FlatMapExample.java

/*******************************************************************************
 * Copyright (c) 2015 Christos Froussios
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 *******************************************************************************/
package itrx.chapter2.transforming;

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.concurrent.TimeUnit;

import org.junit.Test;

import rx.Observable;
import rx.Subscriber;
import rx.observers.TestSubscriber;
import rx.schedulers.Schedulers;
import rx.schedulers.TestScheduler;

public class FlatMapExample {
	
	private static class PrintSubscriber extends Subscriber<Object>{
	    private final String name;
	    public PrintSubscriber(String name) {
	        this.name = name;
	    }
	    @Override
	    public void onCompleted() {
	        System.out.println(name + ": Completed");
	    }
	    @Override
	    public void onError(Throwable e) {
	        System.out.println(name + ": Error: " + e);
	    }
	    @Override
	    public void onNext(Object v) {
	        System.out.println(name + ": " + v);
	    }
	}

	public void exampleFlatMap() {
		Observable<Integer> values = Observable.just(2);

		values
		    .flatMap(i -> Observable.range(0,i))
		    .subscribe(new PrintSubscriber("flatMap"));
		
		// flatMap: 0
		// flatMap: 1
		// flatMap: Completed
	}
	
	public void exampleFlatMapMultipleValues() {
		Observable<Integer> values = Observable.range(1,3);

		values
		    .flatMap(i -> Observable.range(0,i))
		    .subscribe(new PrintSubscriber("flatMap"));
		
		// flatMap: 0
		// flatMap: 0
		// flatMap: 1
		// flatMap: 0
		// flatMap: 1
		// flatMap: 2
		// flatMap: Completed
	}
	
	public void exampleFlatMapNewType() {
		Observable<Integer> values = Observable.just(1);

		values
		    .flatMap(i -> 
		        Observable.just(
		            Character.valueOf((char)(i+64))
		    ))
		    .subscribe(new PrintSubscriber("flatMap"));
		
		// flatMap: A
		// flatMap: Completed
	}
	
	public void exampleFlatMapFilter() {
		Observable<Integer> values = Observable.range(0,30);

		values
		    .flatMap(i -> {
		        if (0 < i && i <= 26)
		            return Observable.just(Character.valueOf((char)(i+64)));
		        else
		            return Observable.empty();
		    })
		    .subscribe(new PrintSubscriber("flatMap"));
		
		// flatMap: A
		// flatMap: B
		// flatMap: C
		// ...
		// flatMap: X
		// flatMap: Y
		// flatMap: Z
		// flatMap: Completed
	}
	
	public void exampleFlatMapAsynchronous() {
		Observable.just(100, 150)
	    .flatMap(i ->
	        Observable.interval(i, TimeUnit.MILLISECONDS)
	            .map(v -> i)
	    )
	    .take(10)
	    .subscribe(new PrintSubscriber("flatMap"));
		
		// flatMap: 100
		// flatMap: 150
		// flatMap: 100
		// flatMap: 100
		// flatMap: 150
		// flatMap: 100
		// flatMap: 150
		// flatMap: 100
		// flatMap: 100
		// flatMap: 150
		// flatMap: Completed
	}
	
	
	//
	// Tests
	//
	
	@Test
	public void testFlatMap() {
		TestSubscriber<Integer> tester = new TestSubscriber<>();
		
		Observable<Integer> values = Observable.just(2);

		values
		    .flatMap(i -> Observable.range(0,i))
		    .subscribe(tester);
		
		tester.assertReceivedOnNext(Arrays.asList(0,1));
		tester.assertTerminalEvent();
		tester.assertNoErrors();
	}
	
	@Test
	public void testFlatMapMultipleValues() {
		TestSubscriber<Integer> tester = new TestSubscriber<>();
		
		Observable<Integer> values = Observable.range(1,3);

		values
		    .flatMap(i -> Observable.range(0,i))
		    .subscribe(tester);
		
		tester.assertReceivedOnNext(Arrays.asList(0,0,1,0,1,2));
		tester.assertTerminalEvent();
		tester.assertNoErrors();
		
	}
	
	@Test
	public void testFlatMapNewType() {
		TestSubscriber<Character> tester = new TestSubscriber<>();
		
		Observable<Integer> values = Observable.just(1);

		values
		    .flatMap(i -> 
		        Observable.just(
		            Character.valueOf((char)(i+64))
		    ))
		    .subscribe(tester);
		
		tester.assertReceivedOnNext(Arrays.asList('A'));
		tester.assertTerminalEvent();
		tester.assertNoErrors();
	}
	
	@Test
	public void testFlatMapFilter() {
		TestSubscriber<Character> tester = new TestSubscriber<>();
		
		Observable<Integer> values = Observable.range(0,30);

		values
		    .flatMap(i -> {
		        if (0 < i && i <= 26)
		            return Observable.just(Character.valueOf((char)(i+64)));
		        else
		            return Observable.empty();
		    })
		    .subscribe(tester);
		
		assertEquals(tester.getOnNextEvents().size(), 26);
		tester.assertTerminalEvent();
		tester.assertNoErrors();
	}
	
	@Test
	public void testFlatMapAsynchronous() {
		TestSubscriber<Object> tester = new TestSubscriber<>();
		TestScheduler scheduler = Schedulers.test();
		
		Observable.just(100, 150)
		    .flatMap(i ->
		        Observable.interval(i, TimeUnit.MILLISECONDS, scheduler)
		            .map(v -> i)
		    )
		    .take(10)
		    .distinctUntilChanged()
		    .subscribe(tester);
		
		scheduler.advanceTimeBy(2, TimeUnit.SECONDS);
		
		assertTrue(tester.getOnNextEvents().size() > 2); // 100 and 150 succeeded each other more than once
		tester.assertNoErrors();
	}
}