Write a Java program to find number of occurrence of duplicate characters in a String using HashMap.

Check below code:

import java.io.IOException;
import java.util.HashMap;
import java.util.Map.Entry;

public class DuplicateCharacterOrNot
{
    public static void main(String args[]) throws NumberFormatException, IOException
    {
        duplicateCharCount("ProgramsBuzz");
        duplicateCharCount("Learn Java");
        duplicateCharCount("Better"); 
    }
	
    static void duplicateCharCount(String inputString)
    {
        HashMap<Character, Integer> charCountMap = new HashMap<Character, Integer>();
		 
        //Convert String to char array
        char[] strArray = inputString.toCharArray();
		 
        for (char c : strArray)
        {
            if(charCountMap.containsKey(c))
            {
                //Increment count by one if character present in hashmap
                charCountMap.put(c, charCountMap.get(c)+1);
            }
            else
            {
                //If char is not present then put first value as 1
                charCountMap.put(c, 1);
            }			 
        }
		 
        System.out.println("Duplicate Characters Count in String: "+inputString);
        for (Entry<Character, Integer> entry : charCountMap.entrySet()) 
        {
            if(entry.getValue() > 1)
                System.out.println(entry.getKey() + " = " + entry.getValue());
        }
    }
}

Output

Duplicate Characters Count in String: ProgramsBuzz

r = 2

z = 2

Duplicate Characters Count in String: Learn Java

a = 3

Duplicate Characters Count in String: Better

t = 2

e = 2