Java generics compile in Eclipse, but not in javac

Question

I had to discover I have Java code in my project, which compiles and runs fine in Eclipse, but throws a compilation error in javac.

A self-contained snippet:

Answer 1

You are right. This problem indeed exists. Eclipse does not use javac. It uses its own compiler.

Actually javac is "right". Generics are erasures. Type S is not included into your byte code, so jvm does not have enough information about the return type at runtime. To solve the problem change the method prototype as following:

public static Set covariantSet(Set set, Class returnType)

Now the return type is passed to the method at runtime and compiler should not complain.