Get first non-repeating Letter

import java.util.HashMap;

import java.util.LinkedHashMap;
import java.util.Map;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

public class Check {
    public static String firstNonRepeatingLetter(String str) {
        String val=null;
        char[] var=str.toCharArray();
        LinkedHashMap<Character, Integer> map = new LinkedHashMap<>();
        for(int i=0;i<var.length;i++){
            if(map.containsKey(var[i])){
                map.put(var[i],map.get(var[i])+1);}
            else {
                map.put(var[i], 1);
            }
        }
        for (Map.Entry<Character, Integer> entry : map.entrySet()){
            if(entry.getValue()==1) {
                val = Character.toString(entry.getKey());
                break;
            }
        }


        return val;
    }

    public static void main(String[] args) {
        System.out.println(firstNonRepeatingLetter("moonmen"));
    }

}