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/*
* Copyright (c) OSGi Alliance (2014). All Rights Reserved.
*
* 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 org.osgi.util.promise;
import org.osgi.annotation.versioning.ConsumerType;
/**
* Success callback for a Promise.
*
* <p>
* A Success callback is registered with a {@link Promise} using the
* {@link Promise#then(Success)} method and is called if the Promise is resolved
* successfully.
*
* <p>
* This is a functional interface and can be used as the assignment target for a
* lambda expression or method reference.
*
* @param <T> The value type of the resolved Promise passed as input to this
* callback.
* @param <R> The value type of the returned Promise from this callback.
*
* @ThreadSafe
* @author $Id$
*/
@ConsumerType
public interface Success<T, R> {
/**
* Success callback for a Promise.
*
* <p>
* This method is called if the Promise with which it is registered resolves
* successfully.
*
* <p>
* In the remainder of this description we will refer to the Promise
* returned by this method as the returned Promise and the Promise returned
* by {@link Promise#then(Success)} when this Success callback was
* registered as the chained Promise.
*
* <p>
* If the returned Promise is {@code null} then the chained Promise must
* resolve immediately with a successful value of {@code null}. If the
* returned Promise is not {@code null} then the chained Promise must be
* resolved when the returned Promise is resolved.
*
* @param resolved The successfully resolved {@link Promise}.
* @return The Promise to use to resolve the chained Promise, or
* {@code null} if the chained Promise is to be resolved immediately
* with the value {@code null}.
* @throws Exception The chained Promise must be failed with the thrown
* exception.
*/
Promise<R> call(Promise<T> resolved) throws Exception;
}
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