/** * Copyright (c) 2016-present, RxJava Contributors. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in * compliance with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software distributed under the License is * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See * the License for the specific language governing permissions and limitations under the License. */ package io.reactivex.observers; import io.reactivex.Observer; import io.reactivex.annotations.NonNull; import io.reactivex.disposables.Disposable; import io.reactivex.internal.disposables.DisposableHelper; import io.reactivex.internal.util.EndConsumerHelper; /** * Abstract base implementation of an {@link io.reactivex.Observer Observer} with support for cancelling a * subscription via {@link #cancel()} (synchronously) and calls {@link #onStart()} * when the subscription happens. * * <p>All pre-implemented final methods are thread-safe. * * <p>Use the protected {@link #cancel()} to dispose the sequence from within an * {@code onNext} implementation. * * <p>Like all other consumers, {@code DefaultObserver} can be subscribed only once. * Any subsequent attempt to subscribe it to a new source will yield an * {@link IllegalStateException} with message {@code "It is not allowed to subscribe with a(n) <class name> multiple times."}. * * <p>Implementation of {@link #onStart()}, {@link #onNext(Object)}, {@link #onError(Throwable)} * and {@link #onComplete()} are not allowed to throw any unchecked exceptions. * If for some reason this can't be avoided, use {@link io.reactivex.Observable#safeSubscribe(io.reactivex.Observer)} * instead of the standard {@code subscribe()} method. * * <p>Example<pre><code> * Observable.range(1, 5) * .subscribe(new DefaultObserver<Integer>() { * @Override public void onStart() { * System.out.println("Start!"); * } * @Override public void onNext(Integer t) { * if (t == 3) { * cancel(); * } * System.out.println(t); * } * @Override public void onError(Throwable t) { * t.printStackTrace(); * } * @Override public void onComplete() { * System.out.println("Done!"); * } * }); * </code></pre> * * @param <T> the value type */ public abstract class DefaultObserver<T> implements Observer<T> { private Disposable s; @Override public final void onSubscribe(@NonNull Disposable s) { if (EndConsumerHelper.validate(this.s, s, getClass())) { this.s = s; onStart(); } } /** * Cancels the upstream's disposable. */ protected final void cancel() { Disposable s = this.s; this.s = DisposableHelper.DISPOSED; s.dispose(); } /** * Called once the subscription has been set on this observer; override this * to perform initialization. */ protected void onStart() { } }