Blocking Observable Operators

This section explains the BlockingObservable subclass. A Blocking Observable extends the ordinary Observable class by providing a set of operators on the items emitted by the Observable that block.

To transform an Observable into a BlockingObservable, use the Observable.toBlocking( ) method or the BlockingObservable.from( ) method.

• forEach( ) — invoke a function on each item emitted by the Observable; block until the Observable completes
• first( ) — block until the Observable emits an item, then return the first item emitted by the Observable
• firstOrDefault( ) — block until the Observable emits an item or completes, then return the first item emitted by the Observable or a default item if the Observable did not emit an item
• last( ) — block until the Observable completes, then return the last item emitted by the Observable
• lastOrDefault( ) — block until the Observable completes, then return the last item emitted by the Observable or a default item if there is no last item
• mostRecent( ) — returns an iterable that always returns the item most recently emitted by the Observable
• next( ) — returns an iterable that blocks until the Observable emits another item, then returns that item
• latest( ) — returns an iterable that blocks until or unless the Observable emits an item that has not been returned by the iterable, then returns that item
• single( ) — if the Observable completes after emitting a single item, return that item, otherwise throw an exception
• singleOrDefault( ) — if the Observable completes after emitting a single item, return that item, otherwise return a default item
• toFuture( ) — convert the Observable into a Future
• toIterable( ) — convert the sequence emitted by the Observable into an Iterable
• getIterator( ) — convert the sequence emitted by the Observable into an Iterator

This documentation accompanies its explanations with a modified form of "marble diagrams." Here is how these marble diagrams represent Blocking Observables:

see also:

• javadoc: <a href="http://reactivex.io/RxJava/javadoc/rx/observables/BlockingObservable.html">BlockingObservable</a>
• javadoc: <a href="http://reactivex.io/RxJava/javadoc/rx/Observable.html#toBlocking()">toBlocking()</a>
• javadoc: <a href="http://reactivex.io/RxJava/javadoc/rx/observables/BlockingObservable.html#from(rx.Observable)">BlockingObservable.from()</a>

Appendix: similar blocking and non-blocking operators

<table> <thead> <tr><th rowspan="2">operator</th><th colspan="3">result when it acts on</th><th rowspan="2">equivalent in Rx.NET</th></tr> <tr><th>Observable that emits multiple items</th><th>Observable that emits one item</th><th>Observable that emits no items</th></tr> </thead> <tbody> <tr><td><code>Observable.first</code></td><td>the first item</td><td>the single item</td><td><i>NoSuchElement</i></td><td><code>firstAsync</code></td></tr> <tr><td><code>BlockingObservable.first</code></td><td>the first item</td><td>the single item</td><td><i>NoSuchElement</i></td><td><code>first</code></td></tr> <tr><td><code>Observable.firstOrDefault</code></td><td>the first item</td><td>the single item</td><td>the default item</td><td><code>firstOrDefaultAsync</code></td></tr> <tr><td><code>BlockingObservable.firstOrDefault</code></td><td>the first item</td><td>the single item</td><td>the default item</td><td><code>firstOrDefault</code></td></tr> <tr><td><code>Observable.last</code></td><td>the last item</td><td>the single item</td><td><i>NoSuchElement</i></td><td><code>lastAsync</code></td></tr> <tr><td><code>BlockingObservable.last</code></td><td>the last item</td><td>the single item</td><td><i>NoSuchElement</i></td><td><code>last</code></td></tr> <tr><td><code>Observable.lastOrDefault</code></td><td>the last item</td><td>the single item</td><td>the default item</td><td><code>lastOrDefaultAsync</code></td></tr> <tr><td><code>BlockingObservable.lastOrDefault</code></td><td>the last item</td><td>the single item</td><td>the default item</td><td><code>lastOrDefault</code></td></tr> <tr><td><code>Observable.single</code></td><td><i>Illegal Argument</i></td><td>the single item</td><td><i>NoSuchElement</i></td><td><code>singleAsync</code></td></tr> <tr><td><code>BlockingObservable.single</code></td><td><i>Illegal Argument</i></td><td>the single item</td><td><i>NoSuchElement</i></td><td><code>single</code></td></tr> <tr><td><code>Observable.singleOrDefault</code></td><td><i>Illegal Argument</i></td><td>the single item</td><td>the default item</td><td><code>singleOrDefaultAsync</code></td></tr> <tr><td><code>BlockingObservable.singleOrDefault</code></td><td><i>Illegal Argument</i></td><td>the single item</td><td>the default item</td><td><code>singleOrDefault</code></td></tr> </tbody> </table>