/*
* 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.checkArgument;
import com.google.common.annotations.GwtCompatible;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;
/**
* 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 LinkedEntry<K, V>[] entries;
// array of linked lists of entries
private final transient LinkedEntry<K, V>[] table;
// 'and' with an int to get a table index
private final transient int mask;
private final transient int keySetHashCode;
// TODO(gak): investigate avoiding the creation of ImmutableEntries since we
// re-copy them anyway.
RegularImmutableMap(Entry<?, ?>... immutableEntries) {
int size = immutableEntries.length;
entries = createEntryArray(size);
int tableSize = chooseTableSize(size);
table = createEntryArray(tableSize);
mask = tableSize - 1;
int keySetHashCodeMutable = 0;
for (int entryIndex = 0; entryIndex < size; entryIndex++) {
// each of our 6 callers carefully put only Entry<K, V>s into the array!
@SuppressWarnings("unchecked")
Entry<K, V> entry = (Entry<K, V>) immutableEntries[entryIndex];
K key = entry.getKey();
int keyHashCode = key.hashCode();
keySetHashCodeMutable += keyHashCode;
int tableIndex = Hashing.smear(keyHashCode) & mask;
@Nullable LinkedEntry<K, V> existing = table[tableIndex];
// prepend, not append, so the entries can be immutable
LinkedEntry<K, V> linkedEntry =
newLinkedEntry(key, entry.getValue(), existing);
table[tableIndex] = linkedEntry;
entries[entryIndex] = linkedEntry;
while (existing != null) {
checkArgument(!key.equals(existing.getKey()), "duplicate key: %s", key);
existing = existing.next();
}
}
keySetHashCode = keySetHashCodeMutable;
}
/**
* 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;
/**
* Give a good hash table size for the given number of keys.
*
* @param size The number of keys to be inserted. Must be greater than or equal to 2.
*/
private static int chooseTableSize(int size) {
// Get the recommended table size.
// Round down to the nearest power of 2.
int tableSize = Integer.highestOneBit(size);
// Check to make sure that we will not exceed the maximum load factor.
if ((double) size / tableSize > MAX_LOAD_FACTOR) {
tableSize <<= 1;
checkArgument(tableSize > 0, "table too large: %s", size);
}
return tableSize;
}
/**
* Creates a {@link LinkedEntry} array to hold parameterized entries. The
* result must never be upcast back to LinkedEntry[] (or Object[], etc.), or
* allowed to escape the class.
*/
@SuppressWarnings("unchecked") // Safe as long as the javadocs are followed
private LinkedEntry<K, V>[] createEntryArray(int size) {
return new LinkedEntry[size];
}
private static <K, V> LinkedEntry<K, V> newLinkedEntry(K key, V value,
@Nullable LinkedEntry<K, V> next) {
return (next == null)
? new TerminalEntry<K, V>(key, value)
: new NonTerminalEntry<K, V>(key, value, next);
}
private interface LinkedEntry<K, V> extends Entry<K, V> {
/** Returns the next entry in the list or {@code null} if none exists. */
@Nullable LinkedEntry<K, V> next();
}
/** {@code LinkedEntry} implementation that has a next value. */
@Immutable
@SuppressWarnings("serial") // this class is never serialized
private static final class NonTerminalEntry<K, V>
extends ImmutableEntry<K, V> implements LinkedEntry<K, V> {
final LinkedEntry<K, V> next;
NonTerminalEntry(K key, V value, LinkedEntry<K, V> next) {
super(key, value);
this.next = next;
}
@Override public LinkedEntry<K, V> next() {
return next;
}
}
/**
* {@code LinkedEntry} implementation that serves as the last entry in the
* list. I.e. no next entry
*/
@Immutable
@SuppressWarnings("serial") // this class is never serialized
private static final class TerminalEntry<K, V> extends ImmutableEntry<K, V>
implements LinkedEntry<K, V> {
TerminalEntry(K key, V value) {
super(key, value);
}
@Nullable @Override public LinkedEntry<K, V> next() {
return null;
}
}
@Override public V get(@Nullable Object key) {
if (key == null) {
return null;
}
int index = Hashing.smear(key.hashCode()) & mask;
for (LinkedEntry<K, V> entry = table[index];
entry != null;
entry = entry.next()) {
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 public boolean isEmpty() {
return false;
}
@Override public boolean containsValue(@Nullable Object value) {
if (value == null) {
return false;
}
for (Entry<K, V> entry : entries) {
if (entry.getValue().equals(value)) {
return true;
}
}
return false;
}
@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);
}
}
@Override
ImmutableSet<K> createKeySet() {
return new ImmutableMapKeySet<K, V>(entrySet(), keySetHashCode) {
@Override ImmutableMap<K, V> map() {
return RegularImmutableMap.this;
}
};
}
@Override public String toString() {
StringBuilder result
= Collections2.newStringBuilderForCollection(size()).append('{');
Collections2.STANDARD_JOINER.appendTo(result, entries);
return result.append('}').toString();
}
// 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;
}