Weird Java generic

Question

What does this mean?

HashBiMap<Character, Integer> charOcc = HashBiMap.<Character, Integer> create();

Answer 1

create() is a generic method. Since it's static and has no parameters (hence no type inference), the only way you can tell it what the generic parameters are is by that strange-looking .<Character, Integer> syntax.

Edit: This is actually not necessary in this specific case; the compiler can infer the generic types from the left-hand side. But it is sometimes necessary in other cases, such as this question: Generic method in Java without generic argument

Answer 2

It's calling a generic static method (create()) using Character and Integer as the type arguments. For instance, if you're looking at the Google Java Collections, the declaration has this signature:

public static <K,V> HashBiMap<K,V> create()

The <K,V> part on its own specifies that those are type parameters for the method.

The equivalent call in C# would be one of:

HashBiMap.Create<Character, Integer>();
HashBiMap<Character, Integer>.Create();

depending on whether you wanted it to be a generic method in a nongeneric type, or a nongeneric method in a generic type.

The positioning of type parameters and type arguments in Java is unintuitive IMO.