一次Observable的empty和never方法的rx源码笔记

Observable.just(1,2,3,4,5)
    .flatMap((Func1<Integer, Observable<Object>>) integer -> {
        if (integer > 3) {
            return Observable.empty();
            //return Observable.never();
        } else {
            return Observable.just(integer);
        }
    })
    .subscribe(new Subscriber<Object>() {
        @Override
        public void onCompleted() {
            System.out.println("onCompleted");
        }
        @Override
        public void onError(Throwable e) {
            System.out.println("onError");
        }
        @Override
        public void onNext(Object o) {
            System.out.println("onNext");
            System.out.println(Integer.valueOf(o.toString()));
        }
    });

onNext
1
onNext
2
onNext
3

onNext
1
onNext
2
onNext
3
onCompleted

public class Observable<T> {
    public static <T> Observable<T> never() {
        return NeverObservableHolder.instance();
    }
    /***部分代码省略***/
    public static <T> Observable<T> empty() {
        return EmptyObservableHolder.instance();
    }
}

public enum EmptyObservableHolder implements OnSubscribe<Object> {
    INSTANCE;
    static final Observable<Object> EMPTY = Observable.unsafeCreate(INSTANCE);
    @SuppressWarnings("unchecked")
    public static <T> Observable<T> instance() {
        return (Observable<T>)EMPTY;
    }
    @Override
    public void call(Subscriber<? super Object> child) {
        child.onCompleted();
    }
}

public enum NeverObservableHolder implements OnSubscribe<Object> {
    INSTANCE;
    static final Observable<Object> NEVER = Observable.unsafeCreate(INSTANCE);
    @SuppressWarnings("unchecked")
    public static <T> Observable<T> instance() {
        return (Observable<T>)NEVER;
    }
    @Override
    public void call(Subscriber<? super Object> child) {
        // deliberately no op
    }
}