How do I check if a Java String contains at least one capital letter, lowercase letter, and number?

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

Answer 1

you can use :

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

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

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 4

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 5

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 6

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.