Skip to content
An RxJava extension for reactive collections
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.

Reactive Collections for RxJava

Build Status Maven Central

RxJavaCollections is a library which offers extensions for the RxJava 2.x library, in order to observe operations performed on standard Java collections such as List<E>.

This project is still under development and currently only offers support for the List<E> and Set<E> classes.

Getting started

In order to observe actions performed on a List<E>, you can wrap an object of that type as RxCollections.of(list). This new object of type ObservableList<E> has various methods which return an Observable<Indexed<E>> object. One such method is onAdded(), which returns an observable that emits a value whenever an element is added to the list. The value emitted is of type Indexed<E> and contains the element added, as well as the index it was added at in the list. These values can be obtained with getValue() and getIndex() respectively.

Memory management

Typically a Java developer does not have to worry about memory management. Java has a garbage collector which periodically frees objects from the memory which are no longer referenced. This does however become an important consideration when working with infinite observables (observables which never complete), which are returned by various methods in this library. When an object is involved in subscribing to such an observable, it will never be removed from the memory unless the subscription is terminated when it is no longer required. This can be achieved by calling the dispose() method on the Disposableobject which is returned by the subscribe() method.


Creating this library was motivated by the fact that RxJava does not come with built-in support for this type of reactive collections. The reason for this is that collections like these are more akin to imperative programming, rather than the pure reactive methodology adopted by the ReactiveX framework on which RxJava is based.

In an imperative language such as Java, it can be beneficial to mix both the imperative and reactive strategies, especially when dealing with user interfaces. A possible downside of both the ReactFX and RXJavaFX, depending on the project they are used on, is that they have a fixed dependency on JavaFX. While both frameworks offer reactive collections (from JavaFX), similar to those available in this library, the dependency on JavaFX may inhibit the portability of projects to platforms where JavaFX is not available.


The reactive wrapper classes in this library incur a performance penalty, especially when performing operations with other collections, such as addAll(), because it will handle each element of these collections individually and emit them to the observables after each individual element has been handled.

To improve performance, the clear() method for the ArrayList<E> wrapper class ObservableArrayList<E> will remove and emit removals starting at the end of the list, rather than at the start.


Copyright (c) 2017, Frédéric Hannes.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

You can’t perform that action at this time.