duplicate_words in string

import java.util.*;

public class HelloWorld{

    public static void main(String []a)
    {
        printchar("javahaha");
       
    }
    public static void printchar(String str){
        if(str==null)
        {
            System.out.println("Null string");
            return;
        }
        if(str.length()==1)
        {
            System.out.println("single length string");
            return;
        }
        if(str.isEmpty())
        {
            System.out.println("Empty string");
            return;
        }
        
        // step 1 is to convert the string into character array
        char words[] = str.toCharArray();
        
        //maintain hashmap<key, value>
        Map<Character, Integer> charMap = new HashMap<Character, Integer>();
        
        for(Character ch : words )
        {
            if(charMap.containsKey(ch)){
                charMap.put(ch, charMap.get(ch)+1);
            }else{
                charMap.put(ch,1);
            }
        }
        
        //print the map
        Set<Map.Entry<Character, Integer>> entrySet = charMap.entrySet();
        for(Map.Entry<Character,Integer> entry : entrySet)
        {
            if(entry.getValue()>1)
            {
                System.out.println(entry.getKey() + " : " + entry.getValue());
            }
        }
    }
}