Putting a new value into a Map if not present, or adding it if it is

Question

I have a java.util.Map for a key-type class Foo. Let\'s call the instance of the map map.

I want to add {

Answer 1

You can do:

map.put(foo, f + map.getOrDefault(foo, 0d));

The value here will be the one that corresponds to foo if present in the Map or 0d, otherwise.