RxJava - Single Observable

The Single class represents the single value response. Single observable can only emit either a single successful value or an error. It does not emit onComplete event.

Class Declaration

Following is the declaration for io.reactivex.rxjava3.core.Single<T> class −

public abstract class Single<T>
   extends Object
      implements SingleSource<T>

Protocol

Following is the sequential protocol that Single Observable operates −

onSubscribe (onSuccess | onError)?

Example - Creating a Single Observable Class to get Data

ObservableTester.java

package com.tutorialspoint;

import io.reactivex.rxjava3.core.Single;

public class ObservableTester  {
   public static void main(String[] args)  throws InterruptedException {
      Single.just("Hello world").subscribe(System.out::println);
   }
}

Output

Compile and Run the code to verify the following output −

Hello World

Example - Usage of Single Observable Class to get Data after a delay of 2 seconds

ObservableTester.java

package com.tutorialspoint;

import java.util.concurrent.TimeUnit;

import io.reactivex.rxjava3.core.Single;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.observers.DisposableSingleObserver;
import io.reactivex.rxjava3.schedulers.Schedulers;

public class ObservableTester  {
   public static void main(String[] args)  throws InterruptedException {
      //Create the observable
      Single<String> testSingle = Single.just("Hello World");

      //Create an observer
      Disposable disposable = testSingle
         .delay(2, TimeUnit.SECONDS, Schedulers.io())
         .subscribeWith(
         new DisposableSingleObserver<String>() {

         @Override
         public void onError(Throwable e) { 
            e.printStackTrace();
         }

         @Override
         public void onSuccess(String value) {
            System.out.println(value);
         }
      }); 
      Thread.sleep(3000);
      //start observing
      disposable.dispose();
   }
}

Output

Compile and Run the code to verify the following output −

Hello World