2.x: Remove takeFirst(predicate) in Observable & Flowable (#4595)

Author: vanniktech

src/main/java/io/reactivex/Flowable.java

@@ -12341,32 +12341,6 @@ public final Flowable<T> take(long time, TimeUnit unit, Scheduler scheduler) {
         return takeUntil(timer(time, unit, scheduler));
     }
 
-    /**
-     * Returns a Flowable that emits only the very first item emitted by the source Publisher that satisfies
-     * a specified condition.
-     * <p>
-     * <img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/takeFirstN.png" alt="">
-     * <dl>
-     *  <dt><b>Backpressure:</b></dt>
-     *  <dd>The operator doesn't interfere with backpressure which is determined by the source {@code Publisher}'s backpressure
-     *  behavior.</dd>
-     *  <dt><b>Scheduler:</b></dt>
-     *  <dd>{@code takeFirst} does not operate by default on a particular {@link Scheduler}.</dd>
-     * </dl>
-     *
-     * @param predicate
-     *            the condition any item emitted by the source Publisher has to satisfy
-     * @return a Flowable that emits only the very first item emitted by the source Publisher that satisfies
-     *         the given condition, or that completes without emitting anything if the source Publisher
-     *         completes without emitting a single condition-satisfying item
-     * @see <a href="http://reactivex.io/documentation/operators/first.html">ReactiveX operators documentation: First</a>
-     */
-    @BackpressureSupport(BackpressureKind.SPECIAL) // may trigger UNBOUNDED_IN
-    @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> takeFirst(Predicate<? super T> predicate) {
-        return filter(predicate).take(1);
-    }
-
     /**
      * Returns a Flowable that emits at most the last {@code count} items emitted by the source Publisher. If the source emits fewer than
      * {@code count} items then all of its items are emitted.

src/main/java/io/reactivex/Observable.java

@@ -10333,28 +10333,6 @@ public final Observable<T> take(long time, TimeUnit unit, Scheduler scheduler) {
         return takeUntil(timer(time, unit, scheduler));
     }
 
-    /**
-     * Returns an Observable that emits only the very first item emitted by the source ObservableSource that satisfies
-     * a specified condition.
-     * <p>
-     * <img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/takeFirstN.png" alt="">
-     * <dl>
-     *  <dt><b>Scheduler:</b></dt>
-     *  <dd>{@code takeFirst} does not operate by default on a particular {@link Scheduler}.</dd>
-     * </dl>
-     *
-     * @param predicate
-     *            the condition any item emitted by the source ObservableSource has to satisfy
-     * @return an Observable that emits only the very first item emitted by the source ObservableSource that satisfies
-     *         the given condition, or that completes without emitting anything if the source ObservableSource
-     *         completes without emitting a single condition-satisfying item
-     * @see <a href="http://reactivex.io/documentation/operators/first.html">ReactiveX operators documentation: First</a>
-     */
-    @SchedulerSupport(SchedulerSupport.NONE)
-    public final Observable<T> takeFirst(Predicate<? super T> predicate) {
-        return filter(predicate).take(1);
-    }
-
     /**
      * Returns an Observable that emits at most the last {@code count} items emitted by the source ObservableSource. If the source emits fewer than
      * {@code count} items then all of its items are emitted.

src/test/java/io/reactivex/flowable/FlowableNullTests.java

@@ -2179,11 +2179,6 @@ public void takeTimedSchedulerNull() {
         just1.take(1, TimeUnit.SECONDS, null);
     }
 
-    @Test(expected = NullPointerException.class)
-    public void takeFirstNull() {
-        just1.takeFirst(null);
-    }
-
     @Test(expected = NullPointerException.class)
     public void takeLastTimedUnitNull() {
         just1.takeLast(1, null, Schedulers.single());
@@ -2957,4 +2952,4 @@ public Object apply(Object[] v) {
             }
         }, 128, just1).blockingLast();
     }
-}
+}

src/test/java/io/reactivex/flowable/FlowableTests.java

@@ -182,9 +182,10 @@ public Throwable call() {
         verify(wo, times(1)).onError(any(RuntimeException.class));
     }
 
+    @Test
     public void testTakeFirstWithPredicateOfSome() {
         Flowable<Integer> observable = Flowable.just(1, 3, 5, 4, 6, 3);
-        observable.takeFirst(IS_EVEN).subscribe(w);
+        observable.filter(IS_EVEN).take(1).subscribe(w);
         verify(w, times(1)).onNext(anyInt());
         verify(w).onNext(4);
         verify(w, times(1)).onComplete();
@@ -194,7 +195,7 @@ public void testTakeFirstWithPredicateOfSome() {
     @Test
     public void testTakeFirstWithPredicateOfNoneMatchingThePredicate() {
         Flowable<Integer> observable = Flowable.just(1, 3, 5, 7, 9, 7, 5, 3, 1);
-        observable.takeFirst(IS_EVEN).subscribe(w);
+        observable.filter(IS_EVEN).take(1).subscribe(w);
         verify(w, never()).onNext(anyInt());
         verify(w, times(1)).onComplete();
         verify(w, never()).onError(any(Throwable.class));

src/test/java/io/reactivex/observable/ObservableNullTests.java

@@ -2250,11 +2250,6 @@ public void takeTimedSchedulerNull() {
         just1.take(1, TimeUnit.SECONDS, null);
     }
 
-    @Test(expected = NullPointerException.class)
-    public void takeFirstNull() {
-        just1.takeFirst(null);
-    }
-
     @Test(expected = NullPointerException.class)
     public void takeLastTimedUnitNull() {
         just1.takeLast(1, null, Schedulers.single());

src/test/java/io/reactivex/observable/ObservableTest.java

@@ -186,7 +186,7 @@ public Throwable call() {
     @Test
     public void testTakeFirstWithPredicateOfSome() {
         Observable<Integer> o = Observable.just(1, 3, 5, 4, 6, 3);
-        o.takeFirst(IS_EVEN).subscribe(w);
+        o.filter(IS_EVEN).take(1).subscribe(w);
         verify(w, times(1)).onNext(anyInt());
         verify(w).onNext(4);
         verify(w, times(1)).onComplete();
@@ -196,7 +196,7 @@ public void testTakeFirstWithPredicateOfSome() {
     @Test
     public void testTakeFirstWithPredicateOfNoneMatchingThePredicate() {
         Observable<Integer> o = Observable.just(1, 3, 5, 7, 9, 7, 5, 3, 1);
-        o.takeFirst(IS_EVEN).subscribe(w);
+        o.filter(IS_EVEN).take(1).subscribe(w);
         verify(w, never()).onNext(anyInt());
         verify(w, times(1)).onComplete();
         verify(w, never()).onError(any(Throwable.class));