Check the keys in the map matching with the List content in Java

Question

I have a List of Strings and a Map. Every key in the map needs to present in the list else I need to throw an exception. As of now I am looping the list and checking the key and throw exception if the map doesn't contains the key. Below is the sample code is what I am doing. IS there any other way in Java8 we can do it in one line or something using streams and filters ?

And also the contents in the list and keys in the map should match. That I am already handling in the separate if condition.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TestClass {

    public static void main(String[] args) {

        List<String> ll = new ArrayList<>();
        Map<String, Integer> m = new HashMap<>();
        ll.add("a");
        ll.add("b");
        ll.add("d");

        m.put("a", 1);
        m.put("b", 1);
        m.put("c", 1);

        if(ll.size() != m.size){
       System.out.println("Throw Exception");
         }

        for(String s : ll) {

            if(!m.containsKey(s)) {
                System.out.println("Throw Exception");
            }
        }
    }
}

Answer 1

Every key in the map needs to present in the list else I need to throw an exception

You could do it using Stream.anyMatch and iterating on the keyset of the map instead as (variable names updated for readability purpose) :

if(map.keySet().stream().anyMatch(key -> !list.contains(key))) {
    throw new CustomException("");
}

Better and as simple as it gets, use List.containsAll :

if(!list.containsAll(map.keySet())) {
    throw new CustomException("");
} 

Important: If you can trade for O(n) space to reduce the runtime complexity, you can create a HashSet out of your List and then perform the lookups. It would reduce the runtime complexity from O(n^2) to O(n) and the implementation would look like:

Set<String> allUniqueElementsInList = new HashSet<>(list);
if(!allUniqueElementsInList.containsAll(map.keySet())) {
    throw new CustomException("");
}

Answer 2

We can try adding the list to a set, then comparing that set with the keyset from your hashmap:

List<String> ll = new ArrayList<>();
ll.add("a");
ll.add("b");
ll.add("d");

Map<String, Integer> m = new HashMap<>();
m.put("a", 1);
m.put("b", 1);
m.put("c", 1);

Set<String> set = new HashSet<String>(ll);

if (Objects.equals(set, m.keySet())) {
    System.out.println("sets match");
}
else {
    System.out.println("sets do not match");
}