Eclipse is one of the best java editing environments though, in terms of understanding java and not just editing text. Yes it's fidgety and ram hungry, but using it is a significant improvement over vim etc strictly in terms of my productivity. Though it may only really demonstrate value on larger apis; if you can keep most of an api in your head, ie it's a very small java project using few external libs, it may not do much for you.
And I just bought 16GB of ram for my macbook for $150; it's from crucial which I've had good experiences with but it's as expensive as it gets for 2x8GB. So that's a pretty trivial expense for your development environment: $75 a year.
You and the OP are comparing apples and oranges. VIM is an editor, Eclipse is an IDE. You can have your cake and eat it too [1]. Eclipse is a good cross platform IDE yes, but throwing more RAM at it won't make it feel natural and native to the platform.
And I just bought 16GB of ram for my macbook for $150; it's from crucial which I've had good experiences with but it's as expensive as it gets for 2x8GB. So that's a pretty trivial expense for your development environment: $75 a year.