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

Let's take a look at the following code:

fun main(args: Array<String>) { 
 
    val observer: Observer<String> = object : Observer<String> { 
        override fun onComplete() { 
            println("Completed") 
        } 
 
        override fun onNext(item: String) { 
            println("Received-> $item") 
        } 
 
        override fun onError(e: Throwable) { 
            println("Error Occured => ${e.message}") 
        } 
 
        override fun onSubscribe(d: Disposable) { 
            println("Subscription") 
        } 
    }//Create Observer 
 
    val list = listOf("Str 1","Str 2","Str 3","Str 4") 
    val observableFromIterable: Observable<String> = Observable.fromIterable(list)//1 
    observableFromIterable.subscribe(observer) 
 
 
    val callable = object : Callable<String> { 
        override fun call(): String { 
            return "I'm From Callable" 
        } 
 
    } 
    val observableFromCallable:Observable<String> = Observable.fromCallable(callable)//2 
    observableFromCallable.subscribe(observer) 
 
    val future:Future<String> = object : Future<String> { 
        val retStr = "I'm from Future" 
 
        override fun get() = retStr 
 
        override fun get(timeout: Long, unit: TimeUnit?)  = retStr 
 
        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) 
} 

At comment 1, we used the Observable.fromIterable method to create Observable from an Iterable instance (here, list). At comment 2. We called the Observable.fromCallable method to create Observable from a Callable instance, we did the same at comment 3, where we called the Observable.fromFuture method to derive Observable from a Future instance.

Here is the output: