diff -r 5be31d9fa455 -r d382dacfd73f rt/emul/compact/src/main/java/java/util/LinkedHashMap.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/rt/emul/compact/src/main/java/java/util/LinkedHashMap.java Tue Feb 26 16:54:16 2013 +0100 @@ -0,0 +1,491 @@ +/* + * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. + * + * This code is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 only, as + * published by the Free Software Foundation. Oracle designates this + * particular file as subject to the "Classpath" exception as provided + * by Oracle in the LICENSE file that accompanied this code. + * + * This code is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License + * version 2 for more details (a copy is included in the LICENSE file that + * accompanied this code). + * + * You should have received a copy of the GNU General Public License version + * 2 along with this work; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. + * + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA + * or visit www.oracle.com if you need additional information or have any + * questions. + */ + +package java.util; +import java.io.*; + +/** + *
Hash table and linked list implementation of the Map interface, + * with predictable iteration order. This implementation differs from + * HashMap in that it maintains a doubly-linked list running through + * all of its entries. This linked list defines the iteration ordering, + * which is normally the order in which keys were inserted into the map + * (insertion-order). Note that insertion order is not affected + * if a key is re-inserted into the map. (A key k is + * reinserted into a map m if m.put(k, v) is invoked when + * m.containsKey(k) would return true immediately prior to + * the invocation.) + * + *
This implementation spares its clients from the unspecified, generally + * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}), + * without incurring the increased cost associated with {@link TreeMap}. It + * can be used to produce a copy of a map that has the same order as the + * original, regardless of the original map's implementation: + *
+ * void foo(Map m) { + * Map copy = new LinkedHashMap(m); + * ... + * } + *+ * This technique is particularly useful if a module takes a map on input, + * copies it, and later returns results whose order is determined by that of + * the copy. (Clients generally appreciate having things returned in the same + * order they were presented.) + * + *
A special {@link #LinkedHashMap(int,float,boolean) constructor} is + * provided to create a linked hash map whose order of iteration is the order + * in which its entries were last accessed, from least-recently accessed to + * most-recently (access-order). This kind of map is well-suited to + * building LRU caches. Invoking the put or get method + * results in an access to the corresponding entry (assuming it exists after + * the invocation completes). The putAll method generates one entry + * access for each mapping in the specified map, in the order that key-value + * mappings are provided by the specified map's entry set iterator. No + * other methods generate entry accesses. In particular, operations on + * collection-views do not affect the order of iteration of the backing + * map. + * + *
The {@link #removeEldestEntry(Map.Entry)} method may be overridden to + * impose a policy for removing stale mappings automatically when new mappings + * are added to the map. + * + *
This class provides all of the optional Map operations, and + * permits null elements. Like HashMap, it provides constant-time + * performance for the basic operations (add, contains and + * remove), assuming the hash function disperses elements + * properly among the buckets. Performance is likely to be just slightly + * below that of HashMap, due to the added expense of maintaining the + * linked list, with one exception: Iteration over the collection-views + * of a LinkedHashMap requires time proportional to the size + * of the map, regardless of its capacity. Iteration over a HashMap + * is likely to be more expensive, requiring time proportional to its + * capacity. + * + *
A linked hash map has two parameters that affect its performance: + * initial capacity and load factor. They are defined precisely + * as for HashMap. Note, however, that the penalty for choosing an + * excessively high value for initial capacity is less severe for this class + * than for HashMap, as iteration times for this class are unaffected + * by capacity. + * + *
Note that this implementation is not synchronized. + * If multiple threads access a linked hash map concurrently, and at least + * one of the threads modifies the map structurally, it must be + * synchronized externally. This is typically accomplished by + * synchronizing on some object that naturally encapsulates the map. + * + * If no such object exists, the map should be "wrapped" using the + * {@link Collections#synchronizedMap Collections.synchronizedMap} + * method. This is best done at creation time, to prevent accidental + * unsynchronized access to the map:
+ * Map m = Collections.synchronizedMap(new LinkedHashMap(...));+ * + * A structural modification is any operation that adds or deletes one or more + * mappings or, in the case of access-ordered linked hash maps, affects + * iteration order. In insertion-ordered linked hash maps, merely changing + * the value associated with a key that is already contained in the map is not + * a structural modification. In access-ordered linked hash maps, + * merely querying the map with get is a structural + * modification.) + * + *
The iterators returned by the iterator method of the collections + * returned by all of this class's collection view methods are + * fail-fast: if the map is structurally modified at any time after + * the iterator is created, in any way except through the iterator's own + * remove method, the iterator will throw a {@link + * ConcurrentModificationException}. Thus, in the face of concurrent + * modification, the iterator fails quickly and cleanly, rather than risking + * arbitrary, non-deterministic behavior at an undetermined time in the future. + * + *
Note that the fail-fast behavior of an iterator cannot be guaranteed + * as it is, generally speaking, impossible to make any hard guarantees in the + * presence of unsynchronized concurrent modification. Fail-fast iterators + * throw ConcurrentModificationException on a best-effort basis. + * Therefore, it would be wrong to write a program that depended on this + * exception for its correctness: the fail-fast behavior of iterators + * should be used only to detect bugs. + * + *
This class is a member of the
+ *
+ * Java Collections Framework.
+ *
+ * @param More formally, if this map contains a mapping from a key
+ * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
+ * key.equals(k))}, then this method returns {@code v}; otherwise
+ * it returns {@code null}. (There can be at most one such mapping.)
+ *
+ * A return value of {@code null} does not necessarily
+ * indicate that the map contains no mapping for the key; it's also
+ * possible that the map explicitly maps the key to {@code null}.
+ * The {@link #containsKey containsKey} operation may be used to
+ * distinguish these two cases.
+ */
+ public V get(Object key) {
+ Entry Sample use: this override will allow the map to grow up to 100
+ * entries and then delete the eldest entry each time a new entry is
+ * added, maintaining a steady state of 100 entries.
+ * This method typically does not modify the map in any way,
+ * instead allowing the map to modify itself as directed by its
+ * return value. It is permitted for this method to modify
+ * the map directly, but if it does so, it must return
+ * false (indicating that the map should not attempt any
+ * further modification). The effects of returning true
+ * after modifying the map from within this method are unspecified.
+ *
+ * This implementation merely returns false (so that this
+ * map acts like a normal map - the eldest element is never removed).
+ *
+ * @param eldest The least recently inserted entry in the map, or if
+ * this is an access-ordered map, the least recently accessed
+ * entry. This is the entry that will be removed it this
+ * method returns true. If the map was empty prior
+ * to the put or putAll invocation resulting
+ * in this invocation, this will be the entry that was just
+ * inserted; in other words, if the map contains a single
+ * entry, the eldest entry is also the newest.
+ * @return true if the eldest entry should be removed
+ * from the map; false if it should be retained.
+ */
+ protected boolean removeEldestEntry(Map.Entry
+ * private static final int MAX_ENTRIES = 100;
+ *
+ * protected boolean removeEldestEntry(Map.Entry eldest) {
+ * return size() > MAX_ENTRIES;
+ * }
+ *
+ *
+ *