The Art of Coding
One of the greatest challenges of coding is being able to understand it. Skill in coding is being able to understand the problem well enough to create a solution (otherwise known as coding). Great Skill is being able to write a solution so that someone else (including the future you) can read and understand what it is they are looking at. This concept isn't new, but yet we seem to be either challenged with the concept... or distracted. Even back in 1952 (yes 1952!!), in the computer history archive a set of lecture notes which in them states: "It is quite difficult to decipher coded programs even with notes and even if you yourself made the program several months ago." It also states: "I think the answer is simple: to make it easy one must make coding comprehensible". Well said!
The Point of Constants
One area that seems to be a constant :) struggle is constants. There are at least a couple of justifications for using constants I can think of: 1) a point of reference for tools (autocomplete with intellisense in IDEs and refactoring), 2) A common holder of value for which if it changes will be realized across the system. The main point of a constant isn't DRY or reuse... a common point of confusion for some reason.
IMO the stronger argument is point 2. if you were coding in VI or emacs, point 1 may not be of value, but point 2 certainly would be. If you name the reference of a constant the same name as the value of the constant... then you lose any the value of point 2.
It must also be said that constants, although they add value, they make code less readable (see examples below). If your constants have no value, they don't achieve points 1 and 2, then they need to be whacked!
Examples of Losing with Constants
This is real production code... some variables changed to obscure identify.
// example 1 Really?? where does this end?
String EMPTY_STRING = "";
// this isn't readable... it takes minutes (instead of seconds) to understand its value
// example 2
String ADVERTISE_PROPERTY_PREFIX = OUR_PROPERTY_PREFIX + "advertise.";
String ADVERTISE_TRADER_ADDRESS_PROPERTY = ADVERTISE_PROPERTY_PREFIX + "host";
String ADVERTISE_CONTEXT_PROPERTY = ADVERTISE_PROPERTY_PREFIX + "context";
String ADVERTISE_TYPE_PROPERTY = ADVERTISE_PROPERTY_PREFIX + "type";
// example 3
// here's a common one
static final String TABLE_NAME = "email";
// Column names for all the fields in the email table
static final String ID = TABLE_NAME + ".email_id";
static final String CUSTOMER_ID = TABLE_NAME + ".customer_id";
static final String ADDRESS = TABLE_NAME + ".address";
static final String FIELDS = ID + ", " + CUSTOMER_ID + ", " + ADDRESS + ", " + CREATED_BY + ", " + LAST_MOD_BY
+ ", " + CREATE_DATE + ", " + LAST_MOD_DATE + ", " + TERM_DATE + ", " + WEB_USER_ID;
// List of fields names with formatting used for select statements
static final String SELECT_FIELDS = ID + ", " + CUSTOMER_ID + ", " + ADDRESS + ", " + CREATED_BY + ", "
+ LAST_MOD_BY + ", " + "TO_CHAR(" + CREATE_DATE + ",'" + DATE_TIME_FORMAT + "')," + "TO_CHAR("
+ LAST_MOD_DATE + ",'" + DATE_TIME_FORMAT + "')," + "TO_CHAR(" + TERM_DATE + ",'" + DATE_TIME_FORMAT
+ "')," + WEB_USER_ID;
// SQL used to create a new EMAIL record
static final String CREATE_SQL = "INSERT INTO " + TABLE_NAME + " (" + FIELDS
+ ") VALUES (?,?,?,?,?,SYSDATE,SYSDATE,NULL,?)";
// SQL used to retrieve an email record by id
static final String RETRIEVE_BY_ID_SQL = "SELECT " + SELECT_FIELDS + " FROM " + TABLE_NAME + " WHERE " + TERM_DATE
+ " IS NULL AND " + ID + "=?";
For example 1... where does it end? would you create a constant A = "A"? When can EMPTY_STRING not be an empty string or ""? In this case, we get no value and less readability.
Example 2 is the chaining of constants, commonly found when there are a large number of property values being retrieved from a file or sys env. While not as bad as example 1, it is less readable. Having a prefix constant may be of value, but rarely is the chaining of constants of value. It isn't worth trading the potential for a company name change or something similar for readability. Or put another way, it isn't worth trading something that is unlikely to happen for something else which is more likely to be needed (that being the readability of the code)
Example 3 I see all the time... argghhhhh... please... just stop!
Examples of good constants would include, urls and database connections strings or a project defined standard date format.
May your constants always be final!