TheAlgorithms/Java · error · IllegalArgumentException

Incorrect length parameters: minLength must be <= maxLength

Error message

Incorrect length parameters: minLength must be <= maxLength and both must be > 0

What it means

Thrown by PasswordGen.generatePassword when the length constraints are invalid: minLength > maxLength, or either bound is <= 0. The generator picks a random length in [minLength, maxLength] from a fixed character set, so an inverted or non-positive range has no valid length to pick.

Source

Thrown at src/main/java/com/thealgorithms/others/PasswordGen.java:34

    private static final String LOWERCASE_LETTERS = "abcdefghijklmnopqrstuvwxyz";
    private static final String DIGITS = "0123456789";
    private static final String SPECIAL_CHARACTERS = "!@#$%^&*(){}?";
    private static final String ALL_CHARACTERS = UPPERCASE_LETTERS + LOWERCASE_LETTERS + DIGITS + SPECIAL_CHARACTERS;

    private PasswordGen() {
    }

    /**
     * Generates a random password with a length between minLength and maxLength.
     *
     * @param minLength The minimum length of the password.
     * @param maxLength The maximum length of the password.
     * @return A randomly generated password.
     * @throws IllegalArgumentException if minLength is greater than maxLength or if either is non-positive.
     */
    public static String generatePassword(int minLength, int maxLength) {
        if (minLength > maxLength || minLength <= 0 || maxLength <= 0) {
            throw new IllegalArgumentException("Incorrect length parameters: minLength must be <= maxLength and both must be > 0");
        }

        Random random = new Random();

        List<Character> letters = new ArrayList<>();
        for (char c : ALL_CHARACTERS.toCharArray()) {
            letters.add(c);
        }

        // Inbuilt method to randomly shuffle a elements of a list
        Collections.shuffle(letters);
        StringBuilder password = new StringBuilder();

        // Note that size of the password is also random
        for (int i = random.nextInt(maxLength - minLength) + minLength; i > 0; --i) {
            password.append(ALL_CHARACTERS.charAt(random.nextInt(ALL_CHARACTERS.length())));
        }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Ensure minLength <= maxLength and both are >= 1 before calling.
2. If you want a fixed-length password, pass the same value for both bounds.
3. Order/clamp the bounds from user input: min = max(1, min), max = max(min, max).
4. Validate the pair at the configuration boundary.

Example fix

// before
String pw = PasswordGen.generatePassword(12, 8); // min > max -> throws

// after
int min = Math.max(1, requestedMin);
int max = Math.max(min, requestedMax);
String pw = PasswordGen.generatePassword(min, max);

int min = Math.max(1, minLength);
int max = Math.max(min, maxLength);
String pw = PasswordGen.generatePassword(min, max);

public static boolean areValidLengths(int min, int max) {
    return min > 0 && max > 0 && min <= max;
}

try {
    pw = PasswordGen.generatePassword(minLen, maxLen);
} catch (IllegalArgumentException e) {
    pw = PasswordGen.generatePassword(12, 16); // sane defaults
}

When it happens

Trigger: Calling generatePassword(minLength, maxLength) where minLength > maxLength, or minLength <= 0, or maxLength <= 0.

Common situations: Config with min greater than max (e.g. min=12, max=8); a 'min length' default of 0; UI controls allowing 0; bounds computed from user input without ordering/sanity checks.

Related errors

• Damping factor must be between 0 and 1
• Bit length must be at least {} for security.
• Given range of values is invalid!
• Input '{input}' contains not only digits
• Position must be between 0 and {array.length}

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/9253a6d7298dc3f6. Report an issue: GitHub.