Packages 
Package Description
io.reactivex
Base reactive classes: Flowable, Observable, Single and Completable; base reactive consumers; other common base interfaces.
io.reactivex.annotations
Annotations for indicating experimental and beta operators, classes, methods, types or fields.
io.reactivex.disposables
Default implementations for Disposable-based resource management (Disposable container types) and utility classes to construct Disposables from callbacks and other types.
io.reactivex.exceptions
Exception handling utilities, safe subscriber exception classes, lifecycle exception classes.
io.reactivex.flowables
Classes supporting the Flowable base reactive class: connectable and grouped flowables.
io.reactivex.functions
Functional interfaces of functions and actions of arity 0 to 9 and related utility classes.
io.reactivex.observables
Classes supporting the Observable base reactive class: connectable and grouped observables.
io.reactivex.observers
Default wrappers and implementations for Observer-based consumer classes and interfaces; utility classes for creating them from callbacks.
io.reactivex.parallel
Base type for the parallel type offering a sub-DSL for working with Flowable items in parallel.
io.reactivex.plugins
Callback types and a central plugin handler class to hook into the lifecycle of the base reactive types and schedulers.
io.reactivex.processors
Classes extending the Flowable base reactive class and implementing the Subscriber interface at the same time (aka hot Flowables).
io.reactivex.schedulers
Scheduler implementations, value+time record class and the standard factory class to return standard RxJava schedulers or wrap any Executor-based (thread pool) instances.
io.reactivex.subjects
Classes extending the Observable base reactive class and implementing the Observer interface at the same time (aka hot Observables).
io.reactivex.subscribers
Default wrappers and implementations for Subscriber-based consumer classes and interfaces; utility classes for creating them from callbacks.