How to use a method reference on a static import?

Question

When using map functions in java I can do the following:

import com.example.MyClass;  someStream.map(MyClass::myStaticMethod) 

but in my project we sometimes use static imports, how can I reference the myStaticMethod when the import is static?

I would think this would work but it doesn't:

import static com.example.MyClass.myStaticMethod;  someStream.map(myStaticMethod); //does not compile 

Why does this not work? Am I 'stuck' with using the first example or are there other solutions.

Answer 1

Let's look at the relevant part of the Java Language Specification, 15.13. Method Reference Expressions.

It lists the following ways to a create method reference:

MethodReference:   ExpressionName :: [TypeArguments] Identifier    ReferenceType :: [TypeArguments] Identifier    Primary :: [TypeArguments] Identifier    super :: [TypeArguments] Identifier    TypeName . super :: [TypeArguments] Identifier    ClassType :: [TypeArguments] new    ArrayType :: new 

Note that all of them include a :: token.

Since the argument to someStream.map(myStaticMethod) does not include ::, it is not a valid method reference.

This suggests that you do need to import MyClass (perhaps in addition to the static import, if that's your preference) and refer to the method as MyClass::myStaticMethod.