JAVA.STRUCT.SE.ASSERT : Assertion Contains Side Effects (Java)

Summary

An assertion checks a condition with side-effects.

If an assertion has side effects, the semantics of the program will change depending on whether or not assertions are enabled.

Side-effects are updates to heap memory, such as variable, field or array assignment operations. They are essential in object-oriented code. However, there are situations where side-effects are unexpected or suspicious and should be avoided. This checker identifies unexpected or suspicious side-effects.

Properties

WARNING_FILTER += discard class="Assertion Contains Side Effects (Java)"

Example

The assert statements in the following code fragment check expressions whose evaluations have side effects: each checked expression updates a variable or field.

public class AssertionsWithSideEffects {
  public void assert1() {
      Object obj = null;
      assert (obj = new Object()) != null;       // "Assertion Contains Side Effects (Java)" warning issued here
  }

  public void assert2() {
      assert (list = new ArrayList<>()) != null; // "Assertion Contains Side Effects (Java)" warning issued here
  }

  public void assert3() {
      assert counter++ > 17;                     // "Assertion Contains Side Effects (Java)" warning issued here
  }

  public List<String> list = new ArrayList<>();
  private static int counter;
}

There are generally two options for resolving a situation where an assertion contains a side effect: either remove the side effect entirely, or move it outside the assert statement. For example, method assert1() could be rewritten as follows.

public void assert1() {
    Object obj = new Object();
    assert obj != null;
}

Resolution

Check if the side-effect is actually wrong and avoid it, for instance by moving the expression with side-effect into a separate, isolated statement.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER