FindDuplicateCharacters.java

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;

/**
 * Java Program to find duplicate characters in String.
 */
public class FindDuplicateCharacters {
    public static void main(String args[]) {
        printDuplicateCharacters("Programming");
        printDuplicateCharacters("Language");
        printDuplicateCharacters("HelloWorld");
        printDuplicateCharacters("Java");
    } /* * Find all duplicate characters in a String and print each of them. */

    public static void printDuplicateCharacters(String word) {
        char[] characters = word.toCharArray();
        Map<Character, Integer> charMap = new HashMap<Character, Integer>();
        for (Character ch : characters) {
            if (charMap.containsKey(ch)) {
                charMap.put(ch, charMap.get(ch) + 1);
            } else {
                charMap.put(ch, 1);
            }
        }
        Set<Map.Entry<Character, Integer>> entrySet = charMap.entrySet();
        System.out.printf("List of duplicate characters in String '%s' %n", word);
        for (Map.Entry<Character, Integer> entry : entrySet) {
            if (entry.getValue() > 1) {
                System.out.printf("%s : %d %n", entry.getKey(), entry.getValue());
            }
        }
    }
}