Java String Manipulation : Comparing adjacent Characters in Java

Question

i have the following problem
Given a string, return a \"cleaned\" string where adjacent chars that are the same have been reduced to a single char. So \"yyzzza\"

Answer 1

public static String stringClean(String str) {
    if (str == null || "".equals(str)) {
        return str;
    }
    char lastChar = str.charAt(0);
    StringBuilder resultBuilder = new StringBuilder();
    resultBuilder.append(lastChar);
    for (int index = 1; index < str.length(); index++) {
        char next = str.charAt(index);
        if (lastChar != next) {
            resultBuilder.append(next);
            lastChar = next;
        }
    }

    return resultBuilder.toString();
}