GetOrDefult return Array which I can not change

I have below code

Map<String, List<String> myMap = new HashMap();
...
myMap
  .getOrDefault("key", new ArrayList<>())
  .add("value");

My expectation is that in case there is no value (Array) in map, it will return reference to newly created array, which I can add my "value" to.

However I see that myContext map is empty. Seems super basic, I don’t get it.

>Solution :

getOrDefault() – is meant for accessing the value, not for modifying the map.

If you need to modify the map, you can use instead putIfAbsent(), be aware that it return a value that was previously associated with the key (and in case the key was not present it returns null). For the snippet you’ve introduced, a more suitable option would be computeIfAbsent() which returns the current value.

Map<String, List<String>> myMap = new HashMap<>();
        
myMap.computeIfAbsent("key", k -> new ArrayList<>())
    .add("value");