Mfrhtyj

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");

            }

        }

    }

}

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("");

}

Try this:

if ((ll == null && m == null) ||                            // if both are null

   ((ll.size() == m.size() && m.keySet().containsAll(ll)))  // or contain the same elements

) {

    System.out.println("Collections contain the same elements");

} else {

    throw new CustomException("Collections don't match!");

}

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");

}

Simply use the following :-

m.keySet().stream().filter(e -> !ll.contains(e)).findAny()

                     .ifPresent(e -> throwException("Key Not found : " + e));

And define the throwException method below :

public static void throwException(String msg) {

    throw new RuntimeException(msg);

}

You can simply change your existing code to -

if(!m.keySet().containsAll(ll)) {

    System.out.println("Throws Exception");

}

This will solve your problem. :)