Supported Annotations

This page documents the different code annotations that are supported by NullAway by default. Custom annotations can be supported for certain functionality via the command-line flags.

Nullability

NullAway treats any annotation whose simple (un-qualified) name is @Nullable as marking a parameter / return / field as nullable. Checker Framework's @NullableDecl is also supported.

Initialization

Any annotation whose simple (un-qualified) name is @Initializer is treated as marking a method as an initializer (see here for more information on initialization checking). We also support JUnit's @Before and @BeforeClass for marking initializers.

Contracts

NullAway has partial support for JetBrains @Contract annotations. Some examples:

public class NullnessChecker {

  @Contract("_, null -> true")
  static boolean isNull(boolean flag, @Nullable Object o) { return o == null; }

  @Contract("null -> false")
  static boolean isNonNull(@Nullable Object o) { return o != null; }

  @Contract("null -> fail")
  static void assertNonNull(@Nullable Object o) { if (o != null) throw new Error(); }

  @Contract("!null -> !null")
  static @Nullable Object id(@Nullable Object o) { return o; }
}

For now, the @Contract annotations are trusted, not checked. NullAway will warn if it sees a call to a method with a @Contract annotation it recognizes as invalid.

Not all possible clauses of @Contract annotations are fully parsed or supported by NullAway (e.g. @Contract("null, false -> fail; !null, true -> fail") will be ignored, since NullAway cannot reason about the runtime value of the second argument).