3909N/A * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved. 0N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 0N/A * This code is free software; you can redistribute it and/or modify it 0N/A * under the terms of the GNU General Public License version 2 only, as 2362N/A * published by the Free Software Foundation. Oracle designates this 0N/A * particular file as subject to the "Classpath" exception as provided 2362N/A * by Oracle in the LICENSE file that accompanied this code. 0N/A * This code is distributed in the hope that it will be useful, but WITHOUT 0N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 0N/A * version 2 for more details (a copy is included in the LICENSE file that 0N/A * accompanied this code). 0N/A * You should have received a copy of the GNU General Public License version 0N/A * 2 along with this work; if not, write to the Free Software Foundation, 0N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 2362N/A * or visit www.oracle.com if you need additional information or have any 0N/A * <p>Hash table and linked list implementation of the <tt>Map</tt> interface, 0N/A * with predictable iteration order. This implementation differs from 0N/A * <tt>HashMap</tt> in that it maintains a doubly-linked list running through 0N/A * all of its entries. This linked list defines the iteration ordering, 0N/A * which is normally the order in which keys were inserted into the map 0N/A * (<i>insertion-order</i>). Note that insertion order is not affected 0N/A * if a key is <i>re-inserted</i> into the map. (A key <tt>k</tt> is 0N/A * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when 0N/A * <tt>m.containsKey(k)</tt> would return <tt>true</tt> immediately prior to 0N/A * <p>This implementation spares its clients from the unspecified, generally 0N/A * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}), 0N/A * without incurring the increased cost associated with {@link TreeMap}. It 0N/A * can be used to produce a copy of a map that has the same order as the 0N/A * original, regardless of the original map's implementation: 0N/A * Map copy = new LinkedHashMap(m); 0N/A * This technique is particularly useful if a module takes a map on input, 0N/A * copies it, and later returns results whose order is determined by that of 0N/A * the copy. (Clients generally appreciate having things returned in the same 0N/A * order they were presented.) 0N/A * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is 0N/A * provided to create a linked hash map whose order of iteration is the order 0N/A * in which its entries were last accessed, from least-recently accessed to 0N/A * most-recently (<i>access-order</i>). This kind of map is well-suited to 0N/A * building LRU caches. Invoking the <tt>put</tt> or <tt>get</tt> method 0N/A * results in an access to the corresponding entry (assuming it exists after 0N/A * the invocation completes). The <tt>putAll</tt> method generates one entry 0N/A * access for each mapping in the specified map, in the order that key-value 0N/A * mappings are provided by the specified map's entry set iterator. <i>No 0N/A * other methods generate entry accesses.</i> In particular, operations on 0N/A * collection-views do <i>not</i> affect the order of iteration of the backing 0N/A * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to 0N/A * impose a policy for removing stale mappings automatically when new mappings 0N/A * are added to the map. 0N/A * <p>This class provides all of the optional <tt>Map</tt> operations, and 0N/A * permits null elements. Like <tt>HashMap</tt>, it provides constant-time 0N/A * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and 0N/A * <tt>remove</tt>), assuming the hash function disperses elements 0N/A * properly among the buckets. Performance is likely to be just slightly 0N/A * below that of <tt>HashMap</tt>, due to the added expense of maintaining the 0N/A * linked list, with one exception: Iteration over the collection-views 0N/A * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i> 0N/A * of the map, regardless of its capacity. Iteration over a <tt>HashMap</tt> 0N/A * is likely to be more expensive, requiring time proportional to its 0N/A * <p>A linked hash map has two parameters that affect its performance: 0N/A * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely 0N/A * as for <tt>HashMap</tt>. Note, however, that the penalty for choosing an 0N/A * excessively high value for initial capacity is less severe for this class 0N/A * than for <tt>HashMap</tt>, as iteration times for this class are unaffected 0N/A * <p><strong>Note that this implementation is not synchronized.</strong> 0N/A * If multiple threads access a linked hash map concurrently, and at least 0N/A * one of the threads modifies the map structurally, it <em>must</em> be 0N/A * synchronized externally. This is typically accomplished by 0N/A * synchronizing on some object that naturally encapsulates the map. 0N/A * If no such object exists, the map should be "wrapped" using the 0N/A * {@link Collections#synchronizedMap Collections.synchronizedMap} 0N/A * method. This is best done at creation time, to prevent accidental 0N/A * unsynchronized access to the map:<pre> 0N/A * Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre> 0N/A * A structural modification is any operation that adds or deletes one or more 0N/A * mappings or, in the case of access-ordered linked hash maps, affects 0N/A * iteration order. In insertion-ordered linked hash maps, merely changing 0N/A * the value associated with a key that is already contained in the map is not 0N/A * a structural modification. <strong>In access-ordered linked hash maps, 0N/A * merely querying the map with <tt>get</tt> is a structural 0N/A * modification.</strong>) 0N/A * <p>The iterators returned by the <tt>iterator</tt> method of the collections 0N/A * returned by all of this class's collection view methods are 0N/A * <em>fail-fast</em>: if the map is structurally modified at any time after 0N/A * the iterator is created, in any way except through the iterator's own 0N/A * <tt>remove</tt> method, the iterator will throw a {@link 0N/A * ConcurrentModificationException}. Thus, in the face of concurrent 0N/A * modification, the iterator fails quickly and cleanly, rather than risking 0N/A * arbitrary, non-deterministic behavior at an undetermined time in the future. 0N/A * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 0N/A * as it is, generally speaking, impossible to make any hard guarantees in the 0N/A * presence of unsynchronized concurrent modification. Fail-fast iterators 0N/A * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 0N/A * Therefore, it would be wrong to write a program that depended on this 0N/A * exception for its correctness: <i>the fail-fast behavior of iterators 0N/A * should be used only to detect bugs.</i> 0N/A * <p>This class is a member of the 0N/A * Java Collections Framework</a>. 0N/A * @param <K> the type of keys maintained by this map 0N/A * @param <V> the type of mapped values 0N/A * @author Josh Bloch 0N/A * @see Object#hashCode() 0N/A * The head of the doubly linked list. 0N/A * The iteration ordering method for this linked hash map: <tt>true</tt> 0N/A * for access-order, <tt>false</tt> for insertion-order. 0N/A * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance 0N/A * with the specified initial capacity and load factor. 0N/A * @param initialCapacity the initial capacity 0N/A * @param loadFactor the load factor 0N/A * @throws IllegalArgumentException if the initial capacity is negative 0N/A * or the load factor is nonpositive 0N/A * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance 0N/A * with the specified initial capacity and a default load factor (0.75). 0N/A * @param initialCapacity the initial capacity 0N/A * @throws IllegalArgumentException if the initial capacity is negative 0N/A * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance 0N/A * with the default initial capacity (16) and load factor (0.75). 0N/A * Constructs an insertion-ordered <tt>LinkedHashMap</tt> instance with 0N/A * the same mappings as the specified map. The <tt>LinkedHashMap</tt> 0N/A * instance is created with a default load factor (0.75) and an initial 0N/A * capacity sufficient to hold the mappings in the specified map. 0N/A * @param m the map whose mappings are to be placed in this map 0N/A * @throws NullPointerException if the specified map is null 0N/A * Constructs an empty <tt>LinkedHashMap</tt> instance with the 0N/A * specified initial capacity, load factor and ordering mode. 0N/A * @param initialCapacity the initial capacity 0N/A * @param loadFactor the load factor 0N/A * @param accessOrder the ordering mode - <tt>true</tt> for 0N/A * access-order, <tt>false</tt> for insertion-order 0N/A * @throws IllegalArgumentException if the initial capacity is negative 0N/A * or the load factor is nonpositive 0N/A * Called by superclass constructors and pseudoconstructors (clone, 0N/A * readObject) before any entries are inserted into the map. Initializes 0N/A * Transfers all entries to new table array. This method is called 0N/A * by superclass resize. It is overridden for performance, as it is 0N/A * faster to iterate using our linked list. 0N/A * Returns <tt>true</tt> if this map maps one or more keys to the 0N/A * @param value value whose presence in this map is to be tested 0N/A * @return <tt>true</tt> if this map maps one or more keys to the 0N/A // Overridden to take advantage of faster iterator 0N/A * Returns the value to which the specified key is mapped, 0N/A * or {@code null} if this map contains no mapping for the key. 0N/A * <p>More formally, if this map contains a mapping from a key 0N/A * {@code k} to a value {@code v} such that {@code (key==null ? k==null : 0N/A * key.equals(k))}, then this method returns {@code v}; otherwise 0N/A * it returns {@code null}. (There can be at most one such mapping.) 0N/A * <p>A return value of {@code null} does not <i>necessarily</i> 0N/A * indicate that the map contains no mapping for the key; it's also 0N/A * possible that the map explicitly maps the key to {@code null}. 0N/A * The {@link #containsKey containsKey} operation may be used to 0N/A * distinguish these two cases. 0N/A * Removes all of the mappings from this map. 0N/A * The map will be empty after this call returns. 0N/A * LinkedHashMap entry. 0N/A // These fields comprise the doubly linked list used for iteration. 0N/A * Removes this entry from the linked list. 0N/A * Inserts this entry before the specified existing entry in the list. 0N/A * This method is invoked by the superclass whenever the value 0N/A * of a pre-existing entry is read by Map.get or modified by Map.set. 0N/A * If the enclosing Map is access-ordered, it moves the entry 0N/A * to the end of the list; otherwise, it does nothing. 0N/A * The modCount value that the iterator believes that the backing 0N/A * List should have. If this expectation is violated, the iterator 0N/A * has detected concurrent modification. 0N/A // These Overrides alter the behavior of superclass view iterator() methods 0N/A * This override alters behavior of superclass put method. It causes newly 0N/A * allocated entry to get inserted at the end of the linked list and 0N/A * removes the eldest entry if appropriate. 5047N/A // Remove eldest entry if instructed 0N/A * This override differs from addEntry in that it doesn't resize the 0N/A * table or remove the eldest entry. 0N/A * Returns <tt>true</tt> if this map should remove its eldest entry. 0N/A * This method is invoked by <tt>put</tt> and <tt>putAll</tt> after 0N/A * inserting a new entry into the map. It provides the implementor 0N/A * with the opportunity to remove the eldest entry each time a new one 0N/A * is added. This is useful if the map represents a cache: it allows 0N/A * the map to reduce memory consumption by deleting stale entries. 0N/A * <p>Sample use: this override will allow the map to grow up to 100 0N/A * entries and then delete the eldest entry each time a new entry is 0N/A * added, maintaining a steady state of 100 entries. 0N/A * private static final int MAX_ENTRIES = 100; 0N/A * protected boolean removeEldestEntry(Map.Entry eldest) { 0N/A * return size() > MAX_ENTRIES; 0N/A * <p>This method typically does not modify the map in any way, 0N/A * instead allowing the map to modify itself as directed by its 0N/A * return value. It <i>is</i> permitted for this method to modify 0N/A * the map directly, but if it does so, it <i>must</i> return 0N/A * <tt>false</tt> (indicating that the map should not attempt any 0N/A * further modification). The effects of returning <tt>true</tt> 0N/A * after modifying the map from within this method are unspecified. 0N/A * <p>This implementation merely returns <tt>false</tt> (so that this 0N/A * map acts like a normal map - the eldest element is never removed). 0N/A * @param eldest The least recently inserted entry in the map, or if 0N/A * this is an access-ordered map, the least recently accessed 0N/A * entry. This is the entry that will be removed it this 0N/A * method returns <tt>true</tt>. If the map was empty prior 0N/A * to the <tt>put</tt> or <tt>putAll</tt> invocation resulting 0N/A * in this invocation, this will be the entry that was just 0N/A * inserted; in other words, if the map contains a single 0N/A * entry, the eldest entry is also the newest. 0N/A * @return <tt>true</tt> if the eldest entry should be removed 0N/A * from the map; <tt>false</tt> if it should be retained.