hot-cold-observable's Introduction

Hot-Cold-Observable

Cold Observable

Observable only emit item when has subscribe
It will emit again when has new subscribe

Example:

var coldObservable = Observable.create<Int> {
    for (i in 0..2) {
        println("Source Emit $i")
        it.onNext(i)
    }
}

coldObservable.subscribe({
    println("onNext, subscriber1: $it")
}, {})
coldObservable.subscribe({
    println( "onNext, subscriber2: $it")
}, {})

Result:

Source Emit 0
onNext, subscriber1: 0
Source Emit 1
onNext, subscriber1: 1
Source Emit 2
onNext, subscriber1: 2
Source Emit 0
onNext, subscriber2: 0
Source Emit 1
onNext, subscriber2: 1
Source Emit 2
onNext, subscriber2: 2

Hot Observable

Observable emit item when created
Observable doesn't again emit when has a new subscribe

Example

var coldObservable = Observable.interval(1, TimeUnit.SECONDS)
    .doOnNext {
        println("Emitted $it")
    }
var connectableObservable: ConnectableObservable<Long> = coldObservable.publish()

connectableObservable.connect()

Thread.sleep(2000)

connectableObservable.subscribe({
    println("onNext, subscriber1: $it")
}, {})

Thread.sleep(2000)
connectableObservable.subscribe({
    println( "onNext, subscriber2: $it")
}, {}))

Result

Emitted 0
Emitted 1
Emitted 2
    onNext, subscriber1: 2
Emitted 3
    onNext, subscriber1: 3
Emitted 4
    onNext, subscriber1: 4
    onNext, subscriber2: 4