If a variable is set to null, this means it points to a null object on the heap.


null is an object


null is a reference pointing to no object

Here is what's right.

null is a value that does not point to anything. All other reference values point to some heap object, but null means that it does not point anywhere.

Where could this misconception come from?

Students may have prior exposure to languages like Smalltalk or Self, where every value is an object. In a language like Self, nil indeed is an object. (Self’s nil takes the same role as Java’s null.)

How can you build on this misconception?

This misconception provides a good opportunity to introduce the dangers of null, as explained by its inventor: Turing Award winner Tony Hoare introduced the idea of a Null reference in ALGOL W back in 1965 “simply because it was so easy to implement”. In his QCon London 2009 presentation he talks about that decision and considers it his “billion-dollar mistake”.

The “Null Object” or “Sentinel Object” idioms, or the Nothing case of a Maybe or Optional monad, all represent the absence of a value with a special object, and represent a way to fix Hoare’s billion-dollar mistake. Thus, it’s really not that crazy an idea to consider null to be a special, singleton, object.

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