Java program to print all duplicate characters in a string

// Java program for the above approach
import java.util.*;
class GFG {

    // Function to print all duplicate
    // characters in string using HashMap
    public static void
    countDuplicateCharacters(String str)
    {

        // Creating a HashMap containing char
        // as a key and occurrences as a value
        Map<Character, Integer> map
            = new HashMap<Character, Integer>();

        // Converting given string into
        // a char array
        char[] charArray = str.toCharArray();

        // Checking each character
        // of charArray
        for (char c : charArray) {

            if (map.containsKey(c)) {

                // If character is present
                // in map incrementing it's
                // count by 1
                map.put(c, map.get(c) + 1);
            }
            else {

                // If character is not present
                // in map putting this
                // character into map with
                // 1 as it's value.
                map.put(c, 1);
            }
        }

        // Traverse the HashMap, check
        // if the count of the character
        // is greater than 1 then print
        // the character and its frequency
        for (Map.Entry<Character, Integer> entry :
             map.entrySet()) {

            if (entry.getValue() > 1) {
                System.out.println(entry.getKey()
                                   + " : "
                                   + entry.getValue());
            }
        }
    }

    // Driver Code
    public static void
    main(String args[])
    {
        // Given String str
        String str = "geeksforgeeks";

        // Function Call
        countDuplicateCharacters(str);
    }
}