Should a “static final Logger” be declared in UPPE

Question

In Java, static final variables are constants and the convention is that they should be in upper-case. However, I have seen that most people declare loggers in lower-case which comes up as a violation in PMD.

e.g:

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

Just search googleor SO for "static final logger" and you will see this for yourself.

Should we be using LOGGER instead?

Answer 1

If you are using an automated tool to check your coding standards and it violates said standards then it or the standards should be fixed. If you're using an external standard, fix the code.

The convention in Sun Java is uppercase for public static constants. Obviously a logger is not constant, but represents a mutable thing ( otherwise there would be no point calling methods on it in the hope that something will happen ); there's no specific standard for non-constant final fields.

Answer 2

I personally think it looks really big in upper-case. Moreover, since it's a class that it's not directly related to the class behaviour, I don't see a major problem in using logger instead of LOGGER. But if you are going to be strictly pedantic, then use LOGGER.

Answer 3

Don't forget that PMD will respect a comment with

// NOPMD

in it. This will cause PMD to skip the line from its checks, this will allow you to choose whichever style you want.

Answer 4

To add more value to crunchdog's answer, The Java Coding Style Guide states this in paragraph 3.3 Field Naming

Names of fields being used as constants should be all upper-case, with underscores separating words. The following are considered to be constants:

1. All static final primitive types (Remember that all interface fields are inherently static final).
2. All static final object reference types that are never followed by "." (dot).
3. All static final arrays that are never followed by "[" (dot).

Examples:

MIN_VALUE, MAX_BUFFER_SIZE, OPTIONS_FILE_NAME

Following this convention, logger is a static final object reference as stated in point 2, but because it is followed by "." everytime you use it, it can not be considered as a constant and thus should be lower case.

Answer 5

I like Google's take on it (Google Java Style)

Every constant is a static final field, but not all static final fields are constants. Before choosing constant case, consider whether the field really feels like a constant. For example, if any of that instance's observable state can change, it is almost certainly not a constant. Merely intending to never mutate the object is generally not enough.

Examples:

// Constants
static final int NUMBER = 5;
static final ImmutableList<String> NAMES = ImmutableList.of("Ed", "Ann");
static final Joiner COMMA_JOINER = Joiner.on(',');  // because Joiner is immutable
static final SomeMutableType[] EMPTY_ARRAY = {};
enum SomeEnum { ENUM_CONSTANT }

// Not constants
static String nonFinal = "non-final";
final String nonStatic = "non-static";
static final Set<String> mutableCollection = new HashSet<String>();
static final ImmutableSet<SomeMutableType> mutableElements = ImmutableSet.of(mutable);
static final Logger logger = Logger.getLogger(MyClass.getName());
static final String[] nonEmptyArray = {"these", "can", "change"};

Answer 6

The logger reference is not a constant, but a final reference, and should NOT be in uppercase. A constant VALUE should be in uppercase.

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

private static final double MY_CONSTANT = 0.0;