Method just

src/main/java/io/reactivex/rxjava3/core/Observable.java:2645–2651

Returns an Observable that signals the given (constant reference) item and then completes. Note that the item is taken and re-emitted as is and not computed by a

(@NonNull T item)

     * @see #fromIterable(Iterable)
     */
    @CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <@NonNull T> Observable<T> just(@NonNull T item) {
        Objects.requireNonNull(item, "item is null");
        return RxJavaPlugins.onAssembly(new ObservableJust<>(item));
    }

    /**
     * Converts two items into an {@code Observable} that emits those items.