolean isValid(String value) {
    return containsLowerCase(value) && 
           containsUpperCase(value) && 
           containsNumber(value);
}

private boolean containsLowerCase(String value) {
    return contains(value, i -> Character.isLetter(i) && Character.isLowerCase(i));
}

private boolean containsUpperCase(String value) {
    return contains(value, i -> Character.isLetter(i) && Character.isUpperCase(i));
}

private boolean containsNumber(String value) {
    return contains(value, Character::isDigit);
}

private boolean contains(String value, IntPredicate predicate) {
    return value.chars().anyMatch(predicate);
}

Answer 4

Try regular expression

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).+$

descriptions are as follow
(?=.*[a-z])  -- check lower case letter
(?=.*[A-Z]) -- check upper case letter
(?=.*\d) -- check one digit exists

Answer 5

you can use :

public static boolean isTextContainUpperCase(String text) {
       if (StringUtils.isEmpty(text)) {
              return false;
       }
       return !text.equals(text.toLowerCase());
}

Answer 6

If you are looking to check whether your string contains uppercase letter or not, you can use below pattern:

String s="abcDe_shdgwU";    //you can have any String here

if(s.matches(".*[A-Z].*"))
   System.out.println("The String contains Uppercase letter(s)");
else
  System.out.println("does not contain Uppercase letter(s)");

Hope that helps. Thank you. Regards, Tanumay Saha

Answer 7

You can use Character class of java. So for lowercase, Character.isLowerCase(ch) Character.isUpperCase(ch) . For this you have to iterate over the string . I know that bit is irrelevant to you, however you can use "\\d+" for numbers in a string.

Answer 8

final String toCheck = "hasUppercasechar";
final boolean checkOk = !toCheck.chars().filter(Character::isUpperCase).findAny().isEmpty()

take a look at java.lang.Character and combine the checks you need

Answer 9

See the code below;
public class passwordValidationOne {
    public static void main(String[] args) {
        String pass = "Password1";
        System.out.println(valPassword(pass));
    }
    public static boolean valPassword(String password){
        if (password.length()>7){
            if (checkPass(password)){
                return true;
            }
            else {
                return false;
            }
        }
        else{
            System.out.println("Too Small");
            return false;
        }
    }
    public static boolean checkPass(String password){
        boolean hasNum =false; //check if password has a number
        boolean hasCap =false; //check if password has uppercase character
        boolean hasLow =false; //check if password has lowercase characters
        char c; // used to check every single character in the password

        //loop for every single character in a string
        for (int i =0; i<password.length(); i++ ){
            //assign c to the character we are looking for
            c = password.charAt(i);
            if (Character.isDigit(c)){
                hasNum = true;
            } else if (Character.isUpperCase(c)) {
                hasCap = true;
            } else if (Character.isLowerCase(c)) {
                hasLow = true;
            }
            // check if all the three boolean variables are true
            if (hasNum && hasCap && hasLow){
                return true;
            }
        }
       return  false;

    }
}