1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/emul/compact/src/main/java/java/util/LinkedHashMap.java Wed Jan 23 22:32:27 2013 +0100
1.3 @@ -0,0 +1,491 @@
1.4 +/*
1.5 + * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation. Oracle designates this
1.11 + * particular file as subject to the "Classpath" exception as provided
1.12 + * by Oracle in the LICENSE file that accompanied this code.
1.13 + *
1.14 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 + * version 2 for more details (a copy is included in the LICENSE file that
1.18 + * accompanied this code).
1.19 + *
1.20 + * You should have received a copy of the GNU General Public License version
1.21 + * 2 along with this work; if not, write to the Free Software Foundation,
1.22 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 + *
1.24 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 + * or visit www.oracle.com if you need additional information or have any
1.26 + * questions.
1.27 + */
1.28 +
1.29 +package java.util;
1.30 +import java.io.*;
1.31 +
1.32 +/**
1.33 + * <p>Hash table and linked list implementation of the <tt>Map</tt> interface,
1.34 + * with predictable iteration order. This implementation differs from
1.35 + * <tt>HashMap</tt> in that it maintains a doubly-linked list running through
1.36 + * all of its entries. This linked list defines the iteration ordering,
1.37 + * which is normally the order in which keys were inserted into the map
1.38 + * (<i>insertion-order</i>). Note that insertion order is not affected
1.39 + * if a key is <i>re-inserted</i> into the map. (A key <tt>k</tt> is
1.40 + * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when
1.41 + * <tt>m.containsKey(k)</tt> would return <tt>true</tt> immediately prior to
1.42 + * the invocation.)
1.43 + *
1.44 + * <p>This implementation spares its clients from the unspecified, generally
1.45 + * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}),
1.46 + * without incurring the increased cost associated with {@link TreeMap}. It
1.47 + * can be used to produce a copy of a map that has the same order as the
1.48 + * original, regardless of the original map's implementation:
1.49 + * <pre>
1.50 + * void foo(Map m) {
1.51 + * Map copy = new LinkedHashMap(m);
1.52 + * ...
1.53 + * }
1.54 + * </pre>
1.55 + * This technique is particularly useful if a module takes a map on input,
1.56 + * copies it, and later returns results whose order is determined by that of
1.57 + * the copy. (Clients generally appreciate having things returned in the same
1.58 + * order they were presented.)
1.59 + *
1.60 + * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is
1.61 + * provided to create a linked hash map whose order of iteration is the order
1.62 + * in which its entries were last accessed, from least-recently accessed to
1.63 + * most-recently (<i>access-order</i>). This kind of map is well-suited to
1.64 + * building LRU caches. Invoking the <tt>put</tt> or <tt>get</tt> method
1.65 + * results in an access to the corresponding entry (assuming it exists after
1.66 + * the invocation completes). The <tt>putAll</tt> method generates one entry
1.67 + * access for each mapping in the specified map, in the order that key-value
1.68 + * mappings are provided by the specified map's entry set iterator. <i>No
1.69 + * other methods generate entry accesses.</i> In particular, operations on
1.70 + * collection-views do <i>not</i> affect the order of iteration of the backing
1.71 + * map.
1.72 + *
1.73 + * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to
1.74 + * impose a policy for removing stale mappings automatically when new mappings
1.75 + * are added to the map.
1.76 + *
1.77 + * <p>This class provides all of the optional <tt>Map</tt> operations, and
1.78 + * permits null elements. Like <tt>HashMap</tt>, it provides constant-time
1.79 + * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and
1.80 + * <tt>remove</tt>), assuming the hash function disperses elements
1.81 + * properly among the buckets. Performance is likely to be just slightly
1.82 + * below that of <tt>HashMap</tt>, due to the added expense of maintaining the
1.83 + * linked list, with one exception: Iteration over the collection-views
1.84 + * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i>
1.85 + * of the map, regardless of its capacity. Iteration over a <tt>HashMap</tt>
1.86 + * is likely to be more expensive, requiring time proportional to its
1.87 + * <i>capacity</i>.
1.88 + *
1.89 + * <p>A linked hash map has two parameters that affect its performance:
1.90 + * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely
1.91 + * as for <tt>HashMap</tt>. Note, however, that the penalty for choosing an
1.92 + * excessively high value for initial capacity is less severe for this class
1.93 + * than for <tt>HashMap</tt>, as iteration times for this class are unaffected
1.94 + * by capacity.
1.95 + *
1.96 + * <p><strong>Note that this implementation is not synchronized.</strong>
1.97 + * If multiple threads access a linked hash map concurrently, and at least
1.98 + * one of the threads modifies the map structurally, it <em>must</em> be
1.99 + * synchronized externally. This is typically accomplished by
1.100 + * synchronizing on some object that naturally encapsulates the map.
1.101 + *
1.102 + * If no such object exists, the map should be "wrapped" using the
1.103 + * {@link Collections#synchronizedMap Collections.synchronizedMap}
1.104 + * method. This is best done at creation time, to prevent accidental
1.105 + * unsynchronized access to the map:<pre>
1.106 + * Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre>
1.107 + *
1.108 + * A structural modification is any operation that adds or deletes one or more
1.109 + * mappings or, in the case of access-ordered linked hash maps, affects
1.110 + * iteration order. In insertion-ordered linked hash maps, merely changing
1.111 + * the value associated with a key that is already contained in the map is not
1.112 + * a structural modification. <strong>In access-ordered linked hash maps,
1.113 + * merely querying the map with <tt>get</tt> is a structural
1.114 + * modification.</strong>)
1.115 + *
1.116 + * <p>The iterators returned by the <tt>iterator</tt> method of the collections
1.117 + * returned by all of this class's collection view methods are
1.118 + * <em>fail-fast</em>: if the map is structurally modified at any time after
1.119 + * the iterator is created, in any way except through the iterator's own
1.120 + * <tt>remove</tt> method, the iterator will throw a {@link
1.121 + * ConcurrentModificationException}. Thus, in the face of concurrent
1.122 + * modification, the iterator fails quickly and cleanly, rather than risking
1.123 + * arbitrary, non-deterministic behavior at an undetermined time in the future.
1.124 + *
1.125 + * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
1.126 + * as it is, generally speaking, impossible to make any hard guarantees in the
1.127 + * presence of unsynchronized concurrent modification. Fail-fast iterators
1.128 + * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
1.129 + * Therefore, it would be wrong to write a program that depended on this
1.130 + * exception for its correctness: <i>the fail-fast behavior of iterators
1.131 + * should be used only to detect bugs.</i>
1.132 + *
1.133 + * <p>This class is a member of the
1.134 + * <a href="{@docRoot}/../technotes/guides/collections/index.html">
1.135 + * Java Collections Framework</a>.
1.136 + *
1.137 + * @param <K> the type of keys maintained by this map
1.138 + * @param <V> the type of mapped values
1.139 + *
1.140 + * @author Josh Bloch
1.141 + * @see Object#hashCode()
1.142 + * @see Collection
1.143 + * @see Map
1.144 + * @see HashMap
1.145 + * @see TreeMap
1.146 + * @see Hashtable
1.147 + * @since 1.4
1.148 + */
1.149 +
1.150 +public class LinkedHashMap<K,V>
1.151 + extends HashMap<K,V>
1.152 + implements Map<K,V>
1.153 +{
1.154 +
1.155 + private static final long serialVersionUID = 3801124242820219131L;
1.156 +
1.157 + /**
1.158 + * The head of the doubly linked list.
1.159 + */
1.160 + private transient Entry<K,V> header;
1.161 +
1.162 + /**
1.163 + * The iteration ordering method for this linked hash map: <tt>true</tt>
1.164 + * for access-order, <tt>false</tt> for insertion-order.
1.165 + *
1.166 + * @serial
1.167 + */
1.168 + private final boolean accessOrder;
1.169 +
1.170 + /**
1.171 + * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
1.172 + * with the specified initial capacity and load factor.
1.173 + *
1.174 + * @param initialCapacity the initial capacity
1.175 + * @param loadFactor the load factor
1.176 + * @throws IllegalArgumentException if the initial capacity is negative
1.177 + * or the load factor is nonpositive
1.178 + */
1.179 + public LinkedHashMap(int initialCapacity, float loadFactor) {
1.180 + super(initialCapacity, loadFactor);
1.181 + accessOrder = false;
1.182 + }
1.183 +
1.184 + /**
1.185 + * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
1.186 + * with the specified initial capacity and a default load factor (0.75).
1.187 + *
1.188 + * @param initialCapacity the initial capacity
1.189 + * @throws IllegalArgumentException if the initial capacity is negative
1.190 + */
1.191 + public LinkedHashMap(int initialCapacity) {
1.192 + super(initialCapacity);
1.193 + accessOrder = false;
1.194 + }
1.195 +
1.196 + /**
1.197 + * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
1.198 + * with the default initial capacity (16) and load factor (0.75).
1.199 + */
1.200 + public LinkedHashMap() {
1.201 + super();
1.202 + accessOrder = false;
1.203 + }
1.204 +
1.205 + /**
1.206 + * Constructs an insertion-ordered <tt>LinkedHashMap</tt> instance with
1.207 + * the same mappings as the specified map. The <tt>LinkedHashMap</tt>
1.208 + * instance is created with a default load factor (0.75) and an initial
1.209 + * capacity sufficient to hold the mappings in the specified map.
1.210 + *
1.211 + * @param m the map whose mappings are to be placed in this map
1.212 + * @throws NullPointerException if the specified map is null
1.213 + */
1.214 + public LinkedHashMap(Map<? extends K, ? extends V> m) {
1.215 + super(m);
1.216 + accessOrder = false;
1.217 + }
1.218 +
1.219 + /**
1.220 + * Constructs an empty <tt>LinkedHashMap</tt> instance with the
1.221 + * specified initial capacity, load factor and ordering mode.
1.222 + *
1.223 + * @param initialCapacity the initial capacity
1.224 + * @param loadFactor the load factor
1.225 + * @param accessOrder the ordering mode - <tt>true</tt> for
1.226 + * access-order, <tt>false</tt> for insertion-order
1.227 + * @throws IllegalArgumentException if the initial capacity is negative
1.228 + * or the load factor is nonpositive
1.229 + */
1.230 + public LinkedHashMap(int initialCapacity,
1.231 + float loadFactor,
1.232 + boolean accessOrder) {
1.233 + super(initialCapacity, loadFactor);
1.234 + this.accessOrder = accessOrder;
1.235 + }
1.236 +
1.237 + /**
1.238 + * Called by superclass constructors and pseudoconstructors (clone,
1.239 + * readObject) before any entries are inserted into the map. Initializes
1.240 + * the chain.
1.241 + */
1.242 + void init() {
1.243 + header = new Entry<>(-1, null, null, null);
1.244 + header.before = header.after = header;
1.245 + }
1.246 +
1.247 + /**
1.248 + * Transfers all entries to new table array. This method is called
1.249 + * by superclass resize. It is overridden for performance, as it is
1.250 + * faster to iterate using our linked list.
1.251 + */
1.252 + void transfer(HashMap.Entry[] newTable) {
1.253 + int newCapacity = newTable.length;
1.254 + for (Entry<K,V> e = header.after; e != header; e = e.after) {
1.255 + int index = indexFor(e.hash, newCapacity);
1.256 + e.next = newTable[index];
1.257 + newTable[index] = e;
1.258 + }
1.259 + }
1.260 +
1.261 +
1.262 + /**
1.263 + * Returns <tt>true</tt> if this map maps one or more keys to the
1.264 + * specified value.
1.265 + *
1.266 + * @param value value whose presence in this map is to be tested
1.267 + * @return <tt>true</tt> if this map maps one or more keys to the
1.268 + * specified value
1.269 + */
1.270 + public boolean containsValue(Object value) {
1.271 + // Overridden to take advantage of faster iterator
1.272 + if (value==null) {
1.273 + for (Entry e = header.after; e != header; e = e.after)
1.274 + if (e.value==null)
1.275 + return true;
1.276 + } else {
1.277 + for (Entry e = header.after; e != header; e = e.after)
1.278 + if (value.equals(e.value))
1.279 + return true;
1.280 + }
1.281 + return false;
1.282 + }
1.283 +
1.284 + /**
1.285 + * Returns the value to which the specified key is mapped,
1.286 + * or {@code null} if this map contains no mapping for the key.
1.287 + *
1.288 + * <p>More formally, if this map contains a mapping from a key
1.289 + * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
1.290 + * key.equals(k))}, then this method returns {@code v}; otherwise
1.291 + * it returns {@code null}. (There can be at most one such mapping.)
1.292 + *
1.293 + * <p>A return value of {@code null} does not <i>necessarily</i>
1.294 + * indicate that the map contains no mapping for the key; it's also
1.295 + * possible that the map explicitly maps the key to {@code null}.
1.296 + * The {@link #containsKey containsKey} operation may be used to
1.297 + * distinguish these two cases.
1.298 + */
1.299 + public V get(Object key) {
1.300 + Entry<K,V> e = (Entry<K,V>)getEntry(key);
1.301 + if (e == null)
1.302 + return null;
1.303 + e.recordAccess(this);
1.304 + return e.value;
1.305 + }
1.306 +
1.307 + /**
1.308 + * Removes all of the mappings from this map.
1.309 + * The map will be empty after this call returns.
1.310 + */
1.311 + public void clear() {
1.312 + super.clear();
1.313 + header.before = header.after = header;
1.314 + }
1.315 +
1.316 + /**
1.317 + * LinkedHashMap entry.
1.318 + */
1.319 + private static class Entry<K,V> extends HashMap.Entry<K,V> {
1.320 + // These fields comprise the doubly linked list used for iteration.
1.321 + Entry<K,V> before, after;
1.322 +
1.323 + Entry(int hash, K key, V value, HashMap.Entry<K,V> next) {
1.324 + super(hash, key, value, next);
1.325 + }
1.326 +
1.327 + /**
1.328 + * Removes this entry from the linked list.
1.329 + */
1.330 + private void remove() {
1.331 + before.after = after;
1.332 + after.before = before;
1.333 + }
1.334 +
1.335 + /**
1.336 + * Inserts this entry before the specified existing entry in the list.
1.337 + */
1.338 + private void addBefore(Entry<K,V> existingEntry) {
1.339 + after = existingEntry;
1.340 + before = existingEntry.before;
1.341 + before.after = this;
1.342 + after.before = this;
1.343 + }
1.344 +
1.345 + /**
1.346 + * This method is invoked by the superclass whenever the value
1.347 + * of a pre-existing entry is read by Map.get or modified by Map.set.
1.348 + * If the enclosing Map is access-ordered, it moves the entry
1.349 + * to the end of the list; otherwise, it does nothing.
1.350 + */
1.351 + void recordAccess(HashMap<K,V> m) {
1.352 + LinkedHashMap<K,V> lm = (LinkedHashMap<K,V>)m;
1.353 + if (lm.accessOrder) {
1.354 + lm.modCount++;
1.355 + remove();
1.356 + addBefore(lm.header);
1.357 + }
1.358 + }
1.359 +
1.360 + void recordRemoval(HashMap<K,V> m) {
1.361 + remove();
1.362 + }
1.363 + }
1.364 +
1.365 + private abstract class LinkedHashIterator<T> implements Iterator<T> {
1.366 + Entry<K,V> nextEntry = header.after;
1.367 + Entry<K,V> lastReturned = null;
1.368 +
1.369 + /**
1.370 + * The modCount value that the iterator believes that the backing
1.371 + * List should have. If this expectation is violated, the iterator
1.372 + * has detected concurrent modification.
1.373 + */
1.374 + int expectedModCount = modCount;
1.375 +
1.376 + public boolean hasNext() {
1.377 + return nextEntry != header;
1.378 + }
1.379 +
1.380 + public void remove() {
1.381 + if (lastReturned == null)
1.382 + throw new IllegalStateException();
1.383 + if (modCount != expectedModCount)
1.384 + throw new ConcurrentModificationException();
1.385 +
1.386 + LinkedHashMap.this.remove(lastReturned.key);
1.387 + lastReturned = null;
1.388 + expectedModCount = modCount;
1.389 + }
1.390 +
1.391 + Entry<K,V> nextEntry() {
1.392 + if (modCount != expectedModCount)
1.393 + throw new ConcurrentModificationException();
1.394 + if (nextEntry == header)
1.395 + throw new NoSuchElementException();
1.396 +
1.397 + Entry<K,V> e = lastReturned = nextEntry;
1.398 + nextEntry = e.after;
1.399 + return e;
1.400 + }
1.401 + }
1.402 +
1.403 + private class KeyIterator extends LinkedHashIterator<K> {
1.404 + public K next() { return nextEntry().getKey(); }
1.405 + }
1.406 +
1.407 + private class ValueIterator extends LinkedHashIterator<V> {
1.408 + public V next() { return nextEntry().value; }
1.409 + }
1.410 +
1.411 + private class EntryIterator extends LinkedHashIterator<Map.Entry<K,V>> {
1.412 + public Map.Entry<K,V> next() { return nextEntry(); }
1.413 + }
1.414 +
1.415 + // These Overrides alter the behavior of superclass view iterator() methods
1.416 + Iterator<K> newKeyIterator() { return new KeyIterator(); }
1.417 + Iterator<V> newValueIterator() { return new ValueIterator(); }
1.418 + Iterator<Map.Entry<K,V>> newEntryIterator() { return new EntryIterator(); }
1.419 +
1.420 + /**
1.421 + * This override alters behavior of superclass put method. It causes newly
1.422 + * allocated entry to get inserted at the end of the linked list and
1.423 + * removes the eldest entry if appropriate.
1.424 + */
1.425 + void addEntry(int hash, K key, V value, int bucketIndex) {
1.426 + createEntry(hash, key, value, bucketIndex);
1.427 +
1.428 + // Remove eldest entry if instructed, else grow capacity if appropriate
1.429 + Entry<K,V> eldest = header.after;
1.430 + if (removeEldestEntry(eldest)) {
1.431 + removeEntryForKey(eldest.key);
1.432 + } else {
1.433 + if (size >= threshold)
1.434 + resize(2 * table.length);
1.435 + }
1.436 + }
1.437 +
1.438 + /**
1.439 + * This override differs from addEntry in that it doesn't resize the
1.440 + * table or remove the eldest entry.
1.441 + */
1.442 + void createEntry(int hash, K key, V value, int bucketIndex) {
1.443 + HashMap.Entry<K,V> old = table[bucketIndex];
1.444 + Entry<K,V> e = new Entry<>(hash, key, value, old);
1.445 + table[bucketIndex] = e;
1.446 + e.addBefore(header);
1.447 + size++;
1.448 + }
1.449 +
1.450 + /**
1.451 + * Returns <tt>true</tt> if this map should remove its eldest entry.
1.452 + * This method is invoked by <tt>put</tt> and <tt>putAll</tt> after
1.453 + * inserting a new entry into the map. It provides the implementor
1.454 + * with the opportunity to remove the eldest entry each time a new one
1.455 + * is added. This is useful if the map represents a cache: it allows
1.456 + * the map to reduce memory consumption by deleting stale entries.
1.457 + *
1.458 + * <p>Sample use: this override will allow the map to grow up to 100
1.459 + * entries and then delete the eldest entry each time a new entry is
1.460 + * added, maintaining a steady state of 100 entries.
1.461 + * <pre>
1.462 + * private static final int MAX_ENTRIES = 100;
1.463 + *
1.464 + * protected boolean removeEldestEntry(Map.Entry eldest) {
1.465 + * return size() > MAX_ENTRIES;
1.466 + * }
1.467 + * </pre>
1.468 + *
1.469 + * <p>This method typically does not modify the map in any way,
1.470 + * instead allowing the map to modify itself as directed by its
1.471 + * return value. It <i>is</i> permitted for this method to modify
1.472 + * the map directly, but if it does so, it <i>must</i> return
1.473 + * <tt>false</tt> (indicating that the map should not attempt any
1.474 + * further modification). The effects of returning <tt>true</tt>
1.475 + * after modifying the map from within this method are unspecified.
1.476 + *
1.477 + * <p>This implementation merely returns <tt>false</tt> (so that this
1.478 + * map acts like a normal map - the eldest element is never removed).
1.479 + *
1.480 + * @param eldest The least recently inserted entry in the map, or if
1.481 + * this is an access-ordered map, the least recently accessed
1.482 + * entry. This is the entry that will be removed it this
1.483 + * method returns <tt>true</tt>. If the map was empty prior
1.484 + * to the <tt>put</tt> or <tt>putAll</tt> invocation resulting
1.485 + * in this invocation, this will be the entry that was just
1.486 + * inserted; in other words, if the map contains a single
1.487 + * entry, the eldest entry is also the newest.
1.488 + * @return <tt>true</tt> if the eldest entry should be removed
1.489 + * from the map; <tt>false</tt> if it should be retained.
1.490 + */
1.491 + protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
1.492 + return false;
1.493 + }
1.494 +}