Java tutorial
/* * Copyright (C) 2013 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.collect; import static com.google.common.base.Preconditions.checkNotNull; import static com.google.common.collect.CollectPreconditions.checkNonnegative; import static com.google.common.collect.Maps.newLinkedHashMapWithExpectedSize; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.base.Supplier; import java.io.Serializable; import java.util.ArrayList; import java.util.Collection; import java.util.Comparator; import java.util.EnumMap; import java.util.EnumSet; import java.util.HashMap; import java.util.HashSet; import java.util.LinkedHashMap; import java.util.LinkedHashSet; import java.util.LinkedList; import java.util.List; import java.util.Map; import java.util.Set; import java.util.SortedSet; import java.util.TreeMap; import java.util.TreeSet; import javax.annotation.CheckReturnValue; /** * A builder for a multimap implementation that allows customization of the backing map and value * collection implementations used in a particular multimap. * * <p>This can be used to easily configure multimap data structure implementations not provided * explicitly in {@code com.google.common.collect}, for example: * * <pre> {@code * ListMultimap<String, Integer> treeListMultimap = * MultimapBuilder.treeKeys().arrayListValues().build(); * SetMultimap<Integer, MyEnum> hashEnumMultimap = * MultimapBuilder.hashKeys().enumSetValues(MyEnum.class).build();}</pre> * * <p>{@code MultimapBuilder} instances are immutable. Invoking a configuration method has no * effect on the receiving instance; you must store and use the new builder instance it returns * instead. * * <p>The generated multimaps are serializable if the key and value types are serializable, * unless stated otherwise in one of the configuration methods. * * @author Louis Wasserman * @param <K0> An upper bound on the key type of the generated multimap. * @param <V0> An upper bound on the value type of the generated multimap. * @since 16.0 */ @Beta @GwtCompatible @CheckReturnValue public abstract class MultimapBuilder<K0, V0> { /* * Leaving K and V as upper bounds rather than the actual key and value types allows type * parameters to be left implicit more often. CacheBuilder uses the same technique. */ private MultimapBuilder() { } private static final int DEFAULT_EXPECTED_KEYS = 8; /** * Uses a {@link HashMap} to map keys to value collections. */ public static MultimapBuilderWithKeys<Object> hashKeys() { return hashKeys(DEFAULT_EXPECTED_KEYS); } /** * Uses a {@link HashMap} to map keys to value collections, initialized to expect the specified * number of keys. * * @throws IllegalArgumentException if {@code expectedKeys < 0} */ public static MultimapBuilderWithKeys<Object> hashKeys(final int expectedKeys) { checkNonnegative(expectedKeys, "expectedKeys"); return new MultimapBuilderWithKeys<Object>() { @Override <K, V> Map<K, Collection<V>> createMap() { return Maps.newHashMapWithExpectedSize(expectedKeys); } }; } /** * Uses a {@link LinkedHashMap} to map keys to value collections. * * <p>The collections returned by {@link Multimap#keySet()}, {@link Multimap#keys()}, and * {@link Multimap#asMap()} will iterate through the keys in the order that they were first added * to the multimap, save that if all values associated with a key are removed and then the key is * added back into the multimap, that key will come last in the key iteration order. */ public static MultimapBuilderWithKeys<Object> linkedHashKeys() { return linkedHashKeys(DEFAULT_EXPECTED_KEYS); } /** * Uses a {@link LinkedHashMap} to map keys to value collections, initialized to expect the * specified number of keys. * * <p>The collections returned by {@link Multimap#keySet()}, {@link Multimap#keys()}, and * {@link Multimap#asMap()} will iterate through the keys in the order that they were first added * to the multimap, save that if all values associated with a key are removed and then the key is * added back into the multimap, that key will come last in the key iteration order. */ public static MultimapBuilderWithKeys<Object> linkedHashKeys(final int expectedKeys) { checkNonnegative(expectedKeys, "expectedKeys"); return new MultimapBuilderWithKeys<Object>() { @Override <K, V> Map<K, Collection<V>> createMap() { return newLinkedHashMapWithExpectedSize(expectedKeys); } }; } /** * Uses a naturally-ordered {@link TreeMap} to map keys to value collections. * * <p>The collections returned by {@link Multimap#keySet()}, {@link Multimap#keys()}, and * {@link Multimap#asMap()} will iterate through the keys in sorted order. * * <p>For all multimaps generated by the resulting builder, the {@link Multimap#keySet()} can be * safely cast to a {@link java.util.SortedSet}, and the {@link Multimap#asMap()} can safely be * cast to a {@link java.util.SortedMap}. */ @SuppressWarnings("rawtypes") public static MultimapBuilderWithKeys<Comparable> treeKeys() { return treeKeys(Ordering.natural()); } /** * Uses a {@link TreeMap} sorted by the specified comparator to map keys to value collections. * * <p>The collections returned by {@link Multimap#keySet()}, {@link Multimap#keys()}, and * {@link Multimap#asMap()} will iterate through the keys in sorted order. * * <p>For all multimaps generated by the resulting builder, the {@link Multimap#keySet()} can be * safely cast to a {@link java.util.SortedSet}, and the {@link Multimap#asMap()} can safely be * cast to a {@link java.util.SortedMap}. * * <p>Multimaps generated by the resulting builder will not be serializable if {@code comparator} * is not serializable. */ public static <K0> MultimapBuilderWithKeys<K0> treeKeys(final Comparator<K0> comparator) { checkNotNull(comparator); return new MultimapBuilderWithKeys<K0>() { @Override <K extends K0, V> Map<K, Collection<V>> createMap() { return new TreeMap<K, Collection<V>>(comparator); } }; } /** * Uses an {@link EnumMap} to map keys to value collections. */ public static <K0 extends Enum<K0>> MultimapBuilderWithKeys<K0> enumKeys(final Class<K0> keyClass) { checkNotNull(keyClass); return new MultimapBuilderWithKeys<K0>() { @SuppressWarnings("unchecked") @Override <K extends K0, V> Map<K, Collection<V>> createMap() { // K must actually be K0, since enums are effectively final // (their subclasses are inaccessible) return (Map<K, Collection<V>>) new EnumMap<K0, Collection<V>>(keyClass); } }; } private static final class ArrayListSupplier<V> implements Supplier<List<V>>, Serializable { private final int expectedValuesPerKey; ArrayListSupplier(int expectedValuesPerKey) { this.expectedValuesPerKey = checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); } @Override public List<V> get() { return new ArrayList<V>(expectedValuesPerKey); } } private enum LinkedListSupplier implements Supplier<List<Object>> { INSTANCE; public static <V> Supplier<List<V>> instance() { // Each call generates a fresh LinkedList, which can serve as a List<V> for any V. @SuppressWarnings({ "rawtypes", "unchecked" }) Supplier<List<V>> result = (Supplier) INSTANCE; return result; } @Override public List<Object> get() { return new LinkedList<Object>(); } } private static final class HashSetSupplier<V> implements Supplier<Set<V>>, Serializable { private final int expectedValuesPerKey; HashSetSupplier(int expectedValuesPerKey) { this.expectedValuesPerKey = checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); } @Override public Set<V> get() { return Sets.newHashSetWithExpectedSize(expectedValuesPerKey); } } private static final class LinkedHashSetSupplier<V> implements Supplier<Set<V>>, Serializable { private final int expectedValuesPerKey; LinkedHashSetSupplier(int expectedValuesPerKey) { this.expectedValuesPerKey = checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); } @Override public Set<V> get() { return Sets.newLinkedHashSetWithExpectedSize(expectedValuesPerKey); } } private static final class TreeSetSupplier<V> implements Supplier<SortedSet<V>>, Serializable { private final Comparator<? super V> comparator; TreeSetSupplier(Comparator<? super V> comparator) { this.comparator = checkNotNull(comparator); } @Override public SortedSet<V> get() { return new TreeSet<V>(comparator); } } private static final class EnumSetSupplier<V extends Enum<V>> implements Supplier<Set<V>>, Serializable { private final Class<V> clazz; EnumSetSupplier(Class<V> clazz) { this.clazz = checkNotNull(clazz); } @Override public Set<V> get() { return EnumSet.noneOf(clazz); } } /** * An intermediate stage in a {@link MultimapBuilder} in which the key-value collection map * implementation has been specified, but the value collection implementation has not. * * @param <K0> The upper bound on the key type of the generated multimap. */ public abstract static class MultimapBuilderWithKeys<K0> { private static final int DEFAULT_EXPECTED_VALUES_PER_KEY = 2; MultimapBuilderWithKeys() { } abstract <K extends K0, V> Map<K, Collection<V>> createMap(); /** * Uses an {@link ArrayList} to store value collections. */ public ListMultimapBuilder<K0, Object> arrayListValues() { return arrayListValues(DEFAULT_EXPECTED_VALUES_PER_KEY); } /** * Uses an {@link ArrayList} to store value collections, initialized to expect the specified * number of values per key. * * @throws IllegalArgumentException if {@code expectedValuesPerKey < 0} */ public ListMultimapBuilder<K0, Object> arrayListValues(final int expectedValuesPerKey) { checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); return new ListMultimapBuilder<K0, Object>() { @Override public <K extends K0, V> ListMultimap<K, V> build() { return Multimaps.newListMultimap(MultimapBuilderWithKeys.this.<K, V>createMap(), new ArrayListSupplier<V>(expectedValuesPerKey)); } }; } /** * Uses a {@link LinkedList} to store value collections. */ public ListMultimapBuilder<K0, Object> linkedListValues() { return new ListMultimapBuilder<K0, Object>() { @Override public <K extends K0, V> ListMultimap<K, V> build() { return Multimaps.newListMultimap(MultimapBuilderWithKeys.this.<K, V>createMap(), LinkedListSupplier.<V>instance()); } }; } /** * Uses a {@link HashSet} to store value collections. */ public SetMultimapBuilder<K0, Object> hashSetValues() { return hashSetValues(DEFAULT_EXPECTED_VALUES_PER_KEY); } /** * Uses a {@link HashSet} to store value collections, initialized to expect the specified number * of values per key. * * @throws IllegalArgumentException if {@code expectedValuesPerKey < 0} */ public SetMultimapBuilder<K0, Object> hashSetValues(final int expectedValuesPerKey) { checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); return new SetMultimapBuilder<K0, Object>() { @Override public <K extends K0, V> SetMultimap<K, V> build() { return Multimaps.newSetMultimap(MultimapBuilderWithKeys.this.<K, V>createMap(), new HashSetSupplier<V>(expectedValuesPerKey)); } }; } /** * Uses a {@link LinkedHashSet} to store value collections. */ public SetMultimapBuilder<K0, Object> linkedHashSetValues() { return linkedHashSetValues(DEFAULT_EXPECTED_VALUES_PER_KEY); } /** * Uses a {@link LinkedHashSet} to store value collections, initialized to expect the specified * number of values per key. * * @throws IllegalArgumentException if {@code expectedValuesPerKey < 0} */ public SetMultimapBuilder<K0, Object> linkedHashSetValues(final int expectedValuesPerKey) { checkNonnegative(expectedValuesPerKey, "expectedValuesPerKey"); return new SetMultimapBuilder<K0, Object>() { @Override public <K extends K0, V> SetMultimap<K, V> build() { return Multimaps.newSetMultimap(MultimapBuilderWithKeys.this.<K, V>createMap(), new LinkedHashSetSupplier<V>(expectedValuesPerKey)); } }; } /** * Uses a naturally-ordered {@link TreeSet} to store value collections. */ @SuppressWarnings("rawtypes") public SortedSetMultimapBuilder<K0, Comparable> treeSetValues() { return treeSetValues(Ordering.natural()); } /** * Uses a {@link TreeSet} ordered by the specified comparator to store value collections. * * <p>Multimaps generated by the resulting builder will not be serializable if * {@code comparator} is not serializable. */ public <V0> SortedSetMultimapBuilder<K0, V0> treeSetValues(final Comparator<V0> comparator) { checkNotNull(comparator, "comparator"); return new SortedSetMultimapBuilder<K0, V0>() { @Override public <K extends K0, V extends V0> SortedSetMultimap<K, V> build() { return Multimaps.newSortedSetMultimap(MultimapBuilderWithKeys.this.<K, V>createMap(), new TreeSetSupplier<V>(comparator)); } }; } /** * Uses an {@link EnumSet} to store value collections. */ public <V0 extends Enum<V0>> SetMultimapBuilder<K0, V0> enumSetValues(final Class<V0> valueClass) { checkNotNull(valueClass, "valueClass"); return new SetMultimapBuilder<K0, V0>() { @Override public <K extends K0, V extends V0> SetMultimap<K, V> build() { // V must actually be V0, since enums are effectively final // (their subclasses are inaccessible) @SuppressWarnings({ "unchecked", "rawtypes" }) Supplier<Set<V>> factory = (Supplier) new EnumSetSupplier<V0>(valueClass); return Multimaps.newSetMultimap(MultimapBuilderWithKeys.this.<K, V>createMap(), factory); } }; } } /** * Returns a new, empty {@code Multimap} with the specified implementation. */ public abstract <K extends K0, V extends V0> Multimap<K, V> build(); /** * Returns a {@code Multimap} with the specified implementation, initialized with the entries of * {@code multimap}. */ public <K extends K0, V extends V0> Multimap<K, V> build(Multimap<? extends K, ? extends V> multimap) { Multimap<K, V> result = build(); result.putAll(multimap); return result; } /** * A specialization of {@link MultimapBuilder} that generates {@link ListMultimap} instances. */ public abstract static class ListMultimapBuilder<K0, V0> extends MultimapBuilder<K0, V0> { ListMultimapBuilder() { } @Override public abstract <K extends K0, V extends V0> ListMultimap<K, V> build(); @Override public <K extends K0, V extends V0> ListMultimap<K, V> build(Multimap<? extends K, ? extends V> multimap) { return (ListMultimap<K, V>) super.build(multimap); } } /** * A specialization of {@link MultimapBuilder} that generates {@link SetMultimap} instances. */ public abstract static class SetMultimapBuilder<K0, V0> extends MultimapBuilder<K0, V0> { SetMultimapBuilder() { } @Override public abstract <K extends K0, V extends V0> SetMultimap<K, V> build(); @Override public <K extends K0, V extends V0> SetMultimap<K, V> build(Multimap<? extends K, ? extends V> multimap) { return (SetMultimap<K, V>) super.build(multimap); } } /** * A specialization of {@link MultimapBuilder} that generates {@link SortedSetMultimap} instances. */ public abstract static class SortedSetMultimapBuilder<K0, V0> extends SetMultimapBuilder<K0, V0> { SortedSetMultimapBuilder() { } @Override public abstract <K extends K0, V extends V0> SortedSetMultimap<K, V> build(); @Override public <K extends K0, V extends V0> SortedSetMultimap<K, V> build( Multimap<? extends K, ? extends V> multimap) { return (SortedSetMultimap<K, V>) super.build(multimap); } } }