Method just

src/main/java/io/reactivex/rxjava3/core/Single.java:1239–1245

Returns a Single that emits a specified item. To convert any object into a Single that emits that object, pass that object into the just met

(T item)

     * @see <a href="http://reactivex.io/documentation/operators/just.html">ReactiveX operators documentation: Just</a>
     */
    @CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    @NonNull
    public static <@NonNull T> Single<T> just(T item) {
        Objects.requireNonNull(item, "item is null");
        return RxJavaPlugins.onAssembly(new SingleJust<>(item));
    }

    /**
     * Merges an {@link Iterable} sequence of {@link SingleSource} instances into a single {@link Flowable} sequence,