一、AsyncSubject
Observer會接收AsyncSubject的onComplete()之前的最后一個數(shù)據(jù)灰伟。

 AsyncSubject<String> asyncSubject = AsyncSubject.create();

        asyncSubject.onNext("asyncSubject1");
        asyncSubject.onNext("asyncSubject2");
        asyncSubject.onComplete();

        asyncSubject.subscribe(s -> System.out.println("asyncSubject: " + s));

結(jié)果：

asyncSubject: asyncSubject2

二拆又、BehaviorSubject
Observer會先接收到 BehaviorSubject被訂閱之前的最后一個數(shù)據(jù)， 再接收訂閱之后發(fā)射過 來的數(shù)據(jù)栏账。

 BehaviorSubject<String> behaviorSubject = BehaviorSubject.create();
        behaviorSubject.onNext("behaviorSubject1");
        behaviorSubject.onNext("behaviorSubject2");

        behaviorSubject.subscribe(s -> System.out.println("behaviorSubject: " + s));

        behaviorSubject.onNext("behaviorSubject3");
        behaviorSubject.onNext("behaviorSubject4");
        behaviorSubject.onComplete();

結(jié)果：

behaviorSubject: behaviorSubject2
behaviorSubject: behaviorSubject3
behaviorSubject: behaviorSubject4

三帖族、ReplaySubject
ReplaySubject 會發(fā)射所有來自原始 Observable 的數(shù)據(jù) 給觀察者，無論它 們 是何時(shí)訂閱的挡爵。

 ReplaySubject<String> replaySubject = ReplaySubject.create();
        replaySubject.onNext("replaySubject1");
        replaySubject.onNext("replaySubject2");

        replaySubject.subscribe(s -> System.out.println("replaySubject: " + s));

        replaySubject.onNext("replaySubject3");
        replaySubject.onNext("replaySubject4");
        replaySubject.onComplete();

結(jié)果：

replaySubject: replaySubject1
replaySubject: replaySubject2
replaySubject: replaySubject3
replaySubject: replaySubject4

四竖般、PublishSubject
Observer 只接收 PublishSubject 被訂閱之后發(fā)送的數(shù)據(jù)。

 PublishSubject<String> publishSubject = PublishSubject.create();
        publishSubject.onNext("publishSubject1");
        publishSubject.onNext("publishSubject2");

        publishSubject.subscribe(s -> System.out.println("publishSubject" + s));

        publishSubject.onNext("publishSubject3");
        publishSubject.onNext("publishSubject4");
        publishSubject.onComplete();

結(jié)果：

publishSubjectpublishSubject3
publishSubjectpublishSubject4

五茶鹃、總結(jié)
AsyncSubject：不論訂閱發(fā)生在什么時(shí)候涣雕，只發(fā)射最后一個數(shù)據(jù)。
BehaviorSubject：發(fā)送訂閱之前的一個數(shù)據(jù)和訂閱之后的全部數(shù)據(jù)闭翩。
ReplaySubject：不論訂閱發(fā)生在什么時(shí)候挣郭，都發(fā)射全部數(shù)據(jù)。
PublishSubject：發(fā)送訂閱之后全部數(shù)據(jù)疗韵。