Package org.checkerframework.framework.qual

Annotation Type Covariant

  • @Documented
@Retention(RUNTIME)
@Target(TYPE)
public @interface Covariant
    A marker annotation, written on a class declaration, that signifies that one or more of the class's type parameters can be treated covariantly. For example, if MyClass has a single type parameter that is treated covariantly, and if B is a subtype of A, then SomeClass<B> is a subtype of SomeClass<A>.

    Ordinarily, Java treats type parameters invariantly: SomeClass<B> is unrelated to (neither a subtype nor a supertype of) SomeClass<A>.

    It is only safe to mark a type parameter as covariant if clients use the type parameter in a read-only way: clients read values of that type but never modify them.

    This property is not checked; the @Covariant is simply trusted.

    Here is an example use: 

    @Covariant(0)
 public interface Iterator<E extends @Nullable Object> { ... }
    See the Checker Framework Manual:
    Covariant type parameters

    • Required Element Summary

      Required Elements 
      Modifier and Type Required Element Description
      int[] value
      The zero-based indices of the type parameters that should be treated covariantly.

    • Element Detail

      • value

        int[] value
        The zero-based indices of the type parameters that should be treated covariantly.