Can "this" ever be null in Java?
No it can't. If you're using this, then you're in the instance so this isn't null.
The JLS says :
When used as a primary expression, the keyword this denotes a value that is a reference to the object for which the instance method was invoked (§15.12), or to the object being constructed.
If you invoked a method from an object, then the object exists or you would have a NullPointerException before (or it's a static method but then, you can't use this in it).
Resources :
- JLS -
thiskeyword
It's like asking yourself "Am I alive?" this can never be null