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/* |
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* @(#)Hashtable.java 1.83 00/12/13 |
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* |
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* Copyright 1994-2002 Sun Microsystems, Inc. All Rights Reserved. |
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* |
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* This software is the proprietary information of Sun Microsystems, Inc. |
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* Use is subject to license terms. |
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* |
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*/ |
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package java.util; |
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import java.io.*; |
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/** |
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* This class implements a hashtable, which maps keys to values. Any |
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* non-<code>null</code> object can be used as a key or as a value. <p> |
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* |
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* To successfully store and retrieve objects from a hashtable, the |
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* objects used as keys must implement the <code>hashCode</code> |
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* method and the <code>equals</code> method. <p> |
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* |
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* An instance of <code>Hashtable</code> has two parameters that |
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* affect its performance: <i>initial capacity</i> and <i>load |
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* factor</i>. The <i>capacity</i> is the number of <i>buckets</i> in |
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* the hash table, and the <i>initial capacity</i> is simply the |
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* capacity at the time the hash table is created. Note that the hash |
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* table is <i>open</i>: in the case a "hash collision", a single |
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* bucket stores multiple entries, which must be searched |
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* sequentially. The <i>load factor</i> is a measure of how full the |
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* hash table is allowed to get before its capacity is automatically |
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* increased. When the number of entries in the hashtable exceeds the |
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* product of the load factor and the current capacity, the capacity |
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* is increased by calling the <code>rehash</code> method.<p> |
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* |
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* Generally, the default load factor (.75) offers a good tradeoff |
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* between time and space costs. Higher values decrease the space |
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* overhead but increase the time cost to look up an entry (which is |
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* reflected in most <tt>Hashtable</tt> operations, including |
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* <tt>get</tt> and <tt>put</tt>).<p> |
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* |
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* The initial capacity controls a tradeoff between wasted space and |
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* the need for <code>rehash</code> operations, which are |
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* time-consuming. No <code>rehash</code> operations will <i>ever</i> |
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* occur if the initial capacity is greater than the maximum number of |
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* entries the <tt>Hashtable</tt> will contain divided by its load |
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* factor. However, setting the initial capacity too high can waste |
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* space.<p> |
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* |
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* If many entries are to be made into a <code>Hashtable</code>, |
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* creating it with a sufficiently large capacity may allow the |
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* entries to be inserted more efficiently than letting it perform |
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* automatic rehashing as needed to grow the table. <p> |
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* |
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* This example creates a hashtable of numbers. It uses the names of |
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* the numbers as keys: |
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* <p><blockquote><pre> |
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* Hashtable numbers = new Hashtable(); |
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* numbers.put("one", new Integer(1)); |
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* numbers.put("two", new Integer(2)); |
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* numbers.put("three", new Integer(3)); |
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* </pre></blockquote> |
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* <p> |
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* To retrieve a number, use the following code: |
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* <p><blockquote><pre> |
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* Integer n = (Integer)numbers.get("two"); |
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* if (n != null) { |
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* System.out.println("two = " + n); |
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* } |
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* </pre></blockquote> |
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* <p> |
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* |
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* As of the Java 2 platform v1.2, this class has been retrofitted to |
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* implement Map, so that it becomes a part of Java's collection |
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* framework. Unlike the new collection implementations, Hashtable is |
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* fully thread-safe.<p> |
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* |
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* The Iterators returned by the iterator and listIterator methods of |
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* the Collections returned by all of Hashtable's "collection view |
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* methods" are <em>fail-fast</em>: if the Hashtable is structurally |
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* modified at any time after the Iterator is created, in any way |
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* except through the Iterator's own remove or add methods, the |
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* Iterator will throw a ConcurrentModificationException. Thus, in |
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* the face of concurrent modification, the Iterator fails quickly and |
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* cleanly, rather than risking arbitrary, non-deterministic behavior |
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* at an undetermined time in the future. The Enumerations returned |
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* by Hashtable's keys and values methods are <em>not</em> fail-fast. |
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* <p> |
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* |
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* @author Arthur van Hoff |
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* @author Josh Bloch |
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* @author Doug Lea |
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* @version 1.83, 12/13/00 |
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* @see Object#equals(java.lang.Object) |
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* @see Object#hashCode() |
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* @see Hashtable#rehash() |
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* @see Collection |
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* @see Map |
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* @see HashMap |
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* @see TreeMap |
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* @since JDK1.0 |
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*/ |
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public class Hashtable extends Dictionary |
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implements Map, Cloneable, Serializable { |
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/* |
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* This implementation is thread-safe, but not heavily |
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* synchronized. The basic strategy is to ensure that the hash |
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* table and its lists are ALWAYS kept in a consistent state, so |
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* can be read without locking. Next fields of nodes are |
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* immutable (final). All list additions are performed at the |
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* front of each bin. This makes it easy to check changes, and |
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* also fast to traverse. When nodes would otherwise be changed, |
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* new nodes are created to replace them. This works well for hash |
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* tables since the bin lists tend to be short. (The average |
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* length is less than two for the default load factor threshold.) |
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* |
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* Read operations can thus proceed without locking, but rely on a |
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* memory barrier to ensure that COMPLETED write operations |
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* performed by other threads are noticed. Conveniently, the |
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* "count" field, tracking the number of elements, can also serve |
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* as the volatile variable providing proper read/write |
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* barriers. This is convenient because this field needs to be |
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* read in many read operations anyway. The use of volatiles for |
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* this purpose is only guaranteed to work in accord with normal |
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* expectations in multithreaded environments when run on JVMs |
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* conforming to the clarified JSR133 memory model specification. |
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* This true for hotspot as of release 1.4. |
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* |
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* Implementors note. The basic rules for all this are: |
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* - All unsynchronized read operations must first read |
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* the "count" field, and generally, should not look at table if 0. |
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* |
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* - All synchronized write operations should write to |
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* the "count" field after updating. The operations may not |
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* take any action that could even momentarily cause |
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* a concurrent read operation to see inconsistent |
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* data. This is made easier by the nature of the read |
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* operations in Hashtable. For example, no operation |
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* can reveal that the table has grown but the threshold |
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* has not yet been updated, so there are no atomicity |
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* requirements for this with respect to reads. |
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* |
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* As a guide, all critical volatile reads and writes are marked |
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* in the code as comments. |
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*/ |
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/** use serialVersionUID from JDK 1.0.2 for interoperability */ |
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private static final long serialVersionUID = 1421746759512286392L; |
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/** |
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* The default initial number of table slots for this table (32). |
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* Used when not otherwise specified in constructor. |
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*/ |
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static int DEFAULT_INITIAL_CAPACITY = 16; |
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/** |
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* The maximum capacity, used if a higher value is implicitly |
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* specified by either of the constructors with arguments. MUST |
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* be a power of two <= 1<<30. |
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*/ |
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static final int MAXIMUM_CAPACITY = 1 << 30; |
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/** |
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* The default load factor for this table. Used when not |
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* otherwise specified in constructor. |
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*/ |
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static final float DEFAULT_LOAD_FACTOR = 0.75f; |
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/** |
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* The total number of mappings in the hash table. |
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* Also serves as the read-barrier variable. |
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*/ |
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private transient volatile int count; |
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/** |
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* The hash table data. |
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*/ |
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private transient Entry[] table; |
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/** |
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* The load factor for the hash table. This is also used as a |
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* recursion flag in method hashCode. (Sorry for the sleaze but |
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* this maintains 1.1 compatibility.) |
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* |
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* @serial |
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*/ |
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private float loadFactor; |
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/** |
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* The table is rehashed when its size exceeds this threshold. |
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* (The value of this field is always (int)(capacity * |
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* loadFactor).) |
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* |
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* @serial |
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*/ |
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private int threshold; |
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/** |
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* The number of times this map has been structurally modified |
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* Structural modifications are those that change the number of |
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* mappings in the map or otherwise modify its internal structure |
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* (e.g., rehash). This field is used to make iterators on |
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* Collection-views of the map fail-fast. (See |
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* ConcurrentModificationException). |
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*/ |
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private transient int modCount; |
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// internal utilities |
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/** |
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* Return a hash code for non-null Object x. |
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*/ |
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private static int hash(Object x) { |
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int h = x.hashCode(); |
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h += ~(h << 9); |
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h ^= (h >>> 14); |
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h += (h << 4); |
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h ^= (h >>> 10); |
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return h; |
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} |
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/** |
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* Check for equality of non-null references x and y. |
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**/ |
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private static boolean eq(Object x, Object y) { |
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return x == y || x.equals(y); |
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} |
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/** |
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* Return index for hash code h. |
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*/ |
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private static int indexFor(int h, int length) { |
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return h & (length-1); |
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} |
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/** |
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* Set table to new Entry array. |
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* Call only while holding lock or in constructor. |
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**/ |
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private void setTable(Entry[] newTable) { |
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table = newTable; |
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threshold = (int)(newTable.length * loadFactor); |
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count = count; // write-volatile |
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} |
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/** |
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* Constructs a new, empty map with a default initial capacity |
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* and load factor. |
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*/ |
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public Hashtable() { |
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loadFactor = DEFAULT_LOAD_FACTOR; |
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setTable(new Entry[DEFAULT_INITIAL_CAPACITY]); |
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} |
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/** |
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* Constructs a new, empty map with the specified initial |
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* capacity and the specified load factor. |
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* |
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* @param initialCapacity the initial capacity |
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* The actual initial capacity is rounded to the nearest power of two. |
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* @param loadFactor the load factor of the Hashtable |
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* @throws IllegalArgumentException if the initial capacity is less |
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* than zero, or if the load factor is nonpositive. |
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*/ |
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public Hashtable(int initialCapacity, float loadFactor) { |
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if (initialCapacity < 0) |
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throw new IllegalArgumentException("Illegal initial capacity: " + |
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initialCapacity); |
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if (loadFactor <= 0 || Float.isNaN(loadFactor)) |
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throw new IllegalArgumentException("Illegal Load factor: "+ |
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loadFactor); |
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this.loadFactor = loadFactor; |
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int capacity; |
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if (initialCapacity > MAXIMUM_CAPACITY) |
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capacity = MAXIMUM_CAPACITY; |
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else { |
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capacity = 1; |
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while (capacity < initialCapacity) |
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capacity <<= 1; |
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} |
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setTable(new Entry[capacity]); |
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} |
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/** |
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* Constructs a new, empty map with the specified initial |
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* capacity and default load factor. |
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* |
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* @param initialCapacity the initial capacity of the |
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* Hashtable. |
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* The actual initial capacity is rounded to the nearest power of two. |
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* @throws IllegalArgumentException if the initial maximum number |
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* of elements is less |
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* than zero. |
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*/ |
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public Hashtable(int initialCapacity) { |
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this(initialCapacity, DEFAULT_LOAD_FACTOR); |
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} |
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/** |
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* Constructs a new map with the same mappings as the given map. The |
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* map is created with a default load factor. |
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*/ |
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public Hashtable(Map t) { |
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this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1, 16), |
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DEFAULT_LOAD_FACTOR); |
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putAll(t); |
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} |
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/** |
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* Returns the number of key-value mappings in this map. |
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* |
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* @return the number of key-value mappings in this map. |
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*/ |
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public int size() { |
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return count; // read-volatile |
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} |
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/** |
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* Returns <tt>true</tt> if this map contains no key-value mappings. |
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* |
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* @return <tt>true</tt> if this map contains no key-value mappings. |
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*/ |
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public boolean isEmpty() { |
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return count == 0; // read-volatile |
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} |
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/** |
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* Returns the value to which the specified key is mapped in this table. |
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* |
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* @param key a key in the table. |
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* @return the value to which the key is mapped in this table; |
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* <code>null</code> if the key is not mapped to any value in |
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* this table. |
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* @exception NullPointerException if the key is |
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* <code>null</code>. |
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* @see #put(Object, Object) |
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*/ |
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public Object get(Object key) { |
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int hash = hash(key); // throws NullPointerException if key null |
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if (count != 0) { // read-volatile |
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Entry[] tab = table; |
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int index = indexFor(hash, tab.length); |
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Entry e = tab[index]; |
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while (e != null) { |
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if (e.hash == hash && eq(key, e.key)) |
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return e.value; |
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e = e.next; |
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} |
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} |
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return null; |
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} |
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/** |
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* Tests if the specified object is a key in this table. |
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* |
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* @param key possible key. |
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* @return <code>true</code> if and only if the specified object |
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* is a key in this table, as determined by the |
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* <tt>equals</tt> method; <code>false</code> otherwise. |
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* @exception NullPointerException if the key is |
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* <code>null</code>. |
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* @see #contains(Object) |
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*/ |
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public boolean containsKey(Object key) { |
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int hash = hash(key); // throws NullPointerException if key null |
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if (count != 0) { // read-volatile |
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Entry[] tab = table; |
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int index = indexFor(hash, tab.length); |
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Entry e = tab[index]; |
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while (e != null) { |
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if (e.hash == hash && eq(key, e.key)) |
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return true; |
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e = e.next; |
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} |
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} |
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return false; |
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} |
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/** |
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* Returns <tt>true</tt> if this map maps one or more keys to the |
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* specified value. Note: This method requires a full internal |
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* traversal of the hash table, and so is much slower than |
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* method <tt>containsKey</tt>. |
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* |
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|
|
* @param value value whose presence in this map is to be tested. |
395 |
|
|
* @return <tt>true</tt> if this map maps one or more keys to the |
396 |
|
|
* specified value. |
397 |
|
|
* @exception NullPointerException if the value is <code>null</code>. |
398 |
|
|
*/ |
399 |
|
|
public boolean containsValue(Object value) { |
400 |
|
|
if (value == null) |
401 |
|
|
throw new NullPointerException(); |
402 |
|
|
|
403 |
|
|
if (count != 0) { |
404 |
|
|
Entry tab[] = table; |
405 |
|
|
int len = tab.length; |
406 |
|
|
for (int i = 0 ; i < len; i++) |
407 |
|
|
for (Entry e = tab[i] ; e != null ; e = e.next) |
408 |
|
|
if (value.equals(e.value)) |
409 |
|
|
return true; |
410 |
|
|
} |
411 |
|
|
return false; |
412 |
|
|
} |
413 |
|
|
|
414 |
|
|
|
415 |
|
|
/** |
416 |
|
|
* Tests if some key maps into the specified value in this table. |
417 |
|
|
* This operation is more expensive than the <code>containsKey</code> |
418 |
|
|
* method.<p> |
419 |
|
|
* |
420 |
|
|
* Note that this method is identical in functionality to containsValue, |
421 |
|
|
* (which is part of the Map interface in the collections framework). |
422 |
|
|
* |
423 |
|
|
* @param value a value to search for. |
424 |
|
|
* @return <code>true</code> if and only if some key maps to the |
425 |
|
|
* <code>value</code> argument in this table as |
426 |
|
|
* determined by the <tt>equals</tt> method; |
427 |
|
|
* <code>false</code> otherwise. |
428 |
|
|
* @exception NullPointerException if the value is <code>null</code>. |
429 |
|
|
* @see #containsKey(Object) |
430 |
|
|
* @see #containsValue(Object) |
431 |
|
|
* @see Map |
432 |
|
|
*/ |
433 |
|
|
public boolean contains(Object value) { |
434 |
|
|
return containsValue(value); |
435 |
|
|
} |
436 |
|
|
|
437 |
|
|
/** |
438 |
|
|
* Maps the specified <code>key</code> to the specified |
439 |
|
|
* <code>value</code> in this table. Neither the key nor the |
440 |
|
|
* value can be <code>null</code>. <p> |
441 |
|
|
* |
442 |
|
|
* The value can be retrieved by calling the <code>get</code> method |
443 |
|
|
* with a key that is equal to the original key. |
444 |
|
|
* |
445 |
|
|
* @param key the table key. |
446 |
|
|
* @param value the value. |
447 |
|
|
* @return the previous value of the specified key in this table, |
448 |
|
|
* or <code>null</code> if it did not have one. |
449 |
|
|
* @exception NullPointerException if the key or value is |
450 |
|
|
* <code>null</code>. |
451 |
|
|
* @see Object#equals(Object) |
452 |
|
|
* @see #get(Object) |
453 |
|
|
*/ |
454 |
|
|
public synchronized Object put(Object key, Object value) { |
455 |
|
|
if (value == null) |
456 |
|
|
throw new NullPointerException(); |
457 |
|
|
int hash = hash(key); |
458 |
|
|
Entry[] tab = table; |
459 |
|
|
int index = indexFor(hash, tab.length); |
460 |
|
|
Entry first = tab[index]; |
461 |
|
|
|
462 |
|
|
for (Entry e = first; e != null; e = e.next) { |
463 |
|
|
if (e.hash == hash && eq(key, e.key)) { |
464 |
|
|
Object oldValue = e.value; |
465 |
|
|
e.value = value; |
466 |
|
|
count = count; // write-volatile |
467 |
|
|
return oldValue; |
468 |
|
|
} |
469 |
|
|
} |
470 |
|
|
|
471 |
|
|
tab[index] = new Entry(hash, key, value, first); |
472 |
|
|
modCount++; |
473 |
|
|
if (++count > threshold) // write-volatile |
474 |
|
|
rehash(); |
475 |
|
|
return null; |
476 |
|
|
} |
477 |
|
|
|
478 |
|
|
public synchronized Object putIfAbsent(Object key, Object value) { |
479 |
|
|
if (value == null) |
480 |
|
|
throw new NullPointerException(); |
481 |
|
|
int hash = hash(key); |
482 |
|
|
Entry[] tab = table; |
483 |
|
|
int index = indexFor(hash, tab.length); |
484 |
|
|
Entry first = tab[index]; |
485 |
|
|
|
486 |
|
|
for (Entry e = first; e != null; e = e.next) { |
487 |
|
|
if (e.hash == hash && eq(key, e.key)) { |
488 |
|
|
Object oldValue = e.value; |
489 |
|
|
count = count; // write-volatile |
490 |
|
|
return oldValue; |
491 |
|
|
} |
492 |
|
|
} |
493 |
|
|
|
494 |
|
|
tab[index] = new Entry(hash, key, value, first); |
495 |
|
|
modCount++; |
496 |
|
|
if (++count > threshold) // write-volatile |
497 |
|
|
rehash(); |
498 |
|
|
return value; |
499 |
|
|
} |
500 |
|
|
|
501 |
|
|
/** |
502 |
|
|
* Rehashes the contents of this map into a new table |
503 |
|
|
* with a larger capacity. This method is called automatically when the |
504 |
|
|
* number of keys in this map exceeds the load factor threshold. |
505 |
|
|
*/ |
506 |
|
|
private void rehash() { |
507 |
|
|
Entry[] oldTable = table; |
508 |
|
|
int oldCapacity = oldTable.length; |
509 |
|
|
if (oldCapacity < MAXIMUM_CAPACITY) { |
510 |
|
|
Entry[] newTable = new Entry[oldCapacity << 1]; |
511 |
|
|
transfer(oldTable, newTable); |
512 |
|
|
setTable(newTable); |
513 |
|
|
} |
514 |
|
|
} |
515 |
|
|
|
516 |
|
|
/** |
517 |
|
|
* Transfer nodes from old table to new table. |
518 |
|
|
*/ |
519 |
|
|
private static void transfer(Entry[] oldTable, Entry[] newTable) { |
520 |
|
|
/* |
521 |
|
|
* Reclassify nodes in each list to new Map. Because we are |
522 |
|
|
* using power-of-two expansion, the elements from each bin |
523 |
|
|
* must either stay at same index, or move with a power of two |
524 |
|
|
* offset. We eliminate unnecessary node creation by catching |
525 |
|
|
* cases where old nodes can be reused because their next |
526 |
|
|
* fields won't change. Statistically, at the default |
527 |
|
|
* threshhold, only about one-sixth of them need cloning when |
528 |
|
|
* a table doubles. The nodes they replace will be garbage |
529 |
|
|
* collectable as soon as they are no longer referenced by any |
530 |
|
|
* reader thread that may be in the midst of traversing table |
531 |
|
|
* right now. |
532 |
|
|
*/ |
533 |
|
|
|
534 |
|
|
int oldCapacity = oldTable.length; |
535 |
|
|
int mask = newTable.length - 1; |
536 |
|
|
for (int i = 0; i < oldCapacity ; i++) { |
537 |
|
|
// We need to guarantee that any existing reads of old Map can |
538 |
|
|
// proceed. So we cannot yet null out each bin. |
539 |
|
|
Entry e = oldTable[i]; |
540 |
|
|
|
541 |
|
|
if (e != null) { |
542 |
|
|
Entry next = e.next; |
543 |
|
|
int idx = e.hash & mask; |
544 |
|
|
|
545 |
|
|
// Single node on list |
546 |
|
|
if (next == null) |
547 |
|
|
newTable[idx] = e; |
548 |
|
|
|
549 |
|
|
else { |
550 |
|
|
// Reuse trailing consecutive sequence at same slot |
551 |
|
|
Entry lastRun = e; |
552 |
|
|
int lastIdx = idx; |
553 |
|
|
for (Entry last = next; last != null; last = last.next) { |
554 |
|
|
int k = last.hash & mask; |
555 |
|
|
if (k != lastIdx) { |
556 |
|
|
lastIdx = k; |
557 |
|
|
lastRun = last; |
558 |
|
|
} |
559 |
|
|
} |
560 |
|
|
newTable[lastIdx] = lastRun; |
561 |
|
|
|
562 |
|
|
// Clone all remaining nodes |
563 |
|
|
for (Entry p = e; p != lastRun; p = p.next) { |
564 |
|
|
int k = p.hash & mask; |
565 |
|
|
newTable[k] = new Entry(p.hash, p.key, |
566 |
|
|
p.value, newTable[k]); |
567 |
|
|
} |
568 |
|
|
} |
569 |
|
|
} |
570 |
|
|
} |
571 |
|
|
} |
572 |
|
|
|
573 |
|
|
|
574 |
|
|
/** |
575 |
|
|
* Copies all of the mappings from the specified map to this one. |
576 |
|
|
* |
577 |
|
|
* These mappings replace any mappings that this map had for any of the |
578 |
|
|
* keys currently in the specified Map. |
579 |
|
|
* |
580 |
|
|
* @param t Mappings to be stored in this map. |
581 |
|
|
*/ |
582 |
|
|
|
583 |
|
|
public void putAll(Map t) { |
584 |
|
|
int n = t.size(); |
585 |
|
|
// Expand enough to hold at least n elements without resizing. |
586 |
|
|
if (n >= threshold) |
587 |
|
|
resizeToFit(n); |
588 |
|
|
|
589 |
|
|
for (Iterator it = t.entrySet().iterator(); it.hasNext(); ) { |
590 |
|
|
Map.Entry e = (Map.Entry) it.next(); |
591 |
|
|
put(e.getKey(), e.getValue()); |
592 |
|
|
} |
593 |
|
|
} |
594 |
|
|
|
595 |
|
|
/** |
596 |
|
|
* Resize by enough to fit n elements. |
597 |
|
|
*/ |
598 |
|
|
private synchronized void resizeToFit(int n) { |
599 |
|
|
int newSize = (int)(n / loadFactor + 1); |
600 |
|
|
if (newSize > MAXIMUM_CAPACITY) |
601 |
|
|
newSize = MAXIMUM_CAPACITY; |
602 |
|
|
|
603 |
|
|
Entry[] oldTable = table; |
604 |
|
|
int oldCapacity = oldTable.length; |
605 |
|
|
int newCapacity = oldCapacity; |
606 |
|
|
while (newCapacity < newSize) |
607 |
|
|
newCapacity <<= 1; |
608 |
|
|
|
609 |
|
|
if (newCapacity > oldCapacity) { |
610 |
|
|
Entry[] newTable = new Entry[newCapacity]; |
611 |
|
|
if (count != 0) |
612 |
|
|
transfer(oldTable, newTable); |
613 |
|
|
setTable(newTable); |
614 |
|
|
} |
615 |
|
|
} |
616 |
|
|
|
617 |
|
|
|
618 |
|
|
/** |
619 |
|
|
* Removes the key (and its corresponding value) from this |
620 |
|
|
* table. This method does nothing if the key is not in the table. |
621 |
|
|
* |
622 |
|
|
* @param key the key that needs to be removed. |
623 |
|
|
* @return the value to which the key had been mapped in this table, |
624 |
|
|
* or <code>null</code> if the key did not have a mapping. |
625 |
|
|
* @exception NullPointerException if the key is |
626 |
|
|
* <code>null</code>. |
627 |
|
|
*/ |
628 |
|
|
public synchronized Object remove(Object key) { |
629 |
|
|
int hash = hash(key); |
630 |
|
|
Entry[] tab = table; |
631 |
|
|
int index = indexFor(hash, tab.length); |
632 |
|
|
Entry first = tab[index]; |
633 |
|
|
|
634 |
|
|
Entry e = first; |
635 |
|
|
while (true) { |
636 |
|
|
if (e == null) |
637 |
|
|
return e; |
638 |
|
|
if (e.hash == hash && eq(key, e.key)) |
639 |
|
|
break; |
640 |
|
|
e = e.next; |
641 |
|
|
} |
642 |
|
|
|
643 |
|
|
// All entries following removed node can stay in list, but |
644 |
|
|
// all preceeding ones need to be cloned. |
645 |
|
|
Entry newFirst = e.next; |
646 |
|
|
for (Entry p = first; p != e; p = p.next) |
647 |
|
|
newFirst = new Entry(p.hash, p.key, p.value, newFirst); |
648 |
|
|
tab[index] = newFirst; |
649 |
|
|
|
650 |
|
|
modCount++; |
651 |
|
|
count--; // write-volatile |
652 |
|
|
return e.value; |
653 |
|
|
} |
654 |
|
|
|
655 |
|
|
|
656 |
|
|
/** |
657 |
|
|
* Helper method for entrySet.remove |
658 |
|
|
*/ |
659 |
|
|
private synchronized boolean findAndRemoveEntry(Object key, |
660 |
|
|
Object value) { |
661 |
|
|
return key != null && value != null && |
662 |
|
|
value.equals(get(key)) && (remove(key) != null); |
663 |
|
|
} |
664 |
|
|
|
665 |
|
|
/** |
666 |
|
|
* Removes all mappings from this map. |
667 |
|
|
*/ |
668 |
|
|
public synchronized void clear() { |
669 |
|
|
modCount++; |
670 |
|
|
Entry tab[] = table; |
671 |
|
|
int len = tab.length; |
672 |
|
|
for (int i = 0; i < len ; i++) |
673 |
|
|
tab[i] = null; |
674 |
|
|
count = 0; // write-volatile |
675 |
|
|
} |
676 |
|
|
|
677 |
|
|
|
678 |
|
|
/** |
679 |
|
|
* Returns a string representation of this <tt>Hashtable</tt> object |
680 |
|
|
* in the form of a set of entries, enclosed in braces and separated |
681 |
|
|
* by the ASCII characters "<tt>, </tt>" (comma and space). Each |
682 |
|
|
* entry is rendered as the key, an equals sign <tt>=</tt>, and the |
683 |
|
|
* associated element, where the <tt>toString</tt> method is used to |
684 |
|
|
* convert the key and element to strings. <p>Overrides to |
685 |
|
|
* <tt>toString</tt> method of <tt>Object</tt>. |
686 |
|
|
* |
687 |
|
|
* @return a string representation of this hashtable. |
688 |
|
|
*/ |
689 |
|
|
public String toString() { |
690 |
|
|
if (count == 0) // read-volatile |
691 |
|
|
return "{}"; |
692 |
|
|
|
693 |
|
|
StringBuffer buf = new StringBuffer(); |
694 |
|
|
buf.append("{"); |
695 |
|
|
|
696 |
|
|
Entry tab[] = table; |
697 |
|
|
int len = tab.length; |
698 |
|
|
int k = 0; |
699 |
|
|
for (int i = 0 ; i < len; i++) { |
700 |
|
|
for (Entry e = tab[i] ; e != null ; e = e.next) { |
701 |
|
|
if (k++ != 0) |
702 |
|
|
buf.append(", "); |
703 |
|
|
Object key = e.getKey(); |
704 |
|
|
Object value = e.getValue(); |
705 |
|
|
|
706 |
|
|
buf.append((key == this ? "(this Map)" : key) + "=" + |
707 |
|
|
(value == this ? "(this Map)": value)); |
708 |
|
|
} |
709 |
|
|
} |
710 |
|
|
buf.append("}"); |
711 |
|
|
return buf.toString(); |
712 |
|
|
} |
713 |
|
|
|
714 |
|
|
/** |
715 |
|
|
* Compares the specified Object with this Map for equality, |
716 |
|
|
* as per the definition in the Map interface. |
717 |
|
|
* |
718 |
|
|
* @return true if the specified Object is equal to this Map. |
719 |
|
|
* @see Map#equals(Object) |
720 |
|
|
* @since 1.2 |
721 |
|
|
*/ |
722 |
|
|
public boolean equals(Object o) { |
723 |
|
|
if (o == this) |
724 |
|
|
return true; |
725 |
|
|
if (!(o instanceof Map)) |
726 |
|
|
return false; |
727 |
|
|
|
728 |
|
|
Map t = (Map) o; |
729 |
|
|
if (t.size() != count) // read-volatile |
730 |
|
|
return false; |
731 |
|
|
|
732 |
|
|
Entry tab[] = table; |
733 |
|
|
int len = tab.length; |
734 |
|
|
for (int i = 0 ; i < len; i++) { |
735 |
|
|
for (Entry e = tab[i] ; e != null ; e = e.next) { |
736 |
|
|
Object v = t.get(e.key); |
737 |
|
|
if (v == null || !v.equals(e.value)) |
738 |
|
|
return false; |
739 |
|
|
} |
740 |
|
|
} |
741 |
|
|
return true; |
742 |
|
|
} |
743 |
|
|
|
744 |
|
|
/** |
745 |
|
|
* Returns the hash code value for this Map as per the definition in the |
746 |
|
|
* Map interface. |
747 |
|
|
* |
748 |
|
|
* @see Map#hashCode() |
749 |
|
|
* @since 1.2 |
750 |
|
|
*/ |
751 |
|
|
public synchronized int hashCode() { |
752 |
|
|
/* |
753 |
|
|
This implementation maintains compatibility with |
754 |
|
|
JDK1.1 to allow computing hashCodes for Hashtables |
755 |
|
|
with reference cycles. This requires both synchronization |
756 |
|
|
and temporary abuse of the "loadFactor" field to signify |
757 |
|
|
that a hashCode is in the midst of being computed so |
758 |
|
|
to ignore recursive calls. It is embarassing |
759 |
|
|
to use loadFactor in this way, but this tactic permits |
760 |
|
|
handling the case without any other field changes. |
761 |
|
|
|
762 |
|
|
Even though hashCodes of cyclic structures can be computed, |
763 |
|
|
programs should NOT insert a Hashtable into itself. Because |
764 |
|
|
its hashCode changes as a result of entering itself, it is |
765 |
|
|
normally impossible to retrieve the embedded Hashtable using |
766 |
|
|
get(). |
767 |
|
|
*/ |
768 |
|
|
int h = 0; |
769 |
|
|
float lf = loadFactor; |
770 |
|
|
if (count != 0 && lf > 0) { |
771 |
|
|
loadFactor = 0; // zero as recursion flag |
772 |
|
|
Entry tab[] = table; |
773 |
|
|
int len = tab.length; |
774 |
|
|
for (int i = 0 ; i < len; i++) |
775 |
|
|
for (Entry e = tab[i] ; e != null ; e = e.next) |
776 |
|
|
h += e.key.hashCode() ^ e.value.hashCode(); |
777 |
|
|
loadFactor = lf; |
778 |
|
|
} |
779 |
|
|
return h; |
780 |
|
|
} |
781 |
|
|
|
782 |
|
|
|
783 |
|
|
/** |
784 |
|
|
* Returns a shallow copy of this |
785 |
|
|
* <tt>Hashtable</tt> instance: the keys and |
786 |
|
|
* values themselves are not cloned. |
787 |
|
|
* |
788 |
|
|
* @return a shallow copy of this map. |
789 |
|
|
*/ |
790 |
|
|
public synchronized Object clone() { |
791 |
|
|
Hashtable result = null; |
792 |
|
|
try { |
793 |
|
|
result = (Hashtable)super.clone(); |
794 |
|
|
} |
795 |
|
|
catch (CloneNotSupportedException e) { |
796 |
|
|
// assert false; |
797 |
|
|
} |
798 |
|
|
result.count = 0; |
799 |
|
|
result.keySet = null; |
800 |
|
|
result.entrySet = null; |
801 |
|
|
result.values = null; |
802 |
|
|
result.modCount = 0; |
803 |
|
|
result.table = new Entry[table.length]; |
804 |
|
|
result.putAll(this); |
805 |
|
|
return result; |
806 |
|
|
} |
807 |
|
|
|
808 |
|
|
/** |
809 |
|
|
* Hashtable collision list entry. |
810 |
|
|
*/ |
811 |
|
|
private static class Entry implements Map.Entry { |
812 |
|
|
private final Object key; |
813 |
|
|
private Object value; |
814 |
|
|
private final int hash; |
815 |
|
|
private final Entry next; |
816 |
|
|
|
817 |
|
|
Entry(int hash, Object key, Object value, Entry next) { |
818 |
|
|
this.value = value; |
819 |
|
|
this.hash = hash; |
820 |
|
|
this.key = key; |
821 |
|
|
this.next = next; |
822 |
|
|
} |
823 |
|
|
|
824 |
|
|
public Object getKey() { |
825 |
|
|
return key; |
826 |
|
|
} |
827 |
|
|
|
828 |
|
|
public Object getValue() { |
829 |
|
|
return value; |
830 |
|
|
} |
831 |
|
|
|
832 |
|
|
public Object setValue(Object newValue) { |
833 |
|
|
// We aren't required to, and don't provide any |
834 |
|
|
// visibility barriers for setting value. |
835 |
|
|
if (newValue == null) |
836 |
|
|
throw new NullPointerException(); |
837 |
|
|
Object oldValue = this.value; |
838 |
|
|
this.value = newValue; |
839 |
|
|
return oldValue; |
840 |
|
|
} |
841 |
|
|
|
842 |
|
|
public boolean equals(Object o) { |
843 |
|
|
if (!(o instanceof Map.Entry)) |
844 |
|
|
return false; |
845 |
|
|
Map.Entry e = (Map.Entry)o; |
846 |
|
|
return (key.equals(e.getKey()) && value.equals(e.getValue())); |
847 |
|
|
} |
848 |
|
|
|
849 |
|
|
public int hashCode() { |
850 |
|
|
return key.hashCode() ^ value.hashCode(); |
851 |
|
|
} |
852 |
|
|
|
853 |
|
|
public String toString() { |
854 |
|
|
return key + "=" + value; |
855 |
|
|
} |
856 |
|
|
} |
857 |
|
|
|
858 |
|
|
/** |
859 |
|
|
* Support for Enumeration interface. These Enumerations take a |
860 |
|
|
* snapshot of table, so can never encounter corrupted |
861 |
|
|
* representations in multithreaded programs. At worst, they will |
862 |
|
|
* report the presence of entries deleted since the enumeration |
863 |
|
|
* was constructed, or absence of those inserted. |
864 |
|
|
*/ |
865 |
|
|
private static class Enumerator implements Enumeration { |
866 |
|
|
Entry next; // next entry to return |
867 |
|
|
final Entry[] tab; // snapshot of table |
868 |
|
|
int index; // current slot |
869 |
|
|
final boolean returnKeys; |
870 |
|
|
|
871 |
|
|
Enumerator(boolean returnKeys, int size, Entry[] t) { |
872 |
|
|
this.returnKeys = returnKeys; |
873 |
|
|
tab = t; |
874 |
|
|
int i = t.length; |
875 |
|
|
Entry n = null; |
876 |
|
|
if (size != 0) { // advance to first entry |
877 |
|
|
while (i > 0 && (n = tab[--i]) == null) |
878 |
|
|
; |
879 |
|
|
} |
880 |
|
|
next = n; |
881 |
|
|
index = i; |
882 |
|
|
} |
883 |
|
|
|
884 |
|
|
public boolean hasMoreElements() { |
885 |
|
|
return next != null; |
886 |
|
|
} |
887 |
|
|
|
888 |
|
|
public Object nextElement() { |
889 |
|
|
Entry e = next; |
890 |
|
|
if (e == null) |
891 |
|
|
throw new NoSuchElementException("Hashtable Enumerator"); |
892 |
|
|
|
893 |
|
|
Entry n = e.next; |
894 |
|
|
int i = index; |
895 |
|
|
while (n == null && i > 0) |
896 |
|
|
n = tab[--i]; |
897 |
|
|
index = i; |
898 |
|
|
next = n; |
899 |
|
|
return returnKeys? e.key : e.value; |
900 |
|
|
} |
901 |
|
|
} |
902 |
|
|
|
903 |
|
|
private static final int KEYS = 0; |
904 |
|
|
private static final int VALUES = 1; |
905 |
|
|
private static final int ENTRIES = 2; |
906 |
|
|
|
907 |
|
|
/** |
908 |
|
|
* Support for Iterator interface. |
909 |
|
|
*/ |
910 |
|
|
private class HashIterator implements Iterator { |
911 |
|
|
Entry next; // next entry to return |
912 |
|
|
int expectedModCount; // For fast-fail |
913 |
|
|
int index; // current slot |
914 |
|
|
Entry current; // current entry |
915 |
|
|
final int returnType; // KEYS or VALUES or ENTRIES |
916 |
|
|
|
917 |
|
|
HashIterator(int returnType) { |
918 |
|
|
this.returnType = returnType; |
919 |
|
|
int size = count; // read-volatile |
920 |
|
|
Entry[] t = table; |
921 |
|
|
expectedModCount = modCount; |
922 |
|
|
int i = t.length; |
923 |
|
|
Entry n = null; |
924 |
|
|
if (size != 0) { // advance to first entry |
925 |
|
|
while (i > 0 && (n = t[--i]) == null) |
926 |
|
|
; |
927 |
|
|
} |
928 |
|
|
next = n; |
929 |
|
|
index = i; |
930 |
|
|
} |
931 |
|
|
|
932 |
|
|
public boolean hasNext() { |
933 |
|
|
return next != null; |
934 |
|
|
} |
935 |
|
|
|
936 |
|
|
public Object next() { |
937 |
|
|
int ignore = count; // read-volatile |
938 |
|
|
if (modCount != expectedModCount) |
939 |
|
|
throw new ConcurrentModificationException(); |
940 |
|
|
Entry e = next; |
941 |
|
|
if (e == null) |
942 |
|
|
throw new NoSuchElementException("Hashtable Enumerator"); |
943 |
|
|
|
944 |
|
|
Entry n = e.next; |
945 |
|
|
Entry[] t = table; |
946 |
|
|
int i = index; |
947 |
|
|
while (n == null && i > 0) |
948 |
|
|
n = t[--i]; |
949 |
|
|
index = i; |
950 |
|
|
next = n; |
951 |
|
|
current = e; |
952 |
|
|
return (returnType == KEYS)? e.key : |
953 |
|
|
((returnType == VALUES)? e.value : e); |
954 |
|
|
} |
955 |
|
|
|
956 |
|
|
public void remove() { |
957 |
|
|
if (current == null) |
958 |
|
|
throw new IllegalStateException("Hashtable Enumerator"); |
959 |
|
|
Object k = current.key; |
960 |
|
|
current = null; |
961 |
|
|
if (Hashtable.this.remove(k) == null) |
962 |
|
|
throw new ConcurrentModificationException(); |
963 |
|
|
expectedModCount = modCount; |
964 |
|
|
} |
965 |
|
|
} |
966 |
|
|
|
967 |
|
|
|
968 |
|
|
// Views |
969 |
|
|
|
970 |
|
|
private transient Set keySet = null; |
971 |
|
|
private transient Set entrySet = null; |
972 |
|
|
private transient Collection values = null; |
973 |
|
|
|
974 |
|
|
/** |
975 |
|
|
* Returns a set view of the keys contained in this map. The set is |
976 |
|
|
* backed by the map, so changes to the map are reflected in the set, and |
977 |
|
|
* vice-versa. The set supports element removal, which removes the |
978 |
|
|
* corresponding mapping from this map, via the <tt>Iterator.remove</tt>, |
979 |
|
|
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and |
980 |
|
|
* <tt>clear</tt> operations. It does not support the <tt>add</tt> or |
981 |
|
|
* <tt>addAll</tt> operations. |
982 |
|
|
* |
983 |
|
|
* @return a set view of the keys contained in this map. |
984 |
|
|
*/ |
985 |
|
|
|
986 |
|
|
public Set keySet() { |
987 |
|
|
Set ks = keySet; |
988 |
|
|
return (ks != null)? ks : (keySet = new KeySet()); |
989 |
|
|
} |
990 |
|
|
|
991 |
|
|
private class KeySet extends AbstractSet { |
992 |
|
|
public Iterator iterator() { |
993 |
|
|
return new HashIterator(KEYS); |
994 |
|
|
} |
995 |
|
|
public int size() { |
996 |
|
|
return Hashtable.this.size(); |
997 |
|
|
} |
998 |
|
|
public boolean contains(Object o) { |
999 |
|
|
return Hashtable.this.containsKey(o); |
1000 |
|
|
} |
1001 |
|
|
public boolean remove(Object o) { |
1002 |
|
|
return Hashtable.this.remove(o) != null; |
1003 |
|
|
} |
1004 |
|
|
public void clear() { |
1005 |
|
|
Hashtable.this.clear(); |
1006 |
|
|
} |
1007 |
|
|
} |
1008 |
|
|
|
1009 |
|
|
/** |
1010 |
|
|
* Returns a collection view of the values contained in this map. The |
1011 |
|
|
* collection is backed by the map, so changes to the map are reflected in |
1012 |
|
|
* the collection, and vice-versa. The collection supports element |
1013 |
|
|
* removal, which removes the corresponding mapping from this map, via the |
1014 |
|
|
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
1015 |
|
|
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
1016 |
|
|
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
1017 |
|
|
* |
1018 |
|
|
* @return a collection view of the values contained in this map. |
1019 |
|
|
*/ |
1020 |
|
|
|
1021 |
|
|
public Collection values() { |
1022 |
|
|
Collection vs = values; |
1023 |
|
|
return (vs != null)? vs : (values = new Values()); |
1024 |
|
|
} |
1025 |
|
|
|
1026 |
|
|
private class Values extends AbstractCollection { |
1027 |
|
|
public Iterator iterator() { |
1028 |
|
|
return new HashIterator(VALUES); |
1029 |
|
|
} |
1030 |
|
|
public int size() { |
1031 |
|
|
return Hashtable.this.size(); |
1032 |
|
|
} |
1033 |
|
|
public boolean contains(Object o) { |
1034 |
|
|
return Hashtable.this.containsValue(o); |
1035 |
|
|
} |
1036 |
|
|
public void clear() { |
1037 |
|
|
Hashtable.this.clear(); |
1038 |
|
|
} |
1039 |
|
|
} |
1040 |
|
|
|
1041 |
|
|
/** |
1042 |
|
|
* Returns a collection view of the mappings contained in this map. Each |
1043 |
|
|
* element in the returned collection is a <tt>Map.Entry</tt>. The |
1044 |
|
|
* collection is backed by the map, so changes to the map are reflected in |
1045 |
|
|
* the collection, and vice-versa. The collection supports element |
1046 |
|
|
* removal, which removes the corresponding mapping from the map, via the |
1047 |
|
|
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
1048 |
|
|
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
1049 |
|
|
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
1050 |
|
|
* |
1051 |
|
|
* @return a collection view of the mappings contained in this map. |
1052 |
|
|
* @see Map.Entry |
1053 |
|
|
*/ |
1054 |
|
|
|
1055 |
|
|
public Set entrySet() { |
1056 |
|
|
Set es = entrySet; |
1057 |
|
|
return (es != null) ? es : (entrySet = new EntrySet()); |
1058 |
|
|
} |
1059 |
|
|
|
1060 |
|
|
private class EntrySet extends AbstractSet { |
1061 |
|
|
public Iterator iterator() { |
1062 |
|
|
return new HashIterator(ENTRIES); |
1063 |
|
|
} |
1064 |
|
|
public boolean contains(Object o) { |
1065 |
|
|
if (!(o instanceof Map.Entry)) |
1066 |
|
|
return false; |
1067 |
|
|
Map.Entry entry = (Map.Entry)o; |
1068 |
|
|
Object v = Hashtable.this.get(entry.getKey()); |
1069 |
|
|
return v != null && v.equals(entry.getValue()); |
1070 |
|
|
} |
1071 |
|
|
public boolean remove(Object o) { |
1072 |
|
|
if (!(o instanceof Map.Entry)) |
1073 |
|
|
return false; |
1074 |
|
|
Map.Entry entry = (Map.Entry)o; |
1075 |
|
|
return Hashtable.this.findAndRemoveEntry(entry.getKey(), |
1076 |
|
|
entry.getValue()); |
1077 |
|
|
} |
1078 |
|
|
public int size() { |
1079 |
|
|
return Hashtable.this.size(); |
1080 |
|
|
} |
1081 |
|
|
public void clear() { |
1082 |
|
|
Hashtable.this.clear(); |
1083 |
|
|
} |
1084 |
|
|
} |
1085 |
|
|
|
1086 |
|
|
/** |
1087 |
|
|
* Returns an enumeration of the keys in this table. |
1088 |
|
|
* |
1089 |
|
|
* @return an enumeration of the keys in this table. |
1090 |
|
|
* @see Enumeration |
1091 |
|
|
* @see #elements() |
1092 |
|
|
* @see #keySet() |
1093 |
|
|
* @see Map |
1094 |
|
|
*/ |
1095 |
|
|
public Enumeration keys() { |
1096 |
|
|
int n = count; // read-volatile |
1097 |
|
|
return new Enumerator(true, n, table); |
1098 |
|
|
} |
1099 |
|
|
|
1100 |
|
|
/** |
1101 |
|
|
* Returns an enumeration of the values in this table. |
1102 |
|
|
* Use the Enumeration methods on the returned object to fetch the elements |
1103 |
|
|
* sequentially. |
1104 |
|
|
* |
1105 |
|
|
* @return an enumeration of the values in this table. |
1106 |
|
|
* @see java.util.Enumeration |
1107 |
|
|
* @see #keys() |
1108 |
|
|
* @see #values() |
1109 |
|
|
* @see Map |
1110 |
|
|
*/ |
1111 |
|
|
|
1112 |
|
|
public Enumeration elements() { |
1113 |
|
|
int n = count; // read-volatile |
1114 |
|
|
return new Enumerator(false, n, table); |
1115 |
|
|
} |
1116 |
|
|
|
1117 |
|
|
/** |
1118 |
|
|
* Save the state of the <tt>Hashtable</tt> |
1119 |
|
|
* instance to a stream (i.e., |
1120 |
|
|
* serialize it). |
1121 |
|
|
* |
1122 |
|
|
* @serialData The <i>capacity</i> of the |
1123 |
|
|
* Hashtable (the length of the |
1124 |
|
|
* bucket array) is emitted (int), followed by the |
1125 |
|
|
* <i>size</i> of the Hashtable (the number of key-value |
1126 |
|
|
* mappings), followed by the key (Object) and value (Object) |
1127 |
|
|
* for each key-value mapping represented by the Hashtable |
1128 |
|
|
* The key-value mappings are emitted in no particular order. |
1129 |
|
|
*/ |
1130 |
|
|
|
1131 |
|
|
private synchronized void writeObject(java.io.ObjectOutputStream s) |
1132 |
|
|
throws IOException { |
1133 |
|
|
// Write out the threshold, loadfactor, and any hidden stuff |
1134 |
|
|
s.defaultWriteObject(); |
1135 |
|
|
|
1136 |
|
|
// Write out number of buckets |
1137 |
|
|
s.writeInt(table.length); |
1138 |
|
|
|
1139 |
|
|
// Write out size (number of Mappings) |
1140 |
|
|
s.writeInt(count); |
1141 |
|
|
|
1142 |
|
|
// Write out keys and values (alternating) |
1143 |
|
|
for (int index = table.length-1; index >= 0; index--) { |
1144 |
|
|
Entry entry = table[index]; |
1145 |
|
|
|
1146 |
|
|
while (entry != null) { |
1147 |
|
|
s.writeObject(entry.key); |
1148 |
|
|
s.writeObject(entry.value); |
1149 |
|
|
entry = entry.next; |
1150 |
|
|
} |
1151 |
|
|
} |
1152 |
|
|
} |
1153 |
|
|
|
1154 |
|
|
/** |
1155 |
|
|
* Reconstitute the <tt>Hashtable</tt> |
1156 |
|
|
* instance from a stream (i.e., |
1157 |
|
|
* deserialize it). |
1158 |
|
|
*/ |
1159 |
|
|
private synchronized void readObject(java.io.ObjectInputStream s) |
1160 |
|
|
throws IOException, ClassNotFoundException { |
1161 |
|
|
// Read in the threshold, loadfactor, and any hidden stuff |
1162 |
|
|
s.defaultReadObject(); |
1163 |
|
|
|
1164 |
|
|
// Read in number of buckets and allocate the bucket array; |
1165 |
|
|
int numBuckets = s.readInt(); |
1166 |
|
|
table = new Entry[numBuckets]; |
1167 |
|
|
|
1168 |
|
|
// Read in size (number of Mappings) |
1169 |
|
|
int size = s.readInt(); |
1170 |
|
|
|
1171 |
|
|
// Read the keys and values, and put the mappings in the table |
1172 |
|
|
for (int i=0; i<size; i++) { |
1173 |
|
|
Object key = s.readObject(); |
1174 |
|
|
Object value = s.readObject(); |
1175 |
|
|
put(key, value); |
1176 |
|
|
} |
1177 |
|
|
} |
1178 |
|
|
|
1179 |
|
|
} |