EXP10-J. Avoid side-effects in assertions

The assert() statement is a convenient mechanism for incorporating diagnostic tests in code. Expressions used with the standard assert statement should avoid side-effects. Typically, the behavior of the assert statement depends on the status of a runtime property. When enabled, the assert statement is designed to evaluate its expression argument and throw an AssertionError if the result of the expression is false. When disabled, assert is defined to be a no-operation. Consequently, any side-effects resulting from evaluation of the expression in the assertion are lost when assertions are disabled.

Noncompliant Code Example

This noncompliant code example demonstrates an action being carried out in an assertion. The idea is to delete all the null names from the list; however, the boolean expression is unexpectedly not evaluated when assertions are disabled.

void process(int index) {
  assert names.remove(null); // side-effect 
  // ...
}

Compliant Solution

Avoid the possibility of side-effects in assertions. This can be achieved by decoupling the boolean expression from the assertion.

void process(int index) {
  boolean nullsRemoved = names.remove(null);
  assert nullsRemoved; // no side-effect 
  // ... 
}

Risk Assessment

Side-effects in assertions can lead to differences in program behavior that depend on whether assertions are enabled.

Guideline	Severity	Likelihood	Remediation Cost	Priority	Level
EXP10-J	low	unlikely	low	P3	L3

Automated Detection

Automated detection of assertion operands that contain locally-visible side-effects is straightforward. Some analyses could require programmer assistance to determine which method invocations could contain side-effects.