StringUtils.java

/**
 * StringUtils - Utility class for common String manipulations.
 * Focuses on null-safe operations and text formatting.
 */
public final class StringUtils {

    // Private constructor to prevent instantiation
    private StringUtils() {
        throw new UnsupportedOperationException("Utility class");
    }

    /**
     * Checks if a string is null or consists only of whitespace.
     * @param str the string to check
     * @return true if the string is null, empty, or whitespace
     */
    public static boolean isBlank(String str) {
        return str == null || str.trim().isEmpty();
    }

    /**
     * Capitalizes the first letter of a string.
     * @param str the string to capitalize
     * @return the capitalized string, or the original if empty/null
     */
    public static String capitalize(String str) {
        if (isBlank(str)) return str;
        return str.substring(0, 1).toUpperCase() + str.substring(1);
    }

    /**
     * Truncates a string to a specific length and adds an ellipsis (...) if truncated.
     * @param str the string to truncate
     * @param maxLength the maximum allowed length (including dots)
     * @return the truncated string
     */
    public static String abbreviate(String str, int maxLength) {
        if (str == null || str.length() <= maxLength) return str;
        if (maxLength < 3) return str.substring(0, maxLength);
        return str.substring(0, maxLength - 3) + "...";
    }

    /**
     * Reverses the characters in a string.
     * @param str the string to reverse
     * @return the reversed string, or null if input was null
     */
    public static String reverse(String str) {
        if (str == null) return null;
        return new StringBuilder(str).reverse().toString();
    }

    /**
     * Counts how many times a substring appears in a larger string.
     * @param str the main string
     * @param sub the substring to look for
     * @return the number of occurrences
     */
    public static int countOccurrences(String str, String sub) {
        if (isBlank(str) || isBlank(sub)) return 0;
        int count = 0;
        int lastIndex = 0;
        while ((lastIndex = str.indexOf(sub, lastIndex)) != -1) {
            count++;
            lastIndex += sub.length();
        }
        return count;
    }
}