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My first initial commit with all of mine experimental changes.

Dmitry Kabak (userdima committed 13 years ago

Commit d37b88d1 parent 3f5b46618352 files · +2598093 −-8690Browse files

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1+/*
2+ * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
3+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4+ *
5+ * This code is free software; you can redistribute it and/or modify it
6+ * under the terms of the GNU General Public License version 2 only, as
7+ * published by the Free Software Foundation. Oracle designates this
8+ * particular file as subject to the "Classpath" exception as provided
9+ * by Oracle in the LICENSE file that accompanied this code.
10+ *
11+ * This code is distributed in the hope that it will be useful, but WITHOUT
12+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14+ * version 2 for more details (a copy is included in the LICENSE file that
15+ * accompanied this code).
16+ *
17+ * You should have received a copy of the GNU General Public License version
18+ * 2 along with this work; if not, write to the Free Software Foundation,
19+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20+ *
21+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22+ * or visit www.oracle.com if you need additional information or have any
23+ * questions.
24+ */
25+
26+package java.util;
27+import java.io.*;
28+
29+/**
30+ * <p>Hash table and linked list implementation of the <tt>Map</tt> interface,
31+ * with predictable iteration order. This implementation differs from
32+ * <tt>HashMap</tt> in that it maintains a doubly-linked list running through
33+ * all of its entries. This linked list defines the iteration ordering,
34+ * which is normally the order in which keys were inserted into the map
35+ * (<i>insertion-order</i>). Note that insertion order is not affected
36+ * if a key is <i>re-inserted</i> into the map. (A key <tt>k</tt> is
37+ * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when
38+ * <tt>m.containsKey(k)</tt> would return <tt>true</tt> immediately prior to
39+ * the invocation.)
40+ *
41+ * <p>This implementation spares its clients from the unspecified, generally
42+ * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}),
43+ * without incurring the increased cost associated with {@link TreeMap}. It
44+ * can be used to produce a copy of a map that has the same order as the
45+ * original, regardless of the original map's implementation:
46+ * <pre>
47+ * void foo(Map m) {
48+ * Map copy = new LinkedHashMap(m);
49+ * ...
50+ * }
51+ * </pre>
52+ * This technique is particularly useful if a module takes a map on input,
53+ * copies it, and later returns results whose order is determined by that of
54+ * the copy. (Clients generally appreciate having things returned in the same
55+ * order they were presented.)
56+ *
57+ * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is
58+ * provided to create a linked hash map whose order of iteration is the order
59+ * in which its entries were last accessed, from least-recently accessed to
60+ * most-recently (<i>access-order</i>). This kind of map is well-suited to
61+ * building LRU caches. Invoking the <tt>put</tt> or <tt>get</tt> method
62+ * results in an access to the corresponding entry (assuming it exists after
63+ * the invocation completes). The <tt>putAll</tt> method generates one entry
64+ * access for each mapping in the specified map, in the order that key-value
65+ * mappings are provided by the specified map's entry set iterator. <i>No
66+ * other methods generate entry accesses.</i> In particular, operations on
67+ * collection-views do <i>not</i> affect the order of iteration of the backing
68+ * map.
69+ *
70+ * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to
71+ * impose a policy for removing stale mappings automatically when new mappings
72+ * are added to the map.
73+ *
74+ * <p>This class provides all of the optional <tt>Map</tt> operations, and
75+ * permits null elements. Like <tt>HashMap</tt>, it provides constant-time
76+ * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and
77+ * <tt>remove</tt>), assuming the hash function disperses elements
78+ * properly among the buckets. Performance is likely to be just slightly
79+ * below that of <tt>HashMap</tt>, due to the added expense of maintaining the
80+ * linked list, with one exception: Iteration over the collection-views
81+ * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i>
82+ * of the map, regardless of its capacity. Iteration over a <tt>HashMap</tt>
83+ * is likely to be more expensive, requiring time proportional to its
84+ * <i>capacity</i>.
85+ *
86+ * <p>A linked hash map has two parameters that affect its performance:
87+ * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely
88+ * as for <tt>HashMap</tt>. Note, however, that the penalty for choosing an
89+ * excessively high value for initial capacity is less severe for this class
90+ * than for <tt>HashMap</tt>, as iteration times for this class are unaffected
91+ * by capacity.
92+ *
93+ * <p><strong>Note that this implementation is not synchronized.</strong>
94+ * If multiple threads access a linked hash map concurrently, and at least
95+ * one of the threads modifies the map structurally, it <em>must</em> be
96+ * synchronized externally. This is typically accomplished by
97+ * synchronizing on some object that naturally encapsulates the map.
98+ *
99+ * If no such object exists, the map should be "wrapped" using the
100+ * {@link Collections#synchronizedMap Collections.synchronizedMap}
101+ * method. This is best done at creation time, to prevent accidental
102+ * unsynchronized access to the map:<pre>
103+ * Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre>
104+ *
105+ * A structural modification is any operation that adds or deletes one or more
106+ * mappings or, in the case of access-ordered linked hash maps, affects
107+ * iteration order. In insertion-ordered linked hash maps, merely changing
108+ * the value associated with a key that is already contained in the map is not
109+ * a structural modification. <strong>In access-ordered linked hash maps,
110+ * merely querying the map with <tt>get</tt> is a structural
111+ * modification.</strong>)
112+ *
113+ * <p>The iterators returned by the <tt>iterator</tt> method of the collections
114+ * returned by all of this class's collection view methods are
115+ * <em>fail-fast</em>: if the map is structurally modified at any time after
116+ * the iterator is created, in any way except through the iterator's own
117+ * <tt>remove</tt> method, the iterator will throw a {@link
118+ * ConcurrentModificationException}. Thus, in the face of concurrent
119+ * modification, the iterator fails quickly and cleanly, rather than risking
120+ * arbitrary, non-deterministic behavior at an undetermined time in the future.
121+ *
122+ * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
123+ * as it is, generally speaking, impossible to make any hard guarantees in the
124+ * presence of unsynchronized concurrent modification. Fail-fast iterators
125+ * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
126+ * Therefore, it would be wrong to write a program that depended on this
127+ * exception for its correctness: <i>the fail-fast behavior of iterators
128+ * should be used only to detect bugs.</i>
129+ *
130+ * <p>This class is a member of the
131+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
132+ * Java Collections Framework</a>.
133+ *
134+ * @param <K> the type of keys maintained by this map
135+ * @param <V> the type of mapped values
136+ *
137+ * @author Josh Bloch
138+ * @see Object#hashCode()
139+ * @see Collection
140+ * @see Map
141+ * @see HashMap
142+ * @see TreeMap
143+ * @see Hashtable
144+ * @since 1.4
145+ */
146+
147+public class LinkedHashMap<K,V>
148+ extends HashMap<K,V>
149+ implements Map<K,V>
150+{
151+
152+ private static final long serialVersionUID = 3801124242820219131L;
153+
154+ /**
155+ * The head of the doubly linked list.
156+ */
157+ private transient Entry<K,V> header;
158+
159+ /**
160+ * The iteration ordering method for this linked hash map: <tt>true</tt>
161+ * for access-order, <tt>false</tt> for insertion-order.
162+ *
163+ * @serial
164+ */
165+ private final boolean accessOrder;
166+
167+ /**
168+ * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
169+ * with the specified initial capacity and load factor.
170+ *
171+ * @param initialCapacity the initial capacity
172+ * @param loadFactor the load factor
173+ * @throws IllegalArgumentException if the initial capacity is negative
174+ * or the load factor is nonpositive
175+ */
176+ public LinkedHashMap(int initialCapacity, float loadFactor) {
177+ super(initialCapacity, loadFactor);
178+ accessOrder = false;
179+ }
180+
181+ /**
182+ * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
183+ * with the specified initial capacity and a default load factor (0.75).
184+ *
185+ * @param initialCapacity the initial capacity
186+ * @throws IllegalArgumentException if the initial capacity is negative
187+ */
188+ public LinkedHashMap(int initialCapacity) {
189+ super(initialCapacity);
190+ accessOrder = false;
191+ }
192+
193+ /**
194+ * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
195+ * with the default initial capacity (16) and load factor (0.75).
196+ */
197+ public LinkedHashMap() {
198+ super();
199+ accessOrder = false;
200+ }
201+
202+ /**
203+ * Constructs an insertion-ordered <tt>LinkedHashMap</tt> instance with
204+ * the same mappings as the specified map. The <tt>LinkedHashMap</tt>
205+ * instance is created with a default load factor (0.75) and an initial
206+ * capacity sufficient to hold the mappings in the specified map.
207+ *
208+ * @param m the map whose mappings are to be placed in this map
209+ * @throws NullPointerException if the specified map is null
210+ */
211+ public LinkedHashMap(Map<? extends K, ? extends V> m) {
212+ super(m);
213+ accessOrder = false;
214+ }
215+
216+ /**
217+ * Constructs an empty <tt>LinkedHashMap</tt> instance with the
218+ * specified initial capacity, load factor and ordering mode.
219+ *
220+ * @param initialCapacity the initial capacity
221+ * @param loadFactor the load factor
222+ * @param accessOrder the ordering mode - <tt>true</tt> for
223+ * access-order, <tt>false</tt> for insertion-order
224+ * @throws IllegalArgumentException if the initial capacity is negative
225+ * or the load factor is nonpositive
226+ */
227+ public LinkedHashMap(int initialCapacity,
228+ float loadFactor,
229+ boolean accessOrder) {
230+ super(initialCapacity, loadFactor);
231+ this.accessOrder = accessOrder;
232+ }
233+
234+ /**
235+ * Called by superclass constructors and pseudoconstructors (clone,
236+ * readObject) before any entries are inserted into the map. Initializes
237+ * the chain.
238+ */
239+ void init() {
240+ header = new Entry<>(-1, null, null, null);
241+ header.before = header.after = header;
242+ }
243+
244+ /**
245+ * Transfers all entries to new table array. This method is called
246+ * by superclass resize. It is overridden for performance, as it is
247+ * faster to iterate using our linked list.
248+ */
249+ void transfer(HashMap.Entry[] newTable) {
250+ int newCapacity = newTable.length;
251+ for (Entry<K,V> e = header.after; e != header; e = e.after) {
252+ int index = indexFor(e.hash, newCapacity);
253+ e.next = newTable[index];
254+ newTable[index] = e;
255+ }
256+ }
257+
258+
259+ /**
260+ * Returns <tt>true</tt> if this map maps one or more keys to the
261+ * specified value.
262+ *
263+ * @param value value whose presence in this map is to be tested
264+ * @return <tt>true</tt> if this map maps one or more keys to the
265+ * specified value
266+ */
267+ public boolean containsValue(Object value) {
268+ // Overridden to take advantage of faster iterator
269+ if (value==null) {
270+ for (Entry e = header.after; e != header; e = e.after)
271+ if (e.value==null)
272+ return true;
273+ } else {
274+ for (Entry e = header.after; e != header; e = e.after)
275+ if (value.equals(e.value))
276+ return true;
277+ }
278+ return false;
279+ }
280+
281+ /**
282+ * Returns the value to which the specified key is mapped,
283+ * or {@code null} if this map contains no mapping for the key.
284+ *
285+ * <p>More formally, if this map contains a mapping from a key
286+ * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
287+ * key.equals(k))}, then this method returns {@code v}; otherwise
288+ * it returns {@code null}. (There can be at most one such mapping.)
289+ *
290+ * <p>A return value of {@code null} does not <i>necessarily</i>
291+ * indicate that the map contains no mapping for the key; it's also
292+ * possible that the map explicitly maps the key to {@code null}.
293+ * The {@link #containsKey containsKey} operation may be used to
294+ * distinguish these two cases.
295+ */
296+ public V get(Object key) {
297+ Entry<K,V> e = (Entry<K,V>)getEntry(key);
298+ if (e == null)
299+ return null;
300+ e.recordAccess(this);
301+ return e.value;
302+ }
303+
304+ /**
305+ * Removes all of the mappings from this map.
306+ * The map will be empty after this call returns.
307+ */
308+ public void clear() {
309+ super.clear();
310+ header.before = header.after = header;
311+ }
312+
313+ /**
314+ * LinkedHashMap entry.
315+ */
316+ private static class Entry<K,V> extends HashMap.Entry<K,V> {
317+ // These fields comprise the doubly linked list used for iteration.
318+ Entry<K,V> before, after;
319+
320+ Entry(int hash, K key, V value, HashMap.Entry<K,V> next) {
321+ super(hash, key, value, next);
322+ }
323+
324+ /**
325+ * Removes this entry from the linked list.
326+ */
327+ private void remove() {
328+ before.after = after;
329+ after.before = before;
330+ }
331+
332+ /**
333+ * Inserts this entry before the specified existing entry in the list.
334+ */
335+ private void addBefore(Entry<K,V> existingEntry) {
336+ after = existingEntry;
337+ before = existingEntry.before;
338+ before.after = this;
339+ after.before = this;
340+ }
341+
342+ /**
343+ * This method is invoked by the superclass whenever the value
344+ * of a pre-existing entry is read by Map.get or modified by Map.set.
345+ * If the enclosing Map is access-ordered, it moves the entry
346+ * to the end of the list; otherwise, it does nothing.
347+ */
348+ void recordAccess(HashMap<K,V> m) {
349+ LinkedHashMap<K,V> lm = (LinkedHashMap<K,V>)m;
350+ if (lm.accessOrder) {
351+ lm.modCount++;
352+ remove();
353+ addBefore(lm.header);
354+ }
355+ }
356+
357+ void recordRemoval(HashMap<K,V> m) {
358+ remove();
359+ }
360+ }
361+
362+ private abstract class LinkedHashIterator<T> implements Iterator<T> {
363+ Entry<K,V> nextEntry = header.after;
364+ Entry<K,V> lastReturned = null;
365+
366+ /**
367+ * The modCount value that the iterator believes that the backing
368+ * List should have. If this expectation is violated, the iterator
369+ * has detected concurrent modification.
370+ */
371+ int expectedModCount = modCount;
372+
373+ public boolean hasNext() {
374+ return nextEntry != header;
375+ }
376+
377+ public void remove() {
378+ if (lastReturned == null)
379+ throw new IllegalStateException();
380+ if (modCount != expectedModCount)
381+ throw new ConcurrentModificationException();
382+
383+ LinkedHashMap.this.remove(lastReturned.key);
384+ lastReturned = null;
385+ expectedModCount = modCount;
386+ }
387+
388+ Entry<K,V> nextEntry() {
389+ if (modCount != expectedModCount)
390+ throw new ConcurrentModificationException();
391+ if (nextEntry == header)
392+ throw new NoSuchElementException();
393+
394+ Entry<K,V> e = lastReturned = nextEntry;
395+ nextEntry = e.after;
396+ return e;
397+ }
398+ }
399+
400+ private class KeyIterator extends LinkedHashIterator<K> {
401+ public K next() { return nextEntry().getKey(); }
402+ }
403+
404+ private class ValueIterator extends LinkedHashIterator<V> {
405+ public V next() { return nextEntry().value; }
406+ }
407+
408+ private class EntryIterator extends LinkedHashIterator<Map.Entry<K,V>> {
409+ public Map.Entry<K,V> next() { return nextEntry(); }
410+ }
411+
412+ // These Overrides alter the behavior of superclass view iterator() methods
413+ Iterator<K> newKeyIterator() { return new KeyIterator(); }
414+ Iterator<V> newValueIterator() { return new ValueIterator(); }
415+ Iterator<Map.Entry<K,V>> newEntryIterator() { return new EntryIterator(); }
416+
417+ /**
418+ * This override alters behavior of superclass put method. It causes newly
419+ * allocated entry to get inserted at the end of the linked list and
420+ * removes the eldest entry if appropriate.
421+ */
422+ void addEntry(int hash, K key, V value, int bucketIndex) {
423+ createEntry(hash, key, value, bucketIndex);
424+
425+ // Remove eldest entry if instructed, else grow capacity if appropriate
426+ Entry<K,V> eldest = header.after;
427+ if (removeEldestEntry(eldest)) {
428+ removeEntryForKey(eldest.key);
429+ } else {
430+ if (size >= threshold)
431+ resize(2 * table.length);
432+ }
433+ }
434+
435+ /**
436+ * This override differs from addEntry in that it doesn't resize the
437+ * table or remove the eldest entry.
438+ */
439+ void createEntry(int hash, K key, V value, int bucketIndex) {
440+ HashMap.Entry<K,V> old = table[bucketIndex];
441+ Entry<K,V> e = new Entry<>(hash, key, value, old);
442+ table[bucketIndex] = e;
443+ e.addBefore(header);
444+ size++;
445+ }
446+
447+ /**
448+ * Returns <tt>true</tt> if this map should remove its eldest entry.
449+ * This method is invoked by <tt>put</tt> and <tt>putAll</tt> after
450+ * inserting a new entry into the map. It provides the implementor
451+ * with the opportunity to remove the eldest entry each time a new one
452+ * is added. This is useful if the map represents a cache: it allows
453+ * the map to reduce memory consumption by deleting stale entries.
454+ *
455+ * <p>Sample use: this override will allow the map to grow up to 100
456+ * entries and then delete the eldest entry each time a new entry is
457+ * added, maintaining a steady state of 100 entries.
458+ * <pre>
459+ * private static final int MAX_ENTRIES = 100;
460+ *
461+ * protected boolean removeEldestEntry(Map.Entry eldest) {
462+ * return size() > MAX_ENTRIES;
463+ * }
464+ * </pre>
465+ *
466+ * <p>This method typically does not modify the map in any way,
467+ * instead allowing the map to modify itself as directed by its
468+ * return value. It <i>is</i> permitted for this method to modify
469+ * the map directly, but if it does so, it <i>must</i> return
470+ * <tt>false</tt> (indicating that the map should not attempt any
471+ * further modification). The effects of returning <tt>true</tt>
472+ * after modifying the map from within this method are unspecified.
473+ *
474+ * <p>This implementation merely returns <tt>false</tt> (so that this
475+ * map acts like a normal map - the eldest element is never removed).
476+ *
477+ * @param eldest The least recently inserted entry in the map, or if
478+ * this is an access-ordered map, the least recently accessed
479+ * entry. This is the entry that will be removed it this
480+ * method returns <tt>true</tt>. If the map was empty prior
481+ * to the <tt>put</tt> or <tt>putAll</tt> invocation resulting
482+ * in this invocation, this will be the entry that was just
483+ * inserted; in other words, if the map contains a single
484+ * entry, the eldest entry is also the newest.
485+ * @return <tt>true</tt> if the eldest entry should be removed
486+ * from the map; <tt>false</tt> if it should be retained.
487+ */
488+ protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
489+ return false;
490+ }
491+}