Find Duplicates in String using hashing

// It is O(n) time

class DuplicatesInString {

    // Asumption : All characters are in ASCII code

    static void printDuplicates(String str) {

        int[] frequency = new int[128];

        for(int i = 0; i < str.length(); i++) {

            frequency[str.charAt(i)]++;

        }

        System.out.println("Printing duplicates : ");

        for(int i = 0; i < str.length(); i++) {

            char ch = str.charAt(i);

            if(frequency[ch] > 1) {

                System.out.println(ch + " appears " + frequency[ch] + " times.");

                frequency[ch] = 0; // To avoid print duplicate result

            }  

        }

    }

public static void main (String[] args) {

String str = "Compile run your code with the CodeChef online IDE. Our online compiler"

            + "supports multiple programming languages like Python, C++, C, Kotlin,"

            + "NodeJS, and many more.";

        printDuplicates(str);

}

}