Simple example of getting an item on an interval, filtering, taking, and printing...

ShowItem.java

package rxExample;

import io.reactivex.Observable;
import io.reactivex.schedulers.TestScheduler;

import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.TimeUnit;

import static java.util.Arrays.asList;

/**
 * Created by mmynsted on 2/8/17.
 */
public class ShowItem {
    public void printGoodItem() {
        TestScheduler scheduler = new TestScheduler();  //control Observable's timing

        //Some test data
        List<List<Integer>> testSource = asList(
                Collections.emptyList(),
                asList(1),
                asList(1, 2),
                asList( 1, 2, 3));
        Iterator<List<Integer>> iter = testSource.iterator();

        Observable.interval(1, TimeUnit.SECONDS, scheduler) //1 sec interval with TestScheduler
                .map(y -> getTestItem(iter))                //map the int from iterval to a test item
                .filter(y -> y.size() > 1)                  //filter out any items where size < 1
                .take(1)                                    //take only the first item
                .subscribe(System.out::println);            //print the item
        scheduler.advanceTimeBy(5, TimeUnit.SECONDS);
    }

    private List<Integer> getTestItem(Iterator<List<Integer>> iter) {
        List<Integer> result = Collections.emptyList();
        if (iter != null) {
            if (iter.hasNext()) {
                result = iter.next();
            }
        }
        return result;
    }
}