RxJava - Creating Operators

Following are the operators which are used to create an Observable.

Sr.No. Operator & Description
1

Create

Creates an Observable from scratch and allows observer method to call programmatically.
2

Defer

Do not create an Observable until an observer subscribes. Creates a fresh observable for each observer.
3

Empty/Never/Throw

Creates an Observable with limited behavior.
4

From

Converts an object/data structure into an Observable.
5

Interval

Creates an Observable emitting integers in sequence with a gap of specified time interval.
6

Just

Converts an object/data structure into an Observable to emit the same or same type of objects.
7

Range

Creates an Observable emitting integers in sequence of given range.
8

Repeat

Creates an Observable emitting integers in sequence repeatedly.
9

Start

Creates an Observable to emit the return value of a function.
10

Timer

Creates an Observable to emit a single item after given delay.

Creating Operator Example

Create the following Java program using any editor of your choice in, say, C:\> RxJava.

ObservableTester.java

import io.reactivex.Observable;
//Using fromArray operator to create an Observable
public class ObservableTester  {
   public static void main(String[] args) { 
      String[] letters = {"a", "b", "c", "d", "e", "f", "g"};
      final StringBuilder result = new StringBuilder();
      Observable<String> observable = Observable.fromArray(letters);
      observable
         .map(String::toUpperCase)
         .subscribe( letter -> result.append(letter));
      System.out.println(result);
   }
}

Verify the Result

Compile the class using javac compiler as follows −

C:\RxJava>javac ObservableTester.java

Now run the ObservableTester as follows −

C:\RxJava>java ObservableTester

It should produce the following output −

ABCDEFG
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