为什么我不能在Java中使用'long'类型创建HashMap？

Question

有什么理由不允许以下情况？

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

Answer 1

你正在使用原语重写为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