Learning RxJava - Second Edition

A hot Observable

You just learned about the cold Observable, which works much like a music CD. A hot Observable is more like a radio station. It broadcasts the same emissions to all observers at the same time. If an Observer subscribes to a hot Observable, receives some emissions, and then another Observer subscribes later, that second Observer will have missed those emissions. Just like a radio station, if you tune in too late, you will have missed that song.

Logically, a hot Observable often represent events rather than finite datasets. The events can carry data with them, but there is a time-sensitive component, and late subscribers can miss previously emitted data.

For instance, a JavaFX or Android UI event can be represented as a hot ...