ValidationUtils.java

/**
 * ValidationUtils - Utility class for common validation checks
 * ToDo: Add more methods for collections, maps, regex, etc.
 */
public final class ValidationUtils {

    private ValidationUtils() {
        throw new UnsupportedOperationException("Utility class");
    }

    /**
     * Check that an object reference isn't null; throw error if it is
     * @param obj the object to check
     * @param message the exception message if null
     * @throws NullPointerException if the object is null
     */
    public static <T> T requireNonNull(T obj, String message) {
        if (obj == null) {
            throw new NullPointerException(message);
        }
        return obj;
    }

    /**
     * Make sure a number is within a specified range (double and int overloads)
     * @param value the value to check
     * @param min the minimum allowed value
     * @param max the maximum allowed value
     * @param fieldName the name of the variable (for error message)
     * @throws IllegalArgumentException if the value is out of range
     */
    public static void checkRange(double value, double min, double max, String fieldName) {
        if (value < min || value > max) {
            throw new IllegalArgumentException(
                String.format("%s must be between %.2f and %.2f. Found: %.2f", fieldName, min, max, value)
            );
        }
    }
    public static void checkRange(int value, int min, int max, String fieldName) {
        if (value < min || value > max) {
            throw new IllegalArgumentException(
                String.format("%s must be between %d and %d. Found: %d", fieldName, min, max, value)
            );
        }
    }

    /**
     * Check if a condition is true; error iffalse.
     * @param condition the boolean condition to check
     * @param message the exception message if false
     * @throws IllegalArgumentException if the condition is false
     */
    public static void checkArgument(boolean condition, String message) {
        if (!condition) {
            throw new IllegalArgumentException(message);
        }
    }

    /**
     * Ensures a string is not null or empty.
     * @param str the string to check
     * @throws IllegalArgumentException if string is null or empty
     */
    public static void rejectEmpty(String str, String fieldName) {
        if (str == null || str.isEmpty()) {
            throw new IllegalArgumentException(fieldName + " cannot be null or empty");
        }
    }
}