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Noncompliant Code Example

In this noncompliant code example, the @SuppressWarnings annotation's scope encompasses the whole class. This is dangerous as all unchecked warnings within the class will be suppressed. Oversights of this nature can lead to a ClassCastException at runtime.

@SuppressWarnings("unchecked") class Legacy {
  Set s = new HashSet();
  public final void doLogic(int a,char c) {
    s.add(a);
    s.add(c); // typeType unsafe operation, ignored
  }
}

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class Legacy {
  @SuppressWarnings("unchecked")  Set s = new HashSet();
  public final void doLogic(int a,char c) {
    s.add(a); //produces Produces unchecked warning
    s.add(c); // producesProduces unchecked warning
  }
}

Noncompliant Code Example

This noncompliant code example is from the implementation of java.util.ArrayList. When the class is compiled, it emits an unchecked cast warning, as shown. As the return statement is not a declaration, the Java Language Specification [JLS 05] makes it impossible to suppress the warning trivially. Consequently, the @SuppressWarnings is used over method scope. This can cause issues when some functionality that performs type-unsafe operations is added to the method at a later date. [Bloch 08]

@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
  if (a.length < size)
    return (T[]) Arrays.copyOf(elements, size, a.getClass()); // producesProduces unchecked warning
 // ...
}

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When it is impossible to use the @SuppressWarnings annotation, such as in the case of the preceding noncompliant code example, declare a new variable to hold the return value and adorn it with the @SuppressWarings @SuppressWarnings annotation.

// ...
@SuppressWarnings("unchecked") T[] result =
(T[]) Arrays.copyOf(elements, size, a.getClass());
return result;
// ...

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