Print the Duplicate Letters in a String in Java

package com.sk.demos;

import java.util.*;

public class FindDuplicates {

    public static void main(String[] args) {

        String input = "SURESH";

        

        // Call the function to print duplicate characters

        printDuplicates(input);

    }

    // Function to print duplicate characters using List

    public static void printDuplicates(String input) {

    // List to keep track of characters we've seen

        List<Character> seen = new ArrayList<>();  

     // Set to store duplicates

        Set<Character> duplicates = new HashSet<>();  

        

        // Iterate through the string and identify duplicates

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

            char ch = input.charAt(i);

            

            // Check if we've seen the character already

            if (seen.contains(ch)) {

            // Add to duplicates if it's already in seen

                duplicates.add(ch);  

            } else {

            // Otherwise, add it to the seen list

                seen.add(ch); 

            }

        }

        

        // Print duplicates

        if (duplicates.isEmpty()) {

            System.out.println("No duplicate characters found.");

        } else {

            System.out.println("Duplicate characters:");

            for (char ch : duplicates) {

                System.out.println(ch);

            }

        }

    }

}

output:

============

S