Add value to List inside Map<String, List> in Java 8 [duplicate]

Question

Is there a better way in Java 8 to add a value to a List inside of a Map?

In java 7 i would write:

Map<String, List<Integer>> myMap = new HashMap<>(); ... if (!myMap.containsKey(MY_KEY)) {     myMap.put(MY_KEY, new ArrayList<>()); } myMap.get(MY_KEY).add(value);          

Answer 1

You should use the method Map::computeIfAbsent to create or get the List:

myMap.computeIfAbsent(MY_KEY, k -> new ArrayList<>()).add(value);