common/collect/RegularImmutableMap.java

/*
* Copyright (C) 2008 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.collect.CollectPreconditions.checkEntryNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.ImmutableMapEntry.TerminalEntry;

import javax.annotation.Nullable;

/**
 * Implementation of {@link ImmutableMap} with two or more entries.
 *
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 * @author Gregory Kick
 */
@GwtCompatible(serializable = true, emulated = true)
final class RegularImmutableMap<K, V> extends ImmutableMap<K, V> {

  // entries in insertion order
  private final transient ImmutableMapEntry<K, V>[] entries;
  // array of linked lists of entries
  private final transient ImmutableMapEntry<K, V>[] table;
  // 'and' with an int to get a table index
  private final transient int mask;

  RegularImmutableMap(TerminalEntry<?, ?>... theEntries) {
    this(theEntries.length, theEntries);
  }

  /**
   * Constructor for RegularImmutableMap that takes as input an array of {@code TerminalEntry}
   * entries.  Assumes that these entries have already been checked for null.
   *
   * <p>This allows reuse of the entry objects from the array in the actual implementation.
   */
  RegularImmutableMap(int size, TerminalEntry<?, ?>[] theEntries) {
    entries = createEntryArray(size);
    int tableSize = Hashing.closedTableSize(size, MAX_LOAD_FACTOR);
    table = createEntryArray(tableSize);
    mask = tableSize - 1;
    for (int entryIndex = 0; entryIndex < size; entryIndex++) {
      @SuppressWarnings("unchecked")
      TerminalEntry<K, V> entry = (TerminalEntry<K, V>) theEntries[entryIndex];
      K key = entry.getKey();
      int tableIndex = Hashing.smear(key.hashCode()) & mask;
      @Nullable ImmutableMapEntry<K, V> existing = table[tableIndex];
      // prepend, not append, so the entries can be immutable
      ImmutableMapEntry<K, V> newEntry = (existing == null)
          ? entry
          : new NonTerminalMapEntry<K, V>(entry, existing);
      table[tableIndex] = newEntry;
      entries[entryIndex] = newEntry;
      checkNoConflictInBucket(key, newEntry, existing);
    }
  }

  /**
   * Constructor for RegularImmutableMap that makes no assumptions about the input entries.
   */
  RegularImmutableMap(Entry<?, ?>[] theEntries) {
    int size = theEntries.length;
    entries = createEntryArray(size);
    int tableSize = Hashing.closedTableSize(size, MAX_LOAD_FACTOR);
    table = createEntryArray(tableSize);
    mask = tableSize - 1;
    for (int entryIndex = 0; entryIndex < size; entryIndex++) {
      @SuppressWarnings("unchecked") // all our callers carefully put in only Entry<K, V>s
      Entry<K, V> entry = (Entry<K, V>) theEntries[entryIndex];
      K key = entry.getKey();
      V value = entry.getValue();
      checkEntryNotNull(key, value);
      int tableIndex = Hashing.smear(key.hashCode()) & mask;
      @Nullable ImmutableMapEntry<K, V> existing = table[tableIndex];
      // prepend, not append, so the entries can be immutable
      ImmutableMapEntry<K, V> newEntry = (existing == null)
          ? new TerminalEntry<K, V>(key, value)
          : new NonTerminalMapEntry<K, V>(key, value, existing);
      table[tableIndex] = newEntry;
      entries[entryIndex] = newEntry;
      checkNoConflictInBucket(key, newEntry, existing);
    }
  }

  private void checkNoConflictInBucket(
      K key, ImmutableMapEntry<K, V> entry, ImmutableMapEntry<K, V> bucketHead) {
    for (; bucketHead != null; bucketHead = bucketHead.getNextInKeyBucket()) {
      checkNoConflict(!key.equals(bucketHead.getKey()), "key", entry, bucketHead);
    }
  }

  private static final class NonTerminalMapEntry<K, V> extends ImmutableMapEntry<K, V> {
    private final ImmutableMapEntry<K, V> nextInKeyBucket;

    NonTerminalMapEntry(K key, V value, ImmutableMapEntry<K, V> nextInKeyBucket) {
      super(key, value);
      this.nextInKeyBucket = nextInKeyBucket;
    }

    NonTerminalMapEntry(ImmutableMapEntry<K, V> contents, ImmutableMapEntry<K, V> nextInKeyBucket) {
      super(contents);
      this.nextInKeyBucket = nextInKeyBucket;
    }

    @Override
    ImmutableMapEntry<K, V> getNextInKeyBucket() {
      return nextInKeyBucket;
    }

    @Override
    @Nullable
    ImmutableMapEntry<K, V> getNextInValueBucket() {
      return null;
    }

  }

  /**
   * Closed addressing tends to perform well even with high load factors.
   * Being conservative here ensures that the table is still likely to be
   * relatively sparse (hence it misses fast) while saving space.
   */
  private static final double MAX_LOAD_FACTOR = 1.2;

  /**
   * Creates an {@code ImmutableMapEntry} array to hold parameterized entries. The
   * result must never be upcast back to ImmutableMapEntry[] (or Object[], etc.), or
   * allowed to escape the class.
   */
  @SuppressWarnings("unchecked") // Safe as long as the javadocs are followed
  private ImmutableMapEntry<K, V>[] createEntryArray(int size) {
    return new ImmutableMapEntry[size];
  }

  @Override public V get(@Nullable Object key) {
    if (key == null) {
      return null;
    }
    int index = Hashing.smear(key.hashCode()) & mask;
    for (ImmutableMapEntry<K, V> entry = table[index];
        entry != null;
        entry = entry.getNextInKeyBucket()) {
      K candidateKey = entry.getKey();

      /*
       * Assume that equals uses the == optimization when appropriate, and that
       * it would check hash codes as an optimization when appropriate. If we
       * did these things, it would just make things worse for the most
       * performance-conscious users.
       */
      if (key.equals(candidateKey)) {
        return entry.getValue();
      }
    }
    return null;
  }

  @Override
  public int size() {
    return entries.length;
  }

  @Override boolean isPartialView() {
    return false;
  }

  @Override
  ImmutableSet<Entry<K, V>> createEntrySet() {
    return new EntrySet();
  }

  @SuppressWarnings("serial") // uses writeReplace(), not default serialization
  private class EntrySet extends ImmutableMapEntrySet<K, V> {
    @Override ImmutableMap<K, V> map() {
      return RegularImmutableMap.this;
    }

    @Override
    public UnmodifiableIterator<Entry<K, V>> iterator() {
      return asList().iterator();
    }

    @Override
    ImmutableList<Entry<K, V>> createAsList() {
      return new RegularImmutableAsList<Entry<K, V>>(this, entries);
    }
  }

  // This class is never actually serialized directly, but we have to make the
  // warning go away (and suppressing would suppress for all nested classes too)
  private static final long serialVersionUID = 0;
}