Observable provides support to emit the data from any iterable sources, for example, lists, maps, sets, and so on. It will call onNext() on each item of an iterable type, and once the iterator is over, it will call onComplete() automatically. Iterable in Java is commonly used in collection frameworks, so Observable with iterable can be used while fetching data from collection classes.

Let's see how to use it as follows:

public class RxJavaIterableDemo {
  public static void main(String[] args) {
    List<EmployeeRating> employeeList = new ArrayList<EmployeeRating>();
    EmployeeRating employeeRating1 = new EmployeeRating();
    employeeRating1.setName("Lilly");
    employeeRating1.setRating(6);
    employeeList.add(employeeRating1);

    employeeRating1 = new EmployeeRating();
    employeeRating1.setName("Peter");
    employeeRating1.setRating(5);
    employeeList.add(employeeRating1);

    employeeRating1 = new EmployeeRating();
    employeeRating1.setName("Bhakti");
    employeeRating1.setRating(9);
    employeeList.add(employeeRating1);

    employeeRating1 = new EmployeeRating();
    employeeRating1.setName("Harmi");
    employeeRating1.setRating(9);
    employeeList.add(employeeRating1);

    Observable<EmployeeRating> employeeRatingSource = 
                                Observable.fromIterable(employeeList);

    employeeRatingSource.filter(employeeRating -> 
                employeeRating.getRating() >=7).subscribe(empRating -> 
                System.out.println("Star Employee: " + empRating.getName() 
                + " Rating : "+empRating.getRating()));
  }
}

We are populating the list of EmployeeRating and creating Observable with thefromIterable() method by passing this list. The class EmployeeRating is a simple POJO containing the name and rating attributes as follows:

class EmployeeRating{
  private String name;
  private int rating;
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public int getRating() {
    return rating;
  }
  public void setRating(int rating) {
    this.rating = rating;
  }
}

RxJava conforms to Reactive Streams specification by providing an implementation of interfaces. Let's recall that the onNext(), onError(), onSubscribe(), and onComplete() methods are part of the Observer interface. RxJava provides an implementation of these interfaces to handle respective events.