Question about generics - the type being deduced does not match the declared boundaries (s)

Question

We currently have one class that will not compile with openjdk 6. The following abbreviated class reproduces this error:

public class Copy implements ICopy { public <A,B extends List<A>,C extends Map<A,B>> A method(A a, B b) { A something = null; return something; } @Override public <A,B extends List<A>> A method2(A a, B b) { return method(a,b); } } 

The interface is simple, it just shows that we cannot change the signature of method2 :

 public interface ICopy { public <A,B extends List<A>> A method2(A a, B b); } 

It compiles with versions of oracles java and openjdk 7 - but does not work with openjdk 6, and, unfortunately, this version, which we must use to compile the (source) code.

Error message

 Copy.java:15: invalid inferred types for C; inferred type does not conform to declared bound(s) inferred: java.util.Map<A,B> bound(s): java.util.Map<A,B> return method(a,b); ^ 

All I need are some ideas on how to change the implementation of method2 so that it method2 . I would not even bother with compiler warnings ...

Answer 1

I would try to explicitly specify the boundaries, for example:

 return this.<A,B,Map<A,B>>method(a,b); 

However, in general, I do not see the need for a type C parameter at all. None of the arguments to method or its reference reference type are C , so if you could change the signature of the method , I would just completely omit this type parameter.