Method Reference. Cannot make a static reference to the non-static method

Question

Can someone explain to me,
why passing a non-static method-reference to method File::isHidden is ok,
but passing method reference to a non-static met

Answer 1

Method references to non-static methods require an instance to operate on.

In the case of the listFiles method, the argument is a FileFilter with accept(File file). As you operate on an instance (the argument), you can refer to its instance methods:

listFiles(File::isHidden)

which is shorthand for

listFiles(f -> f.isHidden())

Now why can't you use test(MyCass::mymethod)? Because you simply don't have an instance of MyCass to operate on.

You can however create an instance, and then pass a method reference to your instance method:

MyCass myCass = new MyCass(); // the instance
test(myCass::mymethod); // pass a non-static method reference

or

test(new MyCass()::mymethod);

Edit: MyCass would need to be declared static (static class MyCass) in order to be accessible from the main method.