Calling a protected static Java method from Scala

8
votes

I have a library here with some Java classes. One class has some protected static methods, which I realize is sorta an OOP no-no but I can't change its code. Assuming I have a Scala class that subclasses the aforementioned Java class, how can I call its protected static members?

1
scalascala-java-interop
Is it not an option to make a Java subclass that calls the super class method? You could then make your Java class accessible to Scala. – Madoc
Ah, yes, I guess I could go that route. Thanks. Seems a bit odd that it's not possible directly though! – J Cooper
Maybe it's possible more directly in Scala, I don't know. That's why I posted this as a comment and not as an answer. Obviously, a "super" call cannot work because Scala has no static inheritance. Maybe you can make a Scala object that extends the class in question and then call "LibraryClassName.staticMethodName(...)", thereby avoiding to use "super"? I'm not sure if this would work. – Madoc

1 Answers

21
votes

See Frequently Asked Questions - Java Interoperability:

This is a known limitation of Scala: there is no notion of 'static' members in Scala. Instead, Scala treats static members of class Y as members of the singleton object Y (the companion object of class Y). When inheriting from this class, one can access only protected members of class Y but cannot access protected members of object Y.

There's no way Scala can simulate static protected without impairing the integrity of Scala's object model in a fundamental way, so this is not going to change. To work around this limitation, one has to create an implementation of the enclosing class with Java code which encapsulates all accesses to the protected static inner class.

See ticket #1806 for more information and a concrete example of the limitation and its workaround.