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Is there a purpose to have a constant for null?

I recently saw something in some code that made me wonder if there was actually some kind of optimization or performance impact. This was the line in the constants file:

public static final Object NULL = null;

Then, throughout the code, instead of using the keyword explicitly, null

it will be referenced Constants.NULL

.

I've seen such a thing before with something like:

public static final String EMPTY_STRING = "";

... and it seems to make at least some sense if it is an attempt to avoid creating many duplicate instances ""

. But does it really matter with null

, since it isn't really any object? Is there something I am missing?

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3 answers


I don't think defining and using NULL

this way is more than adding noise. Perhaps whoever wrote this code came from a C ++ background and preferred the more familiar NULL

over NULL

.

The second example is also questionable, since using ""

multiple times will not result in a separate object String

created for each use. To quote the JLS :



In addition, the string literal always refers to the same instance of the class String

. This is because string literals - or more generally - strings that are constant expression values ​​(§15.28) - are "interned" to exchange unique instances using a method String.intern

.

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Nothing makes sense. Using it ""

in multiple places in your code does not create multiple instances of the String object. Unless you explicitly call new String("");

, the JVM just creates a row pool and references one instance of each specific row.



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Doesn't matter in memory footprint due to the concept of string pooling in java, and also makes the code messier by using the constant NULL instead of null or EMPTY_STRING instead of "".

Both are self-explanatory, so there is no need to create a naming constant for them.

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