javaoption-typenon-nullable

Is it possible to document that return value is not null with Java Optional?

Is it possible to document that return value is not null with Java Optional?

Most tools and frameworks care only about arguments but I'd like to express in type that return value is not null (instead of doing that in JavaDoc).

UPDATE Looks like you can agree with team to use Optional as return value if you want to express possible null and direct object when it is definitely not null:

public Optional<Job> getJob() {  ... }
public Job extractJob(NonNullJobHolder<Job> holder) { ... }
Solution

  • I don't know why you're under the impression that most of them apply only to parameters.

    org.eclipse.jdt.annotation.NonNull

    @Documented
@Retention(value=CLASS)
@Target(value={FIELD,METHOD,PARAMETER,LOCAL_VARIABLE})
public @interface NonNull

    org.jetbrains.annotations.NotNull

    The @NotNull annotation is, actually, an explicit contract declaring that:

    • A method should not return null
    • Variables (fields, local variables, and parameters) cannot hold a null value

    Usage:

    intellij @NotNull

    javax.validation.constraints.NotNull

    @Target(value={METHOD,FIELD,ANNOTATION_TYPE,CONSTRUCTOR,PARAMETER})
@Retention(value=RUNTIME)
@Documented
@Constraint(validatedBy={})
public @interface NotNull

    javax.annotation.Nonnull

    @Documented
@TypeQualifier
@Retention(value=RUNTIME)
public @interface Nonnull

    Usage:

    javax @Nonnull

    So feel free to use any one of these four on your method.