Find out duplicate characters in a string

package com.coding.core;

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

public class FindDuplicateCharactersInString {

public static void main(String[] args) {
String str = "programming";
FindDuplicateCharactersInString.findDuplicateChars(str);

}

@SuppressWarnings("rawtypes")
public static void findDuplicateChars(String str) {
char ch[] = str.toCharArray();
Map<Character, Integer> charMap = new HashMap<Character, Integer>();
for (char c : ch) {

charMap.put(c, charMap.get(c) != null ? charMap.get(c) + 1 : 1);
}

Set<Map.Entry<Character, Integer>> entrys = charMap.entrySet();
for (Entry e : entrys) {
System.out.println(e.getKey() + "--->" + e.getValue());
}

}

}