RxJava example that shows how dependent data is dynamically updated when other data changes

ReactiveSum.java

package com.reactive.summing;
import com.reactive.helpers.RxHelpers;
import rx.Observable;
import rx.subjects.BehaviorSubject;

public class ReactiveSum {
	private BehaviorSubject<Double> a = BehaviorSubject.create(0.0);
	private BehaviorSubject<Double> b = BehaviorSubject.create(0.0);
	private BehaviorSubject<Double> c = BehaviorSubject.create(0.0);

	public ReactiveSum() {
		Observable.combineLatest(a, b, (x, y) -> x + y).subscribe(c);
	}

	public double getA() {
		return a.getValue();
	}

	public void setA(double a) {
		this.a.onNext(a);
	}

	public Observable<Double> obsA() {
		return a.asObservable();
	}

	public double getB() {
		return b.getValue();
	}

	public void setB(double b) {
		this.b.onNext(b);
	}

	public Observable<Double> obsB() {
		return b.asObservable();
	}

	public double getC() {
		return c.getValue();
	}

	public Observable<Double> obsC() {
		return c.asObservable();
	}
	public static void main(String[] args) {
		ReactiveSum sum = new ReactiveSum();
		RxHelpers.subscribePrint(sum.obsC(), "Sum");
		sum.setA(5);
		sum.setB(4);
		sum.setA(9);
		sum.setB(0);
		/* prints
			main|Sum : 0.0
			main|Sum : 5.0
			main|Sum : 9.0
			main|Sum : 13.0
			main|Sum : 9.0
		*/
	}
}

RxHelpers.java

package com.reactive.helpers;

import java.util.Arrays;
import java.util.stream.Collectors;

import rx.Observable;
import rx.Subscription;

public final class RxHelpers {

	public static <T> Subscription subscribePrint(Observable<T> observable, String name) {
		return observable.subscribe(
				(v) -> System.out.println(Thread.currentThread().getName()
						+ "|" + name + " : " + v), (e) -> {
					System.err.println("Error from " + name + ":");
					System.err.println(e);
					System.err.println(Arrays
							.stream(e.getStackTrace())
							.limit(5L)
							.map(stackEl -> "  " + stackEl)
							.collect(Collectors.joining("\n"))
							);
				}, () -> System.out.println(name + " ended!"));
	}
}