What does the dot operator `.` (before the generic parameter) mean?

Question

I saw this code today:

    ImmutableMap, CommandProcessorInterface> immutableMap =
            ImmutableMap.

        

Answer 1

It means you're invoking a generic static method, called of in the ImmutableMap class.

It's pretty much the same as you're invoking a static method, nested in some class:

SomeClass.staticMethod();

For the cases when your method has a type-parameter defined, you can explicitly provide the generic type and this is done like this:

SomeClass.genericStaticMethod();

And to answer you final question:

What is the difference between ImmutableMap and ImmutableMap. ?

The first is usually used when creating an instance of a generic class. It's used to define the generic-type on class level, while the second is used to invoke a generic static method that's nested in some class.