Program to Find Duplicate Characters in a string in Java

Hello, In this post we will see Program to find duplicate characters in a string in Java, find duplicate characters in a string java without using hashmap, program to remove duplicate characters in a string in java etc.

Program to find duplicate characters in String in a Java

package Practice;
import java.util.HashMap;
import java.util.Set;
public class FindDuplicateCharinWord {

    public static void main(String[] args) {

        String str = "Pune is a green city";
        String s1 = str.replaceAll("\\s", "");

        // Converting given string to char array
        char[] c = s1.toCharArray();

        // Creating HashMap containing char as key and it's occurrences as value
        HashMap<Character, Integer> m = new HashMap<Character, Integer>();

        // Checking each character of c
        for (Character ch : c) {

            if (m.containsKey(ch)) {

                m.put(ch, m.get(ch) + 1);

            } else {

                m.put(ch, 1);



        // getting a set which containing all keys of m hashmap
        Set<Character> s = m.keySet();

        for (Character c1 : s) {

            if (m.get(c1) > 1) {

                System.out.println(c1 + "-->" + m.get(c1));







Explanation: In the above program, we have used HashMap and Set for finding the duplicate character in a string. First we have converted the string into array of character. Then create a hashmap to store the Characters and their occurrences. Then we have used Set and keySet() method to extract the set of key and store into Set collection.

Program to remove duplicate characters in a string in java

If you are not using HashMap then you can iterate the passed String in an outer and inner loop and check if the characters are equal or not. If equal, then increment the count. In case characters are equal you also need to remove that character from the String so that it is not counted again in further iterations.

public class DuplicateChars {

  public static void main(String[] args) {   
    findDuplicateCharsWithCount("kakatua parrot is a bird");
    findDuplicateCharsWithCount("John was jealous");
  private static void findDuplicateCharsWithCount(String str) {
    System.out.println("Duplicates in- "+ str);
    int count;
    for(int i = 0; i < str.length(); i++) {
      count = 1;
      //Take one char at a time
      char c = str.charAt(i);
      // don't count the spaces
      if(c == ' ') 
      for(int j = i + 1; j < str.length(); j++) {
        if(c == str.charAt(j)) {
          // remove the char so that it is not picked again
          // in another iteration
          str = str.substring(0, j) + str.substring(j+ 1);
      if(count > 1) {
        System.out.println(c + " found " + count + " times");

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