Java naming convention for static final variables

Question

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• Should a “static final Logger” be declared in UPPER-CASE? 10 answers

there is a rule which says:

Names representing constants (final variables) must be all uppercase using underscore to separate words (taken from http://geosoft.no/development/javastyle.html)

that works fine for primitive types like int or strings:

private static final int MAX_COUNT = 10;

But what's about non primitive types? In most cases I've seen the following:

private static final Logger log = Logger.getLogger(MyClass.class);

or in singletons, where instance variable is not in upper case.

The question is what is the right way to declare those types of variables (like log and instance)?

Answer 1

The language doesn't care. What's important is to follow the established styles and conventions of the project you're working on, such that other maintainers (or you five months from now) have the best possible chance of not being confused.

I think an all-uppercase name for a mutable object would certainly confuse me, even if the reference to that object happened to be stored in a static final variable.

Answer 2

Well that's a very interesting question. I would divide the two constants in your question according to their type. int MAX_COUNT is a constant of primitive type while Logger log is a non-primitive type.

When we are making use of a constant of a primitive types, we are mutating the constant only once in our code public static final in MAX_COUNT = 10 and we are just accessing the value of the constant elsewhere for(int i = 0; i<MAX_COUNT; i++). This is the reason we are comfortable with using this convention.

While in the case of non-primitive types, although, we initialize the constant in only one place private static final Logger log = Logger.getLogger(MyClass.class);, we are expected to mutate or call a method on this constant elsewhere log.debug("Problem"). We guys don't like to put a dot operator after the capital characters. After all we have to put a function name after the dot operator which is surely going to be a camel-case name. That's why LOG.debug("Problem") would look awkward.

Same is the case with String types. We are usually not mutating or calling a method on a String constant in our code and that's why we use the capital naming convention for a String type object.

Answer 3

Don't live fanatically with the conventions that SUN have med up, do whats feel right to you and your team.

For example this is how eclipse do it, breaking the convention. Try adding implements Serializable and eclipse will ask to generate this line for you.

Update: There were special cases that was excluded didn't know that. I however withholds to do what you and your team seems fit.

Answer 4

A constant reference to an object is not a constant, it's just a constant reference to an object.

private static final is not what defines something to be a constant or not. It's just the Java way to define a constant, but it doesn't mean that every private static final declaration was put there to define a constant.

When I write private static final Logger I'm not trying to define a constant, I'm just trying to define a reference to an object that is private (that it is not accessible from other classes), static (that it is a class level variable, no instance needed) and final (that can only be assigned once). If it happens to coincide with the way Java expects you to declare a constant, well, bad luck, but it doesn't make it a constant. I don't care what the compiler, sonar, or any Java guru says. A constant value, like MILLISECONDS_IN_A_SECOND = 1000 is one thing, and a constant reference to an object is another.

Gold is known to shine, but not everything that shines is gold.

Answer 5

That's still a constant. See the JLS for more information regarding the naming convention for constants. But in reality, it's all a matter of preference.

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The names of constants in interface types should be, and final variables of class types may conventionally be, a sequence of one or more words, acronyms, or abbreviations, all uppercase, with components separated by underscore "_" characters. Constant names should be descriptive and not unnecessarily abbreviated. Conventionally they may be any appropriate part of speech. Examples of names for constants include MIN_VALUE, MAX_VALUE, MIN_RADIX, and MAX_RADIX of the class Character.

A group of constants that represent alternative values of a set, or, less frequently, masking bits in an integer value, are sometimes usefully specified with a common acronym as a name prefix, as in:

interface ProcessStates {
  int PS_RUNNING = 0;
  int PS_SUSPENDED = 1;
}

Obscuring involving constant names is rare:

• Constant names normally have no lowercase letters, so they will not normally obscure names of packages or types, nor will they normally shadow fields, whose names typically contain at least one lowercase letter.
• Constant names cannot obscure method names, because they are distinguished syntactically.

Answer 6

These variables are constants, i.e. private static final whether they're named in all caps or not. The all-caps convention simply makes it more obvious that these variables are meant to be constants, but it isn't required. I've seen

private static final Logger log = Logger.getLogger(MyClass.class);

in lowercase before, and I'm fine with it because I know to only use the logger to log messages, but it does violate the convention. You could argue that naming it log is a sub-convention, I suppose. But in general, naming constants in uppercase isn't the One Right Way, but it is The Best Way.