CamelCaseImplement.java

/** 
 * CamelConverter makes
 *   first word all lower
 *   subsequent words firt letter upper, rest lower
 *   "TWO", "WORDS" -> "twoWords"
 */
class CamelConverter implements CaseConverter {

    @Override
    public String convert(String... words) {

        // Accumulate result in StringBuilder
        StringBuilder result = new StringBuilder();
        
        // First word is all lower
        result.append(
            words[0]
                .trim()
                .toLowerCase()
        );

        // Subsequent words are
        // first -> upper
        // rest -> lower
        for (int offset = 1; 
             offset < words.length; 
             offset++) {

            // First letter is upper
            result.append(
                words[offset]
                   .substring(0, 1)
                   .toUpperCase()
            );

            // Remaining letters are lower
            result.append(
                words[offset]
                    .substring(1)
                    .toLowerCase());
        }
        return result.toString();
    }
}