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40. Properly encode relationships in constant definitions

The definitions of constant expressions should be related exactly when the values they express are also related.

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 = 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;

Bibliography

[JLS 2013]

§4.12.4, “final Variables”

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