public class IsStringHavingUniqueChar { public static void main(String[] args) { System.out.println("isStringHavingUniqueCharacters: "+isStringHavingUniqueCharacters("Raaaahul")); } private static boolean isStringHavingUniqueCharacters(String str){ boolean[] asciiArray = new boolean[256]; for (int i = 0; i < str.length(); i++) { int charAscii = str.charAt(i); if(asciiArray[charAscii]) return false; asciiArray[charAscii] = true; } return true; } }