Key existence checking utility in Map

Question

I'm using the following code for checking if a key exists in a Map instance:

if (!map_instance.containsKey(key))     throw new RuntimeException("Specified key doesn't exist in map"); else    return map_instance.get(key); 

My question is:

Is there a utility or Map implementation to simplify the above code, such as:

custom_map.get(key,"Specified key doesn't exist in map"); 

My goal is: if key does not exist in map, the map implementation throws an exception with the passed string.

I don't know whether or not my desire is reasonable?

(Sorry if I am using the wrong terminology or grammar, I am still learning the English language.)

Answer 1

I use Optional Java util class, e.g.

Optional.ofNullable(elementMap.get("not valid key"))             .orElseThrow(() -> new ElementNotFoundException("Element not found")); 

Answer 2

In Java 8 you can use computeIfAbsent from Map, like this:

map.computeIfAbsent("invalid", key -> { throw new RuntimeException(key + " not found"); });