/**
 * Checks whether a string consists only of alphanumeric characters.
 *
 * This function verifies if the string is composed within the specified
 * range of length and consists only of alphanumeric characters.
 *
 * @param str The input string.
 * @param minLength The minimum number of characters (treated as 1 if null).
 * @param maxLength The maximum number of characters (treated as the string's length if null).
 * @return true if the input string meets the conditions, otherwise false.
 * @throws IllegalArgumentException Throws an exception if the minimum length is less than 1,
 *                                  or the maximum length is less than the minimum length.
 */
public static boolean isAlphanumeric(String str, Integer minLength, Integer maxLength) {
    if (str == null) {
        throw new IllegalArgumentException("Input string must not be null.");
    }

    int min = (minLength == null) ? 1 : minLength;
    int max = (maxLength == null) ? str.length() : maxLength;

    // Validate the arguments
    if (min < 1) {
        // Throw an exception if the minimum length is less than 1
        throw new IllegalArgumentException("The minimum length must be an integer greater than or equal to 1.");
    }

    if (maxLength != null && max < min) {
        // Throw an exception if the maximum length is less than the minimum length
        throw new IllegalArgumentException("The maximum length must be greater than or equal to the minimum length.");
    }

    // Build the regex pattern
    String regex = (maxLength == null)
        ? String.format("^[a-zA-Z0-9]{%d,}$", min)            // When the maximum length is not specified
        : String.format("^[a-zA-Z0-9]{%d,%d}$", min, max);    // When the range is specified

    // Validate the string using the regex pattern
    return Pattern.matches(regex, str);
}

import java.util.regex.Pattern;

public class Main {

    /**
     * Checks whether a string consists only of alphanumeric characters.
     *
     * This function verifies if the string is composed within the specified
     * range of length and consists only of alphanumeric characters.
     *
     * @param str The input string.
     * @param minLength The minimum number of characters (treated as 1 if null).
     * @param maxLength The maximum number of characters (treated as the string's length if null).
     * @return true if the input string meets the conditions, otherwise false.
     * @throws IllegalArgumentException Throws an exception if the minimum length is less than 1,
     *                                  or the maximum length is less than the minimum length.
     */
    public static boolean isAlphanumeric(String str, Integer minLength, Integer maxLength) {
        if (str == null) {
            throw new IllegalArgumentException("Input string must not be null.");
        }

        int min = (minLength == null) ? 1 : minLength;
        int max = (maxLength == null) ? str.length() : maxLength;

        // Validate the arguments
        if (min < 1) {
            // Throw an exception if the minimum length is less than 1
            throw new IllegalArgumentException("The minimum length must be an integer greater than or equal to 1.");
        }

        if (maxLength != null && max < min) {
            // Throw an exception if the maximum length is less than the minimum length
            throw new IllegalArgumentException("The maximum length must be greater than or equal to the minimum length.");
        }

        // Build the regex pattern
        String regex = (maxLength == null)
            ? String.format("^[a-zA-Z0-9]{%d,}$", min)            // When the maximum length is not specified
            : String.format("^[a-zA-Z0-9]{%d,%d}$", min, max);    // When the range is specified

        // Validate the string using the regex pattern
        return Pattern.matches(regex, str);
    }

    /**
     * Main method for testing the functionality of the isAlphanumeric method.
     *
     * @param args Command-line arguments (not used)
     */
    public static void main(String[] args) {
        // Test Case 1: Valid input (meets the condition)
        System.out.println("Test Case 1: " + isAlphanumeric("hello123", 3, 10)); // true

        // Test Case 2: Does not meet the minimum length
        System.out.println("Test Case 2: " + isAlphanumeric("hello123", 10, null)); // false

        // Test Case 3: Contains non-alphanumeric characters
        System.out.println("Test Case 3: " + isAlphanumeric("hello!123", 1, null)); // false

        // Test Case 4: Exceeds the maximum length
        System.out.println("Test Case 4: " + isAlphanumeric("abc", null, 2)); // false

        // Test Case 5: Valid input (contains only alphanumeric characters)
        System.out.println("Test Case 5: " + isAlphanumeric("ABC123", 1, 6)); // true

        // Test Case 6: Empty string
        System.out.println("Test Case 6: " + isAlphanumeric("", 1, null)); // false

        // Test Case 7: Contains only alphanumeric characters within the specified range
        System.out.println("Test Case 7: " + isAlphanumeric("test123", 4, 8)); // true

        // Test Case 8: No maximum length specified, meets the condition
        System.out.println("Test Case 8: " + isAlphanumeric("abcdef123", 5, null)); // true

        // Test Case 9: Length matches the minimum length
        System.out.println("Test Case 9: " + isAlphanumeric("abc", 3, 5)); // true

        // Test Case 10: Length matches the maximum length
        System.out.println("Test Case 10: " + isAlphanumeric("abcde", 1, 5)); // true
    }
}