为什么Java collection . tolist()在返回类型中需要通配符类型占位符?

I've been doing some Java Streams manipulation, and of course it doesn't like my code and is refusing to provide useful error messages. (For reference, I have no problems whatsoever with C# and Linq, so I understand conceptually everything I'm trying to do.) So I started digging into adding the explicit generic types to every method in my code so I can find the source of the problem, as past experience tells me that this is a successful path forward.I've been doing some Java Streams manipulation,