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/**

* Copyright 2014 Netflix, Inc.

*

* 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 rx.observers;

import rx.Observer;

import rx.exceptions.OnErrorNotImplementedException;

import rx.functions.Action0;

import rx.functions.Action1;

/**

* Helper methods and utilities for creating and working with {@link Observer} objects.

*/

public final class Observers {

private Observers() {

throw new IllegalStateException("No instances!");

}

private static final Observer<Object> EMPTY = new Observer<Object>() {

@Override

public final void onCompleted() {

// do nothing

}

@Override

public final void onError(Throwable e) {

throw new OnErrorNotImplementedException(e);

}

@Override

public final void onNext(Object args) {

// do nothing

}

};

/**

* Returns an inert {@link Observer} that does nothing in response to the emissions or notifications from

* any {@code Observable} it subscribes to but will throw an exception if its

* {@link Observer#onError onError} method is called.

*

* @return an inert {@code Observer}

*/

@SuppressWarnings("unchecked")

public static <T> Observer<T> empty() {

return (Observer<T>) EMPTY;

}

/**

* Creates an {@link Observer} that receives the emissions of any {@code Observable} it subscribes to via

* {@link Observer#onNext onNext} but ignores {@link Observer#onCompleted onCompleted} notifications;

* it will throw an {@link OnErrorNotImplementedException} if {@link Observer#onError onError} is invoked.

*

* @param onNext

* a function that handles each item emitted by an {@code Observable}

* @throws IllegalArgumentException

* if {@code onNext} is {@code null}

* @return an {@code Observer} that calls {@code onNext} for each emitted item from the {@code Observable}

* the {@code Observer} subscribes to

*/

public static final <T> Observer<T> create(final Action1<? super T> onNext) {

if (onNext == null) {

throw new IllegalArgumentException("onNext can not be null");

}

return new Observer<T>() {

@Override

public final void onCompleted() {

// do nothing

}

@Override

public final void onError(Throwable e) {

throw new OnErrorNotImplementedException(e);

}

@Override

public final void onNext(T args) {

onNext.call(args);

}

};

}

/**

* Creates an {@link Observer} that receives the emissions of any {@code Observable} it subscribes to via

* {@link Observer#onNext onNext} and handles any {@link Observer#onError onError} notification but ignores

* an {@link Observer#onCompleted onCompleted} notification.

*

* @param onNext

* a function that handles each item emitted by an {@code Observable}

* @param onError

* a function that handles an error notification if one is sent by an {@code Observable}

* @throws IllegalArgumentException

* if either {@code onNext} or {@code onError} are {@code null}

* @return an {@code Observer} that calls {@code onNext} for each emitted item from the {@code Observable}

* the {@code Observer} subscribes to, and calls {@code onError} if the {@code Observable} notifies

* of an error

*/

public static final <T> Observer<T> create(final Action1<? super T> onNext, final Action1<Throwable> onError) {

if (onNext == null) {

throw new IllegalArgumentException("onNext can not be null");

}

if (onError == null) {

throw new IllegalArgumentException("onError can not be null");

}

return new Observer<T>() {

@Override

public final void onCompleted() {

// do nothing

}

@Override

public final void onError(Throwable e) {

onError.call(e);

}

@Override

public final void onNext(T args) {

onNext.call(args);

}

};

}

/**

* Creates an {@link Observer} that receives the emissions of any {@code Observable} it subscribes to via

* {@link Observer#onNext onNext} and handles any {@link Observer#onError onError} or

* {@link Observer#onCompleted onCompleted} notifications.

*

* @param onNext

* a function that handles each item emitted by an {@code Observable}

* @param onError

* a function that handles an error notification if one is sent by an {@code Observable}

* @param onComplete

* a function that handles a sequence complete notification if one is sent by an {@code Observable}

* @throws IllegalArgumentException

* if either {@code onNext}, {@code onError}, or {@code onComplete} are {@code null}

* @return an {@code Observer} that calls {@code onNext} for each emitted item from the {@code Observable}

* the {@code Observer} subscribes to, calls {@code onError} if the {@code Observable} notifies

* of an error, and calls {@code onComplete} if the {@code Observable} notifies that the observable

* sequence is complete

*/

public static final <T> Observer<T> create(final Action1<? super T> onNext, final Action1<Throwable> onError, final Action0 onComplete) {

if (onNext == null) {

throw new IllegalArgumentException("onNext can not be null");

}

if (onError == null) {

throw new IllegalArgumentException("onError can not be null");

}

if (onComplete == null) {

throw new IllegalArgumentException("onComplete can not be null");

}

return new Observer<T>() {

@Override

public final void onCompleted() {

onComplete.call();

}

@Override

public final void onError(Throwable e) {

onError.call(e);

}

@Override

public final void onNext(T args) {

onNext.call(args);

}

};

}

}