Question

In C++, I can look up a key in a map and insert it if it’s not there for the cost of a single look up. Can I do the same in Java?

Update:

(For those of you who must see code.)

long id = 0xabba;
int version = 0xb00b;  
for (List<Object> key : keys) {
    if (!index.containsKey(key)) {
      index.put(key, Maps.<Long,Integer>newHashMap());
    }
    index.get(key).put(id, version);
}

There are two look ups when the key is first inserted into the map. In C++, I could do it with a single look up.

Answer 1

Concurrent maps have an atomic putIfAbsent method, if this is what you mean.