What is the difference between '&' and ',' in Java generics?
<T extends MyClass & Serializable>
This asserts that the single type parameter T must extend MyClass and must be Serializable.
<T extends MyClass , Serializable>
This declares two type parameters, one called T (which must extend MyClass) and one called Serializable (which hides java.io.Serializable — this is probably what the warning was about).