Unique Character

public class que1_array_unique {
    public static boolean isUnique(String str) {
        boolean[] char_set = new boolean[256];
        for (int i = 0; i < str.length(); i++) {
            int val = str.charAt(i);
            if (char_set[val]) return false;
            char_set[val] = true;
        }
        return true;
    }

    public static void main(String[] args) {

        String[] words = {"abcde", "hello", "apple", "kite", "padle"};

        System.out.println("It will print true for Unique Characters\n");
        for (String word : words) {
            System.out.println(word + ": " + isUnique(word)+"\n");
        }
    }
}