trunk/src/com/google/common/collect/ImmutableSetMultimap.java - platform/external/guava - Git at Google

 /*
  * Copyright (C) 2009 Google 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 com.google.common.collect;

 import com.google.common.annotations.GwtCompatible;
 import static com.google.common.base.Preconditions.checkNotNull;

 import java.io.IOException;
 import java.io.InvalidObjectException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.Map;

 import javax.annotation.Nullable;

 /**
  * An immutable {@link SetMultimap} with reliable user-specified key and value
  * iteration order. Does not permit null keys or values.
  *
  * <p>Unlike {@link Multimaps#unmodifiableSetMultimap(SetMultimap)}, which is
  * a <i>view</i> of a separate multimap which can still change, an instance of
  * {@code ImmutableSetMultimap} contains its own data and will <i>never</i>
  * change. {@code ImmutableSetMultimap} is convenient for
  * {@code public static final} multimaps ("constant multimaps") and also lets
  * you easily make a "defensive copy" of a multimap provided to your class by
  * a caller.
  *
  * <p><b>Note</b>: Although this class is not final, it cannot be subclassed as
  * it has no public or protected constructors. Thus, instances of this class
  * are guaranteed to be immutable.
  *
  * @author Mike Ward
  * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
  */
 @GwtCompatible(serializable = true)
 public class ImmutableSetMultimap<K, V>
     extends ImmutableMultimap<K, V>
     implements SetMultimap<K, V> {

   /** Returns the empty multimap. */
   // Casting is safe because the multimap will never hold any elements.
   @SuppressWarnings("unchecked")
   public static <K, V> ImmutableSetMultimap<K, V> of() {
     return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
   }

   /**
    * Returns an immutable multimap containing a single entry.
    */
   public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1) {
     ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
     builder.put(k1, v1);
     return builder.build();
   }

   /**
    * Returns an immutable multimap containing the given entries, in order.
    * Repeated occurrences of an entry (according to {@link Object#equals}) after
    * the first are ignored.
    */
   public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2) {
     ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
     builder.put(k1, v1);
     builder.put(k2, v2);
     return builder.build();
   }

   /**
    * Returns an immutable multimap containing the given entries, in order.
    * Repeated occurrences of an entry (according to {@link Object#equals}) after
    * the first are ignored.
    */
   public static <K, V> ImmutableSetMultimap<K, V> of(
       K k1, V v1, K k2, V v2, K k3, V v3) {
     ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
     builder.put(k1, v1);
     builder.put(k2, v2);
     builder.put(k3, v3);
     return builder.build();
   }

   /**
    * Returns an immutable multimap containing the given entries, in order.
    * Repeated occurrences of an entry (according to {@link Object#equals}) after
    * the first are ignored.
    */
   public static <K, V> ImmutableSetMultimap<K, V> of(
       K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
     ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
     builder.put(k1, v1);
     builder.put(k2, v2);
     builder.put(k3, v3);
     builder.put(k4, v4);
     return builder.build();
   }

   /**
    * Returns an immutable multimap containing the given entries, in order.
    * Repeated occurrences of an entry (according to {@link Object#equals}) after
    * the first are ignored.
    */
   public static <K, V> ImmutableSetMultimap<K, V> of(
       K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
     ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
     builder.put(k1, v1);
     builder.put(k2, v2);
     builder.put(k3, v3);
     builder.put(k4, v4);
     builder.put(k5, v5);
     return builder.build();
   }

   // looking for of() with > 5 entries? Use the builder instead.

   /**
    * Returns a new {@link Builder}.
    */
   public static <K, V> Builder<K, V> builder() {
     return new Builder<K, V>();
   }

   /**
    * Multimap for {@link ImmutableSetMultimap.Builder} that maintains key
    * and value orderings and performs better than {@link LinkedHashMultimap}.
    */
   private static class BuilderMultimap<K, V> extends AbstractMultimap<K, V> {
     BuilderMultimap() {
       super(new LinkedHashMap<K, Collection<V>>());
     }
     @Override Collection<V> createCollection() {
       return Sets.newLinkedHashSet();
     }
     private static final long serialVersionUID = 0;
   }

   /**
    * A builder for creating immutable {@code SetMultimap} instances, especially
    * {@code public static final} multimaps ("constant multimaps"). Example:
    * <pre>   {@code
    *
    *   static final Multimap<String, Integer> STRING_TO_INTEGER_MULTIMAP =
    *       new ImmutableSetMultimap.Builder<String, Integer>()
    *           .put("one", 1)
    *           .putAll("several", 1, 2, 3)
    *           .putAll("many", 1, 2, 3, 4, 5)
    *           .build();}</pre>
    *
    * <p>Builder instances can be reused - it is safe to call {@link #build}
    * multiple times to build multiple multimaps in series. Each multimap
    * contains the key-value mappings in the previously created multimaps.
    */
   public static final class Builder<K, V>
       extends ImmutableMultimap.Builder<K, V> {
     private final Multimap<K, V> builderMultimap = new BuilderMultimap<K, V>();

     /**
      * Creates a new builder. The returned builder is equivalent to the builder
      * generated by {@link ImmutableSetMultimap#builder}.
      */
     public Builder() {}

     /**
      * Adds a key-value mapping to the built multimap if it is not already
      * present.
      */
     @Override public Builder<K, V> put(K key, V value) {
       builderMultimap.put(checkNotNull(key), checkNotNull(value));
       return this;
     }

     /**
      * Stores a collection of values with the same key in the built multimap.
      *
      * @throws NullPointerException if {@code key}, {@code values}, or any
      *     element in {@code values} is null. The builder is left in an invalid
      *     state.
      */
     @Override public Builder<K, V> putAll(K key, Iterable<? extends V> values) {
       Collection<V> collection = builderMultimap.get(checkNotNull(key));
       for (V value : values) {
         collection.add(checkNotNull(value));
       }
       return this;
     }

     /**
      * Stores an array of values with the same key in the built multimap.
      *
      * @throws NullPointerException if the key or any value is null. The
      *     builder is left in an invalid state.
      */
     @Override public Builder<K, V> putAll(K key, V... values) {
       return putAll(key, Arrays.asList(values));
     }

     /**
      * Stores another multimap's entries in the built multimap. The generated
      * multimap's key and value orderings correspond to the iteration ordering
      * of the {@code multimap.asMap()} view, with new keys and values following
      * any existing keys and values.
      *
      * @throws NullPointerException if any key or value in {@code multimap} is
      *     null. The builder is left in an invalid state.
      */
     @Override public Builder<K, V> putAll(
         Multimap<? extends K, ? extends V> multimap) {
       for (Map.Entry<? extends K, ? extends Collection<? extends V>> entry
           : multimap.asMap().entrySet()) {
         putAll(entry.getKey(), entry.getValue());
       }
       return this;
     }

     /**
      * Returns a newly-created immutable set multimap.
      */
     @Override public ImmutableSetMultimap<K, V> build() {
       return copyOf(builderMultimap);
     }
   }

   /**
    * Returns an immutable set multimap containing the same mappings as
    * {@code multimap}. The generated multimap's key and value orderings
    * correspond to the iteration ordering of the {@code multimap.asMap()} view.
    * Repeated occurrences of an entry in the multimap after the first are
    * ignored.
    *
    * <p><b>Note:</b> Despite what the method name suggests, if
    * {@code multimap} is an {@code ImmutableSetMultimap}, no copy will actually
    * be performed, and the given multimap itself will be returned.
    *
    * @throws NullPointerException if any key or value in {@code multimap} is
    *     null
    */
   public static <K, V> ImmutableSetMultimap<K, V> copyOf(
       Multimap<? extends K, ? extends V> multimap) {
     if (multimap.isEmpty()) {
       return of();
     }

     if (multimap instanceof ImmutableSetMultimap) {
       @SuppressWarnings("unchecked") // safe since multimap is not writable
       ImmutableSetMultimap<K, V> kvMultimap
           = (ImmutableSetMultimap<K, V>) multimap;
       return kvMultimap;
     }

     ImmutableMap.Builder<K, ImmutableSet<V>> builder = ImmutableMap.builder();
     int size = 0;

     for (Map.Entry<? extends K, ? extends Collection<? extends V>> entry
         : multimap.asMap().entrySet()) {
       K key = entry.getKey();
       Collection<? extends V> values = entry.getValue();
       ImmutableSet<V> set = ImmutableSet.copyOf(values);
       if (!set.isEmpty()) {
         builder.put(key, set);
         size += set.size();
       }
     }

     return new ImmutableSetMultimap<K, V>(builder.build(), size);
   }

   ImmutableSetMultimap(ImmutableMap<K, ImmutableSet<V>> map, int size) {
     super(map, size);
   }

   // views

   /**
    * Returns an immutable set of the values for the given key.  If no mappings
    * in the multimap have the provided key, an empty immutable set is returned.
    * The values are in the same order as the parameters used to build this
    * multimap.
    */
   @Override public ImmutableSet<V> get(@Nullable K key) {
     // This cast is safe as its type is known in constructor.
     ImmutableSet<V> set = (ImmutableSet<V>) map.get(key);
     return (set == null) ? ImmutableSet.<V>of() : set;
   }

   /**
    * Guaranteed to throw an exception and leave the multimap unmodified.
    *
    * @throws UnsupportedOperationException always
    */
   @Override public ImmutableSet<V> removeAll(Object key) {
     throw new UnsupportedOperationException();
   }

   /**
    * Guaranteed to throw an exception and leave the multimap unmodified.
    *
    * @throws UnsupportedOperationException always
    */
   @Override public ImmutableSet<V> replaceValues(
       K key, Iterable<? extends V> values) {
     throw new UnsupportedOperationException();
   }

   private transient ImmutableSet<Map.Entry<K, V>> entries;

   /**
    * Returns an immutable collection of all key-value pairs in the multimap.
    * Its iterator traverses the values for the first key, the values for the
    * second key, and so on.
    */
   // TODO: Fix this so that two copies of the entries are not created.
   @Override public ImmutableSet<Map.Entry<K, V>> entries() {
     ImmutableSet<Map.Entry<K, V>> result = entries;
     return (result == null)
         ? (entries = ImmutableSet.copyOf(super.entries()))
         : result;
   }

   /**
    * @serialData number of distinct keys, and then for each distinct key: the
    *     key, the number of values for that key, and the key's values
    */
   private void writeObject(ObjectOutputStream stream) throws IOException {
     stream.defaultWriteObject();
     Serialization.writeMultimap(this, stream);
   }

   private void readObject(ObjectInputStream stream)
       throws IOException, ClassNotFoundException {
     stream.defaultReadObject();
     int keyCount = stream.readInt();
     if (keyCount < 0) {
       throw new InvalidObjectException("Invalid key count " + keyCount);
     }
     ImmutableMap.Builder<Object, ImmutableSet<Object>> builder
         = ImmutableMap.builder();
     int tmpSize = 0;

     for (int i = 0; i < keyCount; i++) {
       Object key = stream.readObject();
       int valueCount = stream.readInt();
       if (valueCount <= 0) {
         throw new InvalidObjectException("Invalid value count " + valueCount);
       }

       Object[] array = new Object[valueCount];
       for (int j = 0; j < valueCount; j++) {
         array[j] = stream.readObject();
       }
       ImmutableSet<Object> valueSet = ImmutableSet.of(array);
       if (valueSet.size() != array.length) {
         throw new InvalidObjectException(
             "Duplicate key-value pairs exist for key " + key);
       }
       builder.put(key, valueSet);
       tmpSize += valueCount;
     }

     ImmutableMap<Object, ImmutableSet<Object>> tmpMap;
     try {
       tmpMap = builder.build();
     } catch (IllegalArgumentException e) {
       throw (InvalidObjectException)
           new InvalidObjectException(e.getMessage()).initCause(e);
     }

     FieldSettersHolder.MAP_FIELD_SETTER.set(this, tmpMap);
     FieldSettersHolder.SIZE_FIELD_SETTER.set(this, tmpSize);
   }

   private static final long serialVersionUID = 0;
 }
	/*
	* Copyright (C) 2009 Google 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 com.google.common.collect;

	import com.google.common.annotations.GwtCompatible;
	import static com.google.common.base.Preconditions.checkNotNull;

	import java.io.IOException;
	import java.io.InvalidObjectException;
	import java.io.ObjectInputStream;
	import java.io.ObjectOutputStream;
	import java.util.Arrays;
	import java.util.Collection;
	import java.util.LinkedHashMap;
	import java.util.Map;

	import javax.annotation.Nullable;

	/**
	* An immutable {@link SetMultimap} with reliable user-specified key and value
	* iteration order. Does not permit null keys or values.
	*
	* <p>Unlike {@link Multimaps#unmodifiableSetMultimap(SetMultimap)}, which is
	* a <i>view</i> of a separate multimap which can still change, an instance of
	* {@code ImmutableSetMultimap} contains its own data and will <i>never</i>
	* change. {@code ImmutableSetMultimap} is convenient for
	* {@code public static final} multimaps ("constant multimaps") and also lets
	* you easily make a "defensive copy" of a multimap provided to your class by
	* a caller.
	*
	* <p><b>Note</b>: Although this class is not final, it cannot be subclassed as
	* it has no public or protected constructors. Thus, instances of this class
	* are guaranteed to be immutable.
	*
	* @author Mike Ward
	* @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
	*/
	@GwtCompatible(serializable = true)
	public class ImmutableSetMultimap<K, V>
	extends ImmutableMultimap<K, V>
	implements SetMultimap<K, V> {

	/** Returns the empty multimap. */
	// Casting is safe because the multimap will never hold any elements.
	@SuppressWarnings("unchecked")
	public static <K, V> ImmutableSetMultimap<K, V> of() {
	return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
	}

	/**
	* Returns an immutable multimap containing a single entry.
	*/
	public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1) {
	ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
	builder.put(k1, v1);
	return builder.build();
	}

	/**
	* Returns an immutable multimap containing the given entries, in order.
	* Repeated occurrences of an entry (according to {@link Object#equals}) after
	* the first are ignored.
	*/
	public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2) {
	ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
	builder.put(k1, v1);
	builder.put(k2, v2);
	return builder.build();
	}

	/**
	* Returns an immutable multimap containing the given entries, in order.
	* Repeated occurrences of an entry (according to {@link Object#equals}) after
	* the first are ignored.
	*/
	public static <K, V> ImmutableSetMultimap<K, V> of(
	K k1, V v1, K k2, V v2, K k3, V v3) {
	ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
	builder.put(k1, v1);
	builder.put(k2, v2);
	builder.put(k3, v3);
	return builder.build();
	}

	/**
	* Returns an immutable multimap containing the given entries, in order.
	* Repeated occurrences of an entry (according to {@link Object#equals}) after
	* the first are ignored.
	*/
	public static <K, V> ImmutableSetMultimap<K, V> of(
	K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
	ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
	builder.put(k1, v1);
	builder.put(k2, v2);
	builder.put(k3, v3);
	builder.put(k4, v4);
	return builder.build();
	}

	/**
	* Returns an immutable multimap containing the given entries, in order.
	* Repeated occurrences of an entry (according to {@link Object#equals}) after
	* the first are ignored.
	*/
	public static <K, V> ImmutableSetMultimap<K, V> of(
	K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
	ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
	builder.put(k1, v1);
	builder.put(k2, v2);
	builder.put(k3, v3);
	builder.put(k4, v4);
	builder.put(k5, v5);
	return builder.build();
	}

	// looking for of() with > 5 entries? Use the builder instead.

	/**
	* Returns a new {@link Builder}.
	*/
	public static <K, V> Builder<K, V> builder() {
	return new Builder<K, V>();
	}

	/**
	* Multimap for {@link ImmutableSetMultimap.Builder} that maintains key
	* and value orderings and performs better than {@link LinkedHashMultimap}.
	*/
	private static class BuilderMultimap<K, V> extends AbstractMultimap<K, V> {
	BuilderMultimap() {
	super(new LinkedHashMap<K, Collection<V>>());
	}
	@Override Collection<V> createCollection() {
	return Sets.newLinkedHashSet();
	}
	private static final long serialVersionUID = 0;
	}

	/**
	* A builder for creating immutable {@code SetMultimap} instances, especially
	* {@code public static final} multimaps ("constant multimaps"). Example:
	* <pre> {@code
	*
	* static final Multimap<String, Integer> STRING_TO_INTEGER_MULTIMAP =
	* new ImmutableSetMultimap.Builder<String, Integer>()
	* .put("one", 1)
	* .putAll("several", 1, 2, 3)
	* .putAll("many", 1, 2, 3, 4, 5)
	* .build();}</pre>
	*
	* <p>Builder instances can be reused - it is safe to call {@link #build}
	* multiple times to build multiple multimaps in series. Each multimap
	* contains the key-value mappings in the previously created multimaps.
	*/
	public static final class Builder<K, V>
	extends ImmutableMultimap.Builder<K, V> {
	private final Multimap<K, V> builderMultimap = new BuilderMultimap<K, V>();

	/**
	* Creates a new builder. The returned builder is equivalent to the builder
	* generated by {@link ImmutableSetMultimap#builder}.
	*/
	public Builder() {}

	/**
	* Adds a key-value mapping to the built multimap if it is not already
	* present.
	*/
	@Override public Builder<K, V> put(K key, V value) {
	builderMultimap.put(checkNotNull(key), checkNotNull(value));
	return this;
	}

	/**
	* Stores a collection of values with the same key in the built multimap.
	*
	* @throws NullPointerException if {@code key}, {@code values}, or any
	* element in {@code values} is null. The builder is left in an invalid
	* state.
	*/
	@Override public Builder<K, V> putAll(K key, Iterable<? extends V> values) {
	Collection<V> collection = builderMultimap.get(checkNotNull(key));
	for (V value : values) {
	collection.add(checkNotNull(value));
	}
	return this;
	}

	/**
	* Stores an array of values with the same key in the built multimap.
	*
	* @throws NullPointerException if the key or any value is null. The
	* builder is left in an invalid state.
	*/
	@Override public Builder<K, V> putAll(K key, V... values) {
	return putAll(key, Arrays.asList(values));
	}

	/**
	* Stores another multimap's entries in the built multimap. The generated
	* multimap's key and value orderings correspond to the iteration ordering
	* of the {@code multimap.asMap()} view, with new keys and values following
	* any existing keys and values.
	*
	* @throws NullPointerException if any key or value in {@code multimap} is
	* null. The builder is left in an invalid state.
	*/
	@Override public Builder<K, V> putAll(
	Multimap<? extends K, ? extends V> multimap) {
	for (Map.Entry<? extends K, ? extends Collection<? extends V>> entry
	: multimap.asMap().entrySet()) {
	putAll(entry.getKey(), entry.getValue());
	}
	return this;
	}

	/**
	* Returns a newly-created immutable set multimap.
	*/
	@Override public ImmutableSetMultimap<K, V> build() {
	return copyOf(builderMultimap);
	}
	}

	/**
	* Returns an immutable set multimap containing the same mappings as
	* {@code multimap}. The generated multimap's key and value orderings
	* correspond to the iteration ordering of the {@code multimap.asMap()} view.
	* Repeated occurrences of an entry in the multimap after the first are
	* ignored.
	*
	* <p><b>Note:</b> Despite what the method name suggests, if
	* {@code multimap} is an {@code ImmutableSetMultimap}, no copy will actually
	* be performed, and the given multimap itself will be returned.
	*
	* @throws NullPointerException if any key or value in {@code multimap} is
	* null
	*/
	public static <K, V> ImmutableSetMultimap<K, V> copyOf(
	Multimap<? extends K, ? extends V> multimap) {
	if (multimap.isEmpty()) {
	return of();
	}

	if (multimap instanceof ImmutableSetMultimap) {
	@SuppressWarnings("unchecked") // safe since multimap is not writable
	ImmutableSetMultimap<K, V> kvMultimap
	= (ImmutableSetMultimap<K, V>) multimap;
	return kvMultimap;
	}

	ImmutableMap.Builder<K, ImmutableSet<V>> builder = ImmutableMap.builder();
	int size = 0;

	for (Map.Entry<? extends K, ? extends Collection<? extends V>> entry
	: multimap.asMap().entrySet()) {
	K key = entry.getKey();
	Collection<? extends V> values = entry.getValue();
	ImmutableSet<V> set = ImmutableSet.copyOf(values);
	if (!set.isEmpty()) {
	builder.put(key, set);
	size += set.size();
	}
	}

	return new ImmutableSetMultimap<K, V>(builder.build(), size);
	}

	ImmutableSetMultimap(ImmutableMap<K, ImmutableSet<V>> map, int size) {
	super(map, size);
	}

	// views

	/**
	* Returns an immutable set of the values for the given key. If no mappings
	* in the multimap have the provided key, an empty immutable set is returned.
	* The values are in the same order as the parameters used to build this
	* multimap.
	*/
	@Override public ImmutableSet<V> get(@Nullable K key) {
	// This cast is safe as its type is known in constructor.
	ImmutableSet<V> set = (ImmutableSet<V>) map.get(key);
	return (set == null) ? ImmutableSet.<V>of() : set;
	}

	/**
	* Guaranteed to throw an exception and leave the multimap unmodified.
	*
	* @throws UnsupportedOperationException always
	*/
	@Override public ImmutableSet<V> removeAll(Object key) {
	throw new UnsupportedOperationException();
	}

	/**
	* Guaranteed to throw an exception and leave the multimap unmodified.
	*
	* @throws UnsupportedOperationException always
	*/
	@Override public ImmutableSet<V> replaceValues(
	K key, Iterable<? extends V> values) {
	throw new UnsupportedOperationException();
	}

	private transient ImmutableSet<Map.Entry<K, V>> entries;

	/**
	* Returns an immutable collection of all key-value pairs in the multimap.
	* Its iterator traverses the values for the first key, the values for the
	* second key, and so on.
	*/
	// TODO: Fix this so that two copies of the entries are not created.
	@Override public ImmutableSet<Map.Entry<K, V>> entries() {
	ImmutableSet<Map.Entry<K, V>> result = entries;
	return (result == null)
	? (entries = ImmutableSet.copyOf(super.entries()))
	: result;
	}

	/**
	* @serialData number of distinct keys, and then for each distinct key: the
	* key, the number of values for that key, and the key's values
	*/
	private void writeObject(ObjectOutputStream stream) throws IOException {
	stream.defaultWriteObject();
	Serialization.writeMultimap(this, stream);
	}

	private void readObject(ObjectInputStream stream)
	throws IOException, ClassNotFoundException {
	stream.defaultReadObject();
	int keyCount = stream.readInt();
	if (keyCount < 0) {
	throw new InvalidObjectException("Invalid key count " + keyCount);
	}
	ImmutableMap.Builder<Object, ImmutableSet<Object>> builder
	= ImmutableMap.builder();
	int tmpSize = 0;

	for (int i = 0; i < keyCount; i++) {
	Object key = stream.readObject();
	int valueCount = stream.readInt();
	if (valueCount <= 0) {
	throw new InvalidObjectException("Invalid value count " + valueCount);
	}

	Object[] array = new Object[valueCount];
	for (int j = 0; j < valueCount; j++) {
	array[j] = stream.readObject();
	}
	ImmutableSet<Object> valueSet = ImmutableSet.of(array);
	if (valueSet.size() != array.length) {
	throw new InvalidObjectException(
	"Duplicate key-value pairs exist for key " + key);
	}
	builder.put(key, valueSet);
	tmpSize += valueCount;
	}

	ImmutableMap<Object, ImmutableSet<Object>> tmpMap;
	try {
	tmpMap = builder.build();
	} catch (IllegalArgumentException e) {
	throw (InvalidObjectException)
	new InvalidObjectException(e.getMessage()).initCause(e);
	}

	FieldSettersHolder.MAP_FIELD_SETTER.set(this, tmpMap);
	FieldSettersHolder.SIZE_FIELD_SETTER.set(this, tmpSize);
	}

	private static final long serialVersionUID = 0;
	}