Understanding wildcards in Java generics

Question

I\'m not sure why the last statement in the following code is illegal. Integer should be a subtype of ?, so why can\'t I assign it to b

Answer 1

The point is that b refers to a list of some type, but the compiler doesn't know what the type is, so it doesn't know whether or not it's valid to add an Integer to it. And a good thing too, given your example - you'd be adding an Integer to an object initially created to hold a list of strings. Sure, that information is lost at execution time in Java - but the compiler tries to keep you as safe as it can.

See the Java generics FAQ for a lot more information.