4 DCL03-J. Properly encode relationships in constant definitions

The definitions of two constant expressions should be related when, and only when, the values they express are also related.

4.1 Noncompliant Code Example

In this noncompliant code example, OUT_STR_LEN must always be exactly two 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 = 12;

4.2 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;

4.3 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 ADULT_AGE = 18;
public static final int ALCOHOL_AGE = ADULT_AGE + 3;

A programmer performing routine maintenance may modify the definition for ADULT_AGE but fail to recognize the resulting change in the definition for ALCOHOL_AGE.

4.4 Compliant Solution

In this compliant solution, the definitions reflect the independence of the two constants.

public static final int ADULT_AGE = 18;
public static final int ALCOHOL_AGE = 21;

4.5 Risk Assessment

Failure to properly encode relationships in constant declarations can lead to unexpected values and can complicate maintenance.

4.6 Automated Detection

Automated detection is not currently feasible.

4.7 Related Guidelines

C Secure Coding Standard: DCL08-C. Properly encode relationships in constant definitions

C++ Secure Coding Standard: DCL08-CPP. Properly encode relationships in constant definitions

4.9 Bibliography

[[JLS 2005]] § 4.12.4, "final Variables"

DCL02-J. Use meaningful symbolic constants to represent literal values in program logic      01. Declarations and Initialization (DCL)      DCL04-J. Do not apply public final to constants whose value might change