RxJava Basics

Inspired by Grokking RxJava Tutorial check the code snippet below, in this post or check it here http://pastebin.com/9MR4k5E5

package org.rx.java.tutorial;

import java.util.ArrayList;
import java.util.List;

import rx.Observable;
import rx.Subscriber;
import rx.functions.Func1;

public class Main {

	// Check this tutorial:
	// http://blog.danlew.net/2014/09/15/grokking-rxjava-part-1/

	// Dependency for gradle project:
	// compile 'io.reactivex:rxjava:1.1.1'

	// ====================================================================

	// Key idea #1: Observable and Subscriber can do anything.

	// Key idea #2: The Observable and Subscriber are independent of the
	// transformational steps in between them.

	// Key idea #3: Operators let you do anything to the stream of data. The
	// only limit is yourself.

	// ====================================================================

	// Notes:
	// 1. onError() is called if an Exception is thrown at any time.
	// 2. The operators don't have to handle the Exception.
	// 3. You know when the Subscriber has finished receiving items.
	// 4. When you call Observable.subscribe(), it returns a Subscription.
	// 5. RxJava has awesome docs / marble diagrams inside code
	// 6. using unsubscribe will terminate wherever it is currently executing
	// code
	// 7. List of operators:
	// https://github.com/ReactiveX/RxJava/wiki/Alphabetical-List-of-Observable-Operators

	public static void main(String[] args) {

		// 1. verbose example
		Observable<String> myObservable = Observable.create(new Observable.OnSubscribe<String>() {
			public void call(Subscriber<? super String> sub) {
				sub.onNext(extracted());
				sub.onCompleted();
			}

			private String extracted() {
				return "1. Hello, world!";
			}
		});

		Subscriber<String> mySubscriber = new Subscriber<String>() {
			public void onCompleted() {
				System.out.println("1. the end");
			}

			public void onError(Throwable e) {
				System.out.println("error");
			}

			public void onNext(String s) {
				System.out.println(s);
			}
		};
		myObservable.subscribe(mySubscriber);

		// 2. almost same thing as above
		Observable.just("2. Hello, world!").subscribe(s -> System.out.println(s + "-Krzysztof"));

		// 3. map operator - transforming
		Observable.just("3. Hello, world!").map(s -> s + "-Krzysztof")
				.subscribe(s -> System.out.println(s));
				// http://reactivex.io/documentation/operators/map.html

		// 4. subscriber receive Integer
		Observable.just("4. Hello, world!").map(s -> s.hashCode())
				.subscribe(i -> System.out.println("4. " + Integer.toString(i)));

		// 5. subscriber shouldn't have much logic so...
		Observable.just("5. Hello, world!").map(s -> s.hashCode()).map(i -> Integer.toString(i))
				.subscribe(s -> System.out.println("5. " + s));

		// 6. some transformations
		Observable.just("6. Hello, world!").map(s -> s + " -Krzysztof").map(s -> s.hashCode())
				.map(i -> Integer.toString(i)).subscribe(s -> System.out.println("6. " + s));

		List<String> arrayList = new ArrayList<String>();
		arrayList.add("Krzysztof");
		arrayList.add("Karol");
		arrayList.add("Irek");

		// 7. from operator emits one element each time
		Observable.just(arrayList).subscribe(names -> {
			Observable.from(names).subscribe(name -> System.out.println("7. Name: " + name));
		});
		// http://reactivex.io/documentation/operators/from.html

		// 8. list observable transformed into observable which emits single
		// result with after change name, filtering and taking entry at the end
		Observable.just(arrayList).flatMap(names -> Observable.from(names))
				.flatMap(name -> Observable.just(name + " is awesome"))
				.filter(nameChange -> !"Karol is awesome".equals(nameChange)).take(1)
				.subscribe(result -> System.out.println("8. " + result + "- this is the result"));
				// http://reactivex.io/documentation/operators/flatmap.html

		// 9. doOnNext() allows us to add extra behavior each time an item is
		// emitted, in this case singing 'lalala'
		Observable.just(arrayList).flatMap(names -> Observable.from(names))
				.flatMap(name -> Observable.just(name + " is awesome"))
				.filter(nameChange -> !"Irek is awesome".equals(nameChange)).take(1)
				.doOnNext(nameChange -> System.out.println("9. lalalla"))
				.subscribe(result -> System.out.println("9. " + result + "- this is the result"));
				// http://reactivex.io/documentation/operators/filter.html
				// http://reactivex.io/RxJava/javadoc/rx/Observable.html#doOnNext(rx.functions.Action1)

		// 10. error example
		Observable.just(arrayList).flatMap(names -> Observable.from(names))
				.flatMap(name -> Observable.just(name + " is awesome"))
				.filter(nameChange -> getError(nameChange).equals("anything")).take(1)
				.doOnNext(nameChange -> System.out.println("10. lalalla"))
				.onErrorReturn(new Func1<Throwable, String>() {
					@Override
					public String call(Throwable t) {
						return "error";
					}
				})
				.subscribe(result -> System.out.println("10. " + result + " - this is the result"));

		// 11. Schedulers: easy threading
		// myObservableServices.retrieveImage(url)
		// .subscribeOn(Schedulers.io())
		// .observeOn(AndroidSchedulers.mainThread())
		// .subscribe(bitmap -> myImageView.setImageBitmap(bitmap));

		// subscribeOn(Scheduler scheduler): Asynchronously subscribes Observers
		// to this Observable on the specified Scheduler.

		// observeOn(Scheduler scheduler): Modifies an Observable to perform its
		// emissions and notifications on a specified Scheduler, asynchronously
		// with a bounded buffer.

		// check: http://reactivex.io/documentation/operators/subscribeon.html

	}

	private static String getError(String name) {
		throw new RuntimeException();
	}

	// OUTPUT:
	// 1. Hello, world!
	// 1. the end
	// 2. Hello, world!-Krzysztof
	// 3. Hello, world!-Krzysztof
	// 4. -1028118321
	// 5. -1538652498
	// 6. -1846029788
	// 7. Name: Krzysztof
	// 7. Name: Karol
	// 7. Name: Irek
	// 8. Krzysztof is awesome- this is the result
	// 9. lalalla
	// 9. Krzysztof is awesome- this is the result
	// 10. error - this is the result

}

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