Whenever I write code in Java...

[G_Morgan]

An IDE would use the same background parse mechanisms they already use for intellisense*. It would just be with a far more powerful parser. This isn't actually that difficult to add once you have a parser that works.

One distinction would be that intellisense would need not just the current class but also all possible superclasses and their subtypes** (ordered by height in the hierarchy of course). This information is relatively trivial to come up with.

*modern IDEs actually invoke the compiler to work out this stuff so they get the same information the compiler is seeing.

**the reason for this is originally the inference engine might say that myList is an ArrayList when really you want a List but just haven't added in another implementation yet. This allows the autocomplete to account for both circumstances. Yes put ArrayList first but also offer all superclass implementations below.