src/main/java/io/reactivex/Single.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<Boolean> contains(Object value) {
        return contains(value, ObjectHelper.equalsPredicate());
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<Boolean> contains(Object value) {
        return contains(value, ObjectHelper.equalsPredicate());
    }
Signals true if the current Single signals a success value that is Object-equals with the value
provided.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code contains} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param value the value to compare against the success value of this Single
@return the new Single instance
@since 2.0