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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.subscriptions;

import java.util.concurrent.Future;

import rx.Subscription;

import rx.functions.Action0;

/**

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

*/

public final class Subscriptions {

private Subscriptions() {

throw new IllegalStateException("No instances!");

}

/**

* Returns a {@link Subscription} to which {@code unsubscribe} does nothing except to change

* {@code isUnsubscribed} to {@code true}. It's stateful and {@code isUnsubscribed} indicates if

* {@code unsubscribe} is called, which is different from {@link #unsubscribed()}.

*

* <pre><code>

* Subscription empty = Subscriptions.empty();

* System.out.println(empty.isUnsubscribed()); // false

* empty.unsubscribe();

* System.out.println(empty.isUnsubscribed()); // true

* </code></pre>

*

* @return a {@link Subscription} to which {@code unsubscribe} does nothing except to change

* {@code isUnsubscribed} to {@code true}

*/

public static Subscription empty() {

return BooleanSubscription.create();

}

/**

* Returns a {@link Subscription} to which {@code unsubscribe} does nothing, as it is already unsubscribed.

* Its {@code isUnsubscribed} always returns {@code true}, which is different from {@link #empty()}.

*

* <pre><code>

* Subscription unsubscribed = Subscriptions.unsubscribed();

* System.out.println(unsubscribed.isUnsubscribed()); // true

* </code></pre>

*

* @return a {@link Subscription} to which {@code unsubscribe} does nothing, as it is already unsubscribed

* @since 1.1.0

*/

public static Subscription unsubscribed() {

return UNSUBSCRIBED;

}

/**

* Creates and returns a {@link Subscription} that invokes the given {@link Action0} when unsubscribed.

*

* @param unsubscribe

* Action to invoke on unsubscribe.

* @return {@link Subscription}

*/

public static Subscription create(final Action0 unsubscribe) {

return BooleanSubscription.create(unsubscribe);

}

/**

* Converts a {@link Future} into a {@link Subscription} and cancels it when unsubscribed.

*

* @param f

* the {@link Future} to convert

* @return a {@link Subscription} that wraps {@code f}

*/

public static Subscription from(final Future<?> f) {

return new FutureSubscription(f);

}

/** Naming classes helps with debugging. */

private static final class FutureSubscription implements Subscription {

final Future<?> f;

public FutureSubscription(Future<?> f) {

this.f = f;

}

@Override

public void unsubscribe() {

f.cancel(true);

}

@Override

public boolean isUnsubscribed() {

return f.isCancelled();

}

}

/**

* Converts a set of {@link Subscription}s into a {@link CompositeSubscription} that groups the multiple

* Subscriptions together and unsubscribes from all of them together.

*

* @param subscriptions

* the Subscriptions to group together

* @return a {@link CompositeSubscription} representing the {@code subscriptions} set

*/

public static CompositeSubscription from(Subscription... subscriptions) {

return new CompositeSubscription(subscriptions);

}

/**

* A {@link Subscription} that does nothing when its unsubscribe method is called.

*/

private static final Unsubscribed UNSUBSCRIBED = new Unsubscribed();

/** Naming classes helps with debugging. */

static final class Unsubscribed implements Subscription {

@Override

public void unsubscribe() {

}

@Override

public boolean isUnsubscribed() {

return true;

}

}

}