Why can I not create a HashMap with 'long' types in Java?

Question

Any reason that the following is not allowed?

HashMap<long, long> x = new HashMap<>();

Answer 1

you're using primitives rewrite to HashMap<Long,Long> x = new HashMap<>()

Answer 2

In Java, types with generic type parameters, such as HashMap, only accept types that inherit from Object. long does not inherit from Object, so you can't use it with HashMap. You can however use Long, which is a boxed version of long.

Answer 3

Using standard collections for primitive types like long is not really effective

If you need to minimize memory footprint and get better performance you should consider 3rd-party collection libraries like Trove