mjhjmtu

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. :)