# RxJava Observable to Single

DevFeed: [RxJava Observable to Single](<https://devfeed.tech/articles/rxjava-observable-to-single-38612.md>)

Original publisher: [Read original article](<https://krossovochkin.com/posts/2019_05_27_rxjava_observable_to_single/>)

Published: 2019-05-27T00:00:00Z

Content type: tutorial

Language: en

Sources: [Vasya Drobushkov](<https://devfeed.tech/sources/vasya-drobushkov.md>)

Topics: [RxJava](<https://devfeed.tech/topics/rxjava.md>), [implementation](<https://devfeed.tech/topics/implementation.md>)

Tags: [implementation](<https://devfeed.tech/tags/implementation.md>), [observable](<https://devfeed.tech/tags/observable.md>), [rxjava](<https://devfeed.tech/tags/rxjava.md>), [stream](<https://devfeed.tech/tags/stream.md>)

## AI overview

This tutorial explains how to transform RxJava Observable instances into Single instances. It compares operators such as single, singleOrError, Single.fromObservable, elementAt, and first, and describes how their underlying strategy handles emitted values, completion, and errors.

## Source excerpt

Transforming Single to Observable is simple, as Single satisfies Observable's contract. Just call single.toObservable() and you're good. But transforming Observable to Single is not that simple: if it happens that Observable emits exactly one value and completes (or terminates with error without emitting values) then it is pretty straightforward, otherwise one need to set up some additional rules. In RxJava there are a number of operators for transforming Observable to Single: