The definitions of two constant expressions should be related only when the values they express are also related.
Noncompliant Code Example
In this noncompliant code example, OUT_STR_LEN must always be exactly 2 greater than IN_STR_LEN. These definitions fail to reflect this requirement:
public static final int IN_STR_LEN = 18; public static final int OUT_STR_LEN = 20;
Compliant Solution
In this compliant solution, the relationship between the two values is represented in the definitions:
public static final int IN_STR_LEN = 18; public static final int OUT_STR_LEN = IN_STR_LEN + 2;
Noncompliant Code Example
In this noncompliant code example, there appears to be an underlying relationship between the two constants where none exists.
public static final int VOTING_AGE = 18; public static final int ALCOHOL_AGE = VOTING_AGE + 3;
A programmer performing routine maintenance may modify the definition for VOTING_AGE but fail to recognize the resulting change in the definition for ALCOHOL_AGE.
Compliant Solution
In this compliant solution, the definitions reflect the independence of the two constants.
public static final int VOTING_AGE = 18; public static final int ALCOHOL_AGE = 21;
Applicability
Failure to properly encode relationships in constant declarations can lead to unexpected values and can complicate maintenance.
Bibliography
[JLS 2011] §4.12.4, "final Variables"