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Java example source code file (CollectionFuture.java)

This example Java source code file (CollectionFuture.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

aggregatefuture, annotation, collectionfuturerunningstate, gwtcompatible, immutablecollection, list, listenablefuture, listfuturerunningstate, nullable, optional, override, util

The CollectionFuture.java Java example source code

/*
 * Copyright (C) 2006 The Guava Authors
 *
 * 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 com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.Lists.newArrayListWithCapacity;
import static java.util.Collections.unmodifiableList;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Optional;
import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;

import java.util.List;

import javax.annotation.Nullable;

/**
 * Aggregate future that collects (stores) results of each future.
 */
@GwtCompatible(emulated = true)
abstract class CollectionFuture<V, C> extends AggregateFuture {

  abstract class CollectionFutureRunningState extends RunningState {
    private List<Optional values;

    CollectionFutureRunningState(
        ImmutableCollection<? extends ListenableFuture futures,
        boolean allMustSucceed) {
      super(futures, allMustSucceed, true);

      this.values =
          futures.isEmpty()
              ? ImmutableList.<Optionalof()
              : Lists.<OptionalnewArrayListWithCapacity(futures.size());

      // Populate the results list with null initially.
      for (int i = 0; i < futures.size(); ++i) {
        values.add(null);
      }
    }

    @Override
    final void collectOneValue(boolean allMustSucceed, int index, @Nullable V returnValue) {
      List<Optional localValues = values;

      if (localValues != null) {
        localValues.set(index, Optional.fromNullable(returnValue));
      } else {
        // Some other future failed or has been cancelled, causing this one to also be cancelled or
        // have an exception set. This should only happen if allMustSucceed is true or if the output
        // itself has been cancelled.
        checkState(
            allMustSucceed || isCancelled(), "Future was done before all dependencies completed");
      }
    }

    @Override
    final void handleAllCompleted() {
      List<Optional localValues = values;
      if (localValues != null) {
        set(combine(localValues));
      } else {
        checkState(isDone());
      }
    }

    @Override
    void releaseResourcesAfterFailure() {
      super.releaseResourcesAfterFailure();
      this.values = null;
    }

    abstract C combine(List<Optional values);
  }

  /** Used for {@link Futures#allAsList} and {@link Futures#successfulAsList}. */
  static final class ListFuture<V> extends CollectionFuture> {
    ListFuture(
        ImmutableCollection<? extends ListenableFuture futures,
        boolean allMustSucceed) {
      init(new ListFutureRunningState(futures, allMustSucceed));
    }

    private final class ListFutureRunningState extends CollectionFutureRunningState {
      ListFutureRunningState(
          ImmutableCollection<? extends ListenableFuture futures,
          boolean allMustSucceed) {
        super(futures, allMustSucceed);
      }

      @Override
      public List<V> combine(List> values) {
        List<V> result = newArrayListWithCapacity(values.size());
        for (Optional<V> element : values) {
          result.add(element != null ? element.orNull() : null);
        }
        return unmodifiableList(result);
      }
    }
  }
}

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