    001    /*
    002     * Copyright (C) 2011 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.util.concurrent;
    018
    019    import com.google.common.annotations.Beta;
    020
    021    import java.util.concurrent.Future;
    022
    023    /**
    024     * Transforms a value, possibly asynchronously. For an example usage and more
    025     * information, see {@link Futures#transform(ListenableFuture, AsyncFunction)}.
    026     *
    027     * @author Chris Povirk
    028     * @since 11.0
    029     */
    030    @Beta
    031    public interface AsyncFunction<I, O> {
    032      /**
    033       * Returns an output {@code Future} to use in place of the given {@code
    034       * input}. The output {@code Future} need not be {@linkplain Future#isDone
    035       * done}, making {@code AsyncFunction} suitable for asynchronous derivations.
    036       *
    037       * <p>Throwing an exception from this method is equivalent to returning a
    038       * failing {@code Future}.
    039       */
    040      ListenableFuture<O> apply(I input) throws Exception;
    041    }