Static method to count occurrences of a letter in a lower case word using maps

I have to create a class called MakeMap with a single static method called countLetters(). The method should take as a parameter a word formed of lowercase letters and return a map of the counts of the letters in the word.
This is the test code for the Main class (which I cannot edit):

import java.util.Map;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
public class Main
{
public static void main(String [] args)
{
Map<Character, Integer> count = MakeMap.countLetters("hello");
List<Character> letters = new ArrayList<Character>(count.keySet());
Collections.sort(letters);
for(Character letter : letters)
System.out.println("There are " + count.get(letter) + " of the letter '" + letter + "'");
}
}

The output must be formatted like this also:
$ java Main
There are 1 of the letter 'e'
There are 1 of the letter 'h'
There are 2 of the letter 'l'
There are 1 of the letter 'o'

This is what I have attempted so far in my MakeMap class. I feel like I only need a couple of minor adjustments to get this working.

import java.util.Map;
import java.util.TreeMap;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
public class MakeMap
{
public static Map countLetters(String word)
{
HashMap<Character, Integer> charCountMap = new HashMap<Character, Integer>();
String w = word.toLowerCase();
// checking each char of strArray 
for(int i = 0; i < word.length(); i++)
{
if(charCountMap.containsKey(word.charAt(i)))
{ 
// If char is present in charCountMap, 
// incrementing it's count by 1 
charCountMap.put(word.charAt(i), charCountMap.get((word.charAt(i)) + 1 ));
} 
else
{ 
// If char is not present in charCountMap, 
// putting this char to charCountMap with 1 as it's value 
charCountMap.put(word.charAt(i), 1); 
}
}
return charCountMap;
}
}

This is the error message I am getting:
Note: Main.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

Incorrect brackets, should be:

charCountMap.put(word.charAt(i), (charCountMap.get(word.charAt(i)) + 1));

additionaly you must return charCountMap from this method isntead of print it out there, so the method must be defined as public static Map<Character, Integer> countLetters(String word)

Hello You have problem here :

 charCountMap.put(word.charAt(i), charCountMap.get((word.charAt(i)) + 1 ));

Must be

charCountMap.put(word.charAt(i), charCountMap.get((word.charAt(i))) + 1 );

And you should return charCountMap;

As already said, countLetters() returns void in your implementation; the given code expects it to return a HashMap<Character, Integer>. You can return your charCountMap at the end of the method and it'll work.

Some additional notes:

You have a line
String w = word.toLowerCase();.
that doesn't do anything, since you never use w again; you'll want to change it to word.

Lastly, the bracketing error could have easily been avoided if you did something like
char curr = word.charAt(i);
in the loop and then used curr instead of word.charAt(i). Makes it easier to read and looks cleaner.