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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 class Observers {

    private static final Observer EMPTY = new Observer() {

        @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. This is different, however, from an {@link EmptyObserver}, in
     * that it will throw an exception if its {@link Observer#onError onError} method is called (whereas
     * {@code EmptyObserver} will swallow the error in such a case).
     *
     * @return an inert {@code Observer}
     */
    @SuppressWarnings("unchecked")
    public static  Observer empty() {
        return (Observer) 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#onError onError} and
     * {@link Observer#onCompleted onCompleted} notifications.
     *
     * @param onNext
     *          a function that handles each item emitted by an {@code Observable}
     * @throws IllegalArgument Exception
     *          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  Observer create(final Action1 onNext) {
        if (onNext == null) {
            throw new IllegalArgumentException("onNext can not be null");
        }

        return new Observer() {

            @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 IllegalArgument Exception
     *          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  Observer create(final Action1 onNext, final Action1 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() {

            @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 IllegalArgument Exception
     *          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  Observer create(final Action1 onNext, final Action1 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() {

            @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);
            }

        };
    }

}
    
    
    
    

    




    
    
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