Method toUpperCase

src/main/java/com/thealgorithms/strings/Upper.java:23–42

Converts all the characters in this String to upper case. @param s the string to convert @return the String, converted to uppercase.

(String s)

     * @return the {@code String}, converted to uppercase.
     */
    public static String toUpperCase(String s) {
        if (s == null) {
            throw new IllegalArgumentException("Input string cannot be null");
        }
        if (s.isEmpty()) {
            return s;
        }

        StringBuilder result = new StringBuilder(s.length());

        for (int i = 0; i < s.length(); ++i) {
            char currentChar = s.charAt(i);
            if (Character.isLowerCase(currentChar)) {
                result.append(Character.toUpperCase(currentChar));
            } else {
                result.append(currentChar);
            }
        }
        return result.toString();
    }
}