How To Use

# Hello World!

Requisite first example which creates an Observable from a list of Strings, subscribes to the Observable with a function that will print "Hello [arg]!" for each string.

This example is given first in Java and then other languages to provide comparison.

Subsequent examples will use a mixture of languages all of which can be found in the rxjava-examples submodule.

Java

public static void hello(String... names) {
    Observable.toObservable(names).subscribe(new Action1<String>() {

        @Override
        public void call(String s) {
            System.out.println("Hello " + s + "!");
        }

    });
}

hello("Ben", "George");
Hello Ben!
Hello George!

Groovy

def hello(String[] names) {
    Observable.toObservable(names)
        .subscribe({ println "Hello " + it + "!"})
}

hello("Ben", "George")
Hello Ben!
Hello George!

Clojure

(defn hello
  [&rest]
  (-> (Observable/toObservable &rest)
    (.subscribe #(println (str "Hello " % "!")))))

(hello ["Ben" "George"])
Hello Ben!
Hello George!

Creating Observable Sequences

An Observable sequence originates from two sources, an existing data structure or an Observable implementation which synchronously or asynchronously executes and passes data via onNext().

Existing Data

The Observable toObservable, from and just methods allow converting any object, list or array of objects into an observable sequence:

Observable<Integer> o = Observable.toObservable(1, 2, 3, 4, 5, 6);

Observable<String> o = Observable.from("a", "b", "c");

def list = [5, 6, 7, 8]
Observable<Integer> o = Observable.toObservable(list);

Observable<String> o = Observable.just("one object");

These sequences will synchronously invoke onNext() on an Observer when subscribed to for each object and then call onCompleted().

Observable Implementation

Asynchronous IO or computational operations or "infinite" streams of data can be implemented using the Observable class.

This can be done either by extending the Observable class or by using the Observable.create() factory method.

An observable sequence can

• from existing data
• as an API for async
  • Give control of blocking/non-blocking to API
• blocking
• non-blocking

More information can be found on the Observable and Creation Operators pages.

Composition

Error Handling

OnError subscribe, resume next, delay