Ensure the following option is enabled: Window | Preferences | Java | Editor | Content Assist | Enable auto activation. Set the delay to ms.
Then create a Groovy class and try to write a range (like (1..2)) in a method body, by typing each character one by one. You'll end up with: (1.TYPE.2)
This is because after the first dot content assist starts and the second dot performs as a trigger character that causes the first suggestion (TYPE constant defined in Class) to be inserted.

Hint: maybe . should not be treated as a trigger character when following another ..

Note 1: why content assist talks about Void.TYPE instead of Integer.TYPE (like F3 does, after you type it)?
Note 2: maybe I am missing something obvious, but why this constant (which is defined in Class class) is available as a static reference access in an instance variable?