RxJava 2.x 几个可观察者在有、无、错误三情况下的执行迥

Flowable: onSubscribe oNext* (onError | onComplete)?
Observable: onSubscribe oNext* (onError | onComplete)?
Single: onSubscribe (onSuccess | onError)?
Completable: onSubscribe (onError | onComplete)?
Maybe: onSubscribe (onSuccess | onError | onComplete)?

Maybe is a hybrid of Single and Completable where only one of the | -ed method is called.

参考链接1: issues/4534
参考链接2: reactive-streams-jvm

在Rxjava 1.x (无RSS规范时代)，只有Observable、Single、Completable、Maybe这几个可观察者，Single、Completable、Maybe从Observable衍生而来. 规范出来后Rxjava 2.x添加了Flowable可观察支持了RSS规范