Observables

Operators

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Miscellaneous

RxJava Useful Resources

RxJava - Transforming Operators

Quiz

Following are the operators which are used to transform an item emitted from an Observable.

Sr.No.	Operator & Description
1	buffer Gathers items from Observable into bundles periodically and then emit the bundles rather than items.
2	flatMap Used in nested observables. Transforms items into Observables. Then flatten the items into single Observable.
3	groupBy Divide an Observable into set of Observables organized by key to emit different group of items.
4	map Apply a function to each emitted item to transform it.
5	scan Apply a function to each emitted item, sequentially and then emit the successive value.
6	window Gathers items from Observable into Observable windows periodically and then emit the windows rather than items.

Example - Transforming Letters to Upper case using map Operator

ObservableTester.java

package com.tutorialspoint;

import io.reactivex.rxjava3.core.Observable;

//Using map operator to tranform an item emitted
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);
   }
}

Output

Compile and Run the code to verify the following output −

ABCDEFG

Example - Flatten internal observables using flatmap Operator

ObservableTester.java

package com.tutorialspoint;

import java.util.concurrent.TimeUnit;

import io.reactivex.rxjava3.core.Observable;
import io.reactivex.rxjava3.schedulers.Schedulers;

//Using flatmap operator to flatten observables
public class ObservableTester  {
   public static void main(String[] args) throws InterruptedException { 
      Observable<String> userIds = Observable.just("user1", "user2", "user3");

      userIds.flatMap(userId -> getUserDetails(userId))
         .subscribe(userDetails -> System.out.println("Received: " + userDetails));

      // Keep the main thread alive to see the asynchronous results
      Thread.sleep(1000);
   }

   // Simulate an asynchronous network call to get user details
   public static Observable<String> getUserDetails(String userId) {
      return Observable.just("User Details of " + userId)
         .delay(100, TimeUnit.MILLISECONDS) 
         .subscribeOn(Schedulers.io());
   }
}

Output

Compile and Run the code to verify the following output −

Received: User Details of user3
Received: User Details of user1
Received: User Details of user2

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