Generic arguments for serializable collections

Question

i have a member like this in a serializable class:

private final Map<String, List<T>> categoryMap = Maps.newHashMap();

the class has the following type-bounds.

<T extends Serializable>

I use findbugs to check for mistakes in my code, and it shows me that member as "not (guaranteed to be) serializable".

Answer 1

Because your serializable class contains the following member

private final Map<String, List<T>> categoryMap

here T can be any class Foo, which isn't guaranteed to be Serializable and so the warning/suggestion/eye opener

If you are expecting it to be serializable in all the cases than make it

List<? extends Serializable>

and if you don't want to seralize that field at all simply mark transient