CODEWITHSUNDEEP
rx-java
Marc
Marc

Reputation: 219

Observable.defer vs Observable.just

http://blog.danlew.net/2015/07/23/deferring-observable-code-until-subscription-in-rxjava/ discusses creating observables using Observable.just, Observable.create, and Observable.defer

Let's say I have this:

List<File> fileIOFunction() {
    // does some file io operations
}

OBSERVABLE.subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())

What thread do the file io operations run on if OBSERVABLE is:

Observable.create(
                new Observable.OnSubscribe<List<File>>() {
                    @Override
                    public void call(Subscriber<? super List<File>> 
                                     subscriber) {
                        subscriber.onNext(fileIOFunction());
                 }

If OBSERVABLE is Observable.just(fileIOFunction())

If OBSERVABLE is 

Observable.defer(new Func0<Observable<List<File>>>() {
                @Override
                public Observable<List<File>> call() { 
                    return Observable.just(fileIOFunction());
                });

Upvotes: 0

Views: 1261

Answers (1)

Sergej Isbrecht
Sergej Isbrecht

Reputation: 4012

For just it will run on calling thread, because fileIOFunction() will be invoked eagerly. Defer and Create will run on Schedulers.io() due to subscribeOn and will switch to AndroidSchedulers.mainThread() due to observeOn (switch thread). Create and Defer are lazy.

Upvotes: 1

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