Remove duplicate characters contained in the second string from the first String

RemoveDuplicateString.java

package kata.string;

public class RemoveDuplicateString {

    public static String removeDuplicateCharacters(String first, String second) {
        if (first == null || second == null) { return first; }

        char[] map = new char[256];
        for (int i = 0; i < second.length(); i++) {
            char ch = second.charAt(i);
            map[ch] = 1;
        }

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < first.length(); i++) {
            char ch = first.charAt(i);
            if (!(map[ch] == 1)) {
                sb.append(ch);
            }
        }

        return sb.toString();
    }

}