Java example source code file (RegularImmutableMap.java)

This example Java source code file (RegularImmutableMap.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

annotation, entry, gwtcompatible, immutablemapentry, immutableset, max_load_factor, nonterminalimmutablemapentry, nullable, object, override, regularimmutablemap

The RegularImmutableMap.java Java example source code

/*
 * 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.base.Preconditions.checkPositionIndex;
import static com.google.common.collect.CollectPreconditions.checkEntryNotNull;
import static com.google.common.collect.ImmutableMapEntry.createEntryArray;

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

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 {

  // entries in insertion order
  private final transient Entry<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;

  static <K, V> RegularImmutableMap fromEntries(Entry... entries) {
    return fromEntryArray(entries.length, entries);
  }

  /**
   * Creates a RegularImmutableMap from the first n entries in entryArray.  This implementation
   * may replace the entries in entryArray with its own entry objects (though they will have the
   * same key/value contents), and may take ownership of entryArray.
   */
  static <K, V> RegularImmutableMap fromEntryArray(int n, Entry[] entryArray) {
    checkPositionIndex(n, entryArray.length);
    Entry<K, V>[] entries;
    if (n == entryArray.length) {
      entries = entryArray;
    } else {
      entries = createEntryArray(n);
    }
    int tableSize = Hashing.closedTableSize(n, MAX_LOAD_FACTOR);
    ImmutableMapEntry<K, V>[] table = createEntryArray(tableSize);
    int mask = tableSize - 1;
    for (int entryIndex = 0; entryIndex < n; entryIndex++) {
      Entry<K, V> entry = entryArray[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;
      if (existing == null) {
        boolean reusable =
            entry instanceof ImmutableMapEntry && ((ImmutableMapEntry<K, V>) entry).isReusable();
        newEntry =
            reusable ? (ImmutableMapEntry<K, V>) entry : new ImmutableMapEntry(key, value);
      } else {
        newEntry = new NonTerminalImmutableMapEntry<K, V>(key, value, existing);
      }
      table[tableIndex] = newEntry;
      entries[entryIndex] = newEntry;
      checkNoConflictInKeyBucket(key, newEntry, existing);
    }
    return new RegularImmutableMap<K, V>(entries, table, mask);
  }

  private RegularImmutableMap(Entry<K, V>[] entries, ImmutableMapEntry[] table, int mask) {
    this.entries = entries;
    this.table = table;
    this.mask = mask;
  }

  static void checkNoConflictInKeyBucket(
      Object key, Entry<?, ?> entry, @Nullable ImmutableMapEntry keyBucketHead) {
    for (; keyBucketHead != null; keyBucketHead = keyBucketHead.getNextInKeyBucket()) {
      checkNoConflict(!key.equals(keyBucketHead.getKey()), "key", entry, keyBucketHead);
    }
  }

  /**
   * 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;

  @Override
  public V get(@Nullable Object key) {
    return get(key, table, mask);
  }

  @Nullable
  static <V> V get(@Nullable Object key, ImmutableMapEntry[] keyTable, int mask) {
    if (key == null) {
      return null;
    }
    int index = Hashing.smear(key.hashCode()) & mask;
    for (ImmutableMapEntry<?, V> entry = keyTable[index];
        entry != null;
        entry = entry.getNextInKeyBucket()) {
      Object 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 createEntrySet() {
    return new ImmutableMapEntrySet.RegularEntrySet<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;
}