Question

I recently saw something in some code that made me curious if it was actually having some kind of optimization or performance impact. It was a line like this in a constants file:

public static final Object NULL = null;

Then, throughout the code, rather than explicitly using the null keyword, it would be referred to with Constants.NULL.

I’ve seen this kind of thing before with something like:

public static final String EMPTY_STRING = "";

… and that seemed to make at least a little bit of sense, if it’s an attempt to avoid creating lots of duplicate "" instances. But does it really make any difference with null, since it’s not actually any kind of object? Is there something I’m missing?

Answer 1

I don’t think that defining and using NULL in this manner does more than add noise. Perhaps whoever wrote that code came from a C++ background, and preferred the more familiar look of NULL over null.

The second example is also questionable, since using "" many times would not result in a separate String object created for every use. To quote the JLS:

Moreover, a string literal always refers to the same instance of class String. This is because string literals – or, more generally, strings that are the values of constant expressions (§15.28) – are “interned” so as to share unique instances, using the method String.intern.