The Observable.from methods are comparatively simpler than the Observable.create method. You can create Observable instances from nearly every Kotlin structure with the help of from methods.

So, let's take a look at this code:

    fun main(args: Array<String>) { 
 
      val observer: Observer<String> = object : Observer<String> { 
        override fun onComplete() { 
          println("All Completed") 
        } 
 
        override fun onNext(item: String) { 
          println("Next $item") 
        } 
 
        override fun onError(e: Throwable) { 
          println("Error Occured ${e.message}") 
        } 
 
        override fun onSubscribe(d: Disposable) { 
          println("New Subscription ") 
        } 
      }//Create Observer 
 
      val list = listOf("String 1","String 2","String 3","String 4") 
      val observableFromIterable: Observable<String> =
      Observable.fromIterable(list)//1 
      observableFromIterable.subscribe(observer) 
 
 
      val callable = object : Callable<String> { 
        override fun call(): String { 
          return "From Callable" 
        } 
      } 
      val observableFromCallable:Observable<String> =
      Observable.fromCallable(callable)//2 
      observableFromCallable.subscribe(observer) 
 
      val future:Future<String> = object :Future<String> { 
        override fun get(): String = "Hello From Future" 
 
        override fun get(timeout: Long, unit: TimeUnit?): String  =
        "Hello From Future" 
 
        override fun isDone(): Boolean = true 
 
        override fun isCancelled(): Boolean = false 
 
        override fun cancel(mayInterruptIfRunning: Boolean):
        Boolean = false 
 
      } 
      val observableFromFuture:Observable<String> = 
      Observable.fromFuture(future)//3 
      observableFromFuture.subscribe(observer) 
    } 

On comment 1, I used the Observable.fromIterable method to create Observable from an Iterable instance (here, List). On comment 2, I called the Observable.fromCallable method to create Observable from a Callable instance, and same for comment 3, where I called the Observable.fromFuture method to derive Observable from a Future instance.

Here is the output: