Custom function to check whether 2 HashMaps are equal is not working in Java

Question

I'm trying to check whether 2 HashMaps are equal using a custom function match. I expect the output to be true, but the program outputs false. Here is the code snippet.

import java.util.HashMap;

public class HashMapEquals{

    private static boolean matches1(HashMap<Character, Integer> one, HashMap<Character, Integer> two){
        for(char c: one.keySet()){
            if(one.get(c) != two.get(c))
                return false;
        }
        return true;
    }

    private static boolean matches2(HashMap<Character, Integer> one, HashMap<Character, Integer> two){
        for(char c: two.keySet()){
            if(two.get(c) != one.get(c))
                return false;
        }
        return true;
    }

    private static boolean matches(HashMap<Character, Integer> one, HashMap<Character, Integer> two){
        boolean first = matches1(one, two);
        boolean second = matches2(one, two);
        System.out.println(first);
        System.out.println(second);
        return (first && second);
    }

    public static void main(String args[]){
        HashMap<Character, Integer> one = new HashMap<>();
        HashMap<Character, Integer> two = new HashMap<>();

        one.put('a', 10000);
        two.put('a', 10000);

        matches(one, two);
        System.out.println(one.equals(two));
    }
}

The output is

$ java HashMapEquals
  false
  false
  true

I know we can check the same functionality using the inbuilt function of hashmap one.equals(two) which is working as expected. But, I am just curious to know what is wrong with the custom function matches in the above code snippet.

score 2 · Accepted Answer · answered Feb 05 '23 at 04:04

Use Objects.equals instead of == or != to compare non-primitives that might be null. Note that you should check that the two Maps have the exact same size instead of doing the value check both ways.

if (!Objects.equals(one.get(c), two.get(c))) return false;

Custom function to check whether 2 HashMaps are equal is not working in Java

1 Answers1