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

Question

I saw this code today:

    ImmutableMap<Class<? extends ClientCommand>, CommandProcessorInterface> immutableMap =
            ImmutableMap.<Class<? extends  ClientCommand>, CommandProcessorInterface>of(...

What does this syntax mean?

ImmutableMap.<Class ..

I knew generics was right after the class name. No?

What is the difference between:

ImmutableMap<Class.. and ImmutableMap.<Class..

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.<Type>genericStaticMethod();

And to answer you final question:

What is the difference between ImmutableMap<Class...> and ImmutableMap.<Class... ?

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.