Best practice to find Duplicate Character from a String in java

This program could be the best way to find the number of duplicate characters from the given String. Here we are using Map and Set from java.util.Collections package. In the below program we are using Set to collect different characters from the given String. One boolean variable and one method named as findDuplicateChar(String myString) to find the duplicates. Also some known methods like toCharArray() to convert String to character array and for-each loop to iterate Set and Array. Better you can go through the given program to find duplicate characters from the given String.

Program:

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
/**
 * @author javabynataraj.blogspot.com
 * 
 */
public class FindDuplicateCharFromString {

 Map<Character, Integer>  allDuplicate;

 // Returns a Set view of the keys contained in this map
 Set<Character>  Keys;
 static boolean amIDuplicate;
 public static boolean isAmIDuplicate() {
  return amIDuplicate;
 }
 public void setAmIDuplicate(boolean amIDuplicate) {
  FindDuplicateCharFromString.amIDuplicate = amIDuplicate;
 }
 public static void main(String a[]) {
  System.out.println(" **** http://javabynataraj.blogspot.com **** ");
  FindDuplicateCharFromString object = new FindDuplicateCharFromString();

  // Test1
  object. findDuplicateChar("javabynataraj blog");
  System.out.println("Any Duplicate Char? " + isAmIDuplicate());

  // Test2
  object. findDuplicateChar("no duplicate");
  System.out.println("Any Duplicate Char? " + isAmIDuplicate());
 }
 public void  findDuplicateChar(String mySting) {
   allDuplicate = new HashMap<Character, Integer>();
   Keys =  allDuplicate.keySet();
  setAmIDuplicate(false);
  char[] charArr = mySting.toCharArray();

  // Iterate through String
  for (Character myChar : charArr) {
   if ( allDuplicate.containsKey(myChar)) {

    // Just increment counter if Character presents
    allDuplicate.put(myChar,
      allDuplicate.get(myChar) + 1);
   } else {
    allDuplicate.put(myChar, 1);
   }
  }
  System.out.println("n========== Let's print all results. Here is a String: "+ mySting + " ==========");
  for (Character myChar :  Keys) {
   if ( allDuplicate.get(myChar) > 1 &&  allDuplicate != null) {
    setAmIDuplicate(true);
    System.out.println("Character " + myChar + " appeared " +  allDuplicate.get(myChar) + " times");
   }
  }
 }
}

Output: