933 lines
28 KiB
Java
933 lines
28 KiB
Java
/* IdentityHashMap.java -- a class providing a hashtable data structure,
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mapping Object --> Object, which uses object identity for hashing.
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Copyright (C) 2001, 2002 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util;
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import java.io.*;
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/**
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* This class provides a hashtable-backed implementation of the
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* Map interface, but uses object identity to do its hashing. In fact,
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* it uses object identity for comparing values, as well. It uses a
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* linear-probe hash table, which may have faster performance
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* than the chaining employed by HashMap.
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* <p>
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*
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* <em>WARNING: This is not a general purpose map. Because it uses
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* System.identityHashCode and ==, instead of hashCode and equals, for
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* comparison, it violated Map's general contract, and may cause
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* undefined behavior when compared to other maps which are not
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* IdentityHashMaps. This is designed only for the rare cases when
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* identity semantics are needed.</em> An example use is
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* topology-preserving graph transformations, such as deep cloning,
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* or as proxy object mapping such as in debugging.
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* <p>
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*
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* This map permits <code>null</code> keys and values, and does not
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* guarantee that elements will stay in the same order over time. The
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* basic operations (<code>get</code> and <code>put</code>) take
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* constant time, provided System.identityHashCode is decent. You can
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* tune the behavior by specifying the expected maximum size. As more
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* elements are added, the map may need to allocate a larger table,
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* which can be expensive.
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* <p>
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*
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* This implementation is unsynchronized. If you want multi-thread
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* access to be consistent, you must synchronize it, perhaps by using
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* <code>Collections.synchronizedMap(new IdentityHashMap(...));</code>.
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* The iterators are <i>fail-fast</i>, meaning that a structural modification
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* made to the map outside of an iterator's remove method cause the
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* iterator, and in the case of the entrySet, the Map.Entry, to
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* fail with a {@link ConcurrentModificationException}.
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*
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* @author Tom Tromey <tromey@redhat.com>
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* @author Eric Blake <ebb9@email.byu.edu>
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* @see System#identityHashCode(Object)
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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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* @see LinkedHashMap
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* @see WeakHashMap
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* @since 1.4
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* @status updated to 1.4
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*/
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public class IdentityHashMap extends AbstractMap
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implements Map, Serializable, Cloneable
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{
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/** The default capacity. */
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private static final int DEFAULT_CAPACITY = 21;
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/**
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* This object is used to mark deleted items. Package visible for use by
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* nested classes.
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*/
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static final Object tombstone = new Object();
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/**
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* This object is used to mark empty slots. We need this because
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* using null is ambiguous. Package visible for use by nested classes.
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*/
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static final Object emptyslot = new Object();
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/**
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* Compatible with JDK 1.4.
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*/
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private static final long serialVersionUID = 8188218128353913216L;
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/**
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* The number of mappings in the table. Package visible for use by nested
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* classes.
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* @serial
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*/
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int size;
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/**
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* The table itself. Package visible for use by nested classes.
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*/
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transient Object[] table;
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/**
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* The number of structural modifications made so far. Package visible for
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* use by nested classes.
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*/
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transient int modCount;
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/**
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* The cache for {@link #entrySet()}.
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*/
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private transient Set entries;
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/**
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* The threshold for rehashing, which is 75% of (table.length / 2).
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*/
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private transient int threshold;
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/**
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* Create a new IdentityHashMap with the default capacity (21 entries).
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*/
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public IdentityHashMap()
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{
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this(DEFAULT_CAPACITY);
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}
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/**
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* Create a new IdentityHashMap with the indicated number of
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* entries. If the number of elements added to this hash map
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* exceeds this maximum, the map will grow itself; however, that
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* incurs a performance penalty.
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*
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* @param max initial size
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* @throws IllegalArgumentException if max is negative
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*/
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public IdentityHashMap(int max)
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{
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if (max < 0)
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throw new IllegalArgumentException();
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// Need at least two slots, or hash() will break.
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if (max < 2)
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max = 2;
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table = new Object[max << 1];
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Arrays.fill(table, emptyslot);
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threshold = (max >> 2) * 3;
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}
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/**
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* Create a new IdentityHashMap whose contents are taken from the
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* given Map.
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*
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* @param m The map whose elements are to be put in this map
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* @throws NullPointerException if m is null
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*/
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public IdentityHashMap(Map m)
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{
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this(Math.max(m.size() << 1, DEFAULT_CAPACITY));
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putAll(m);
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}
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/**
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* Remove all mappings from this map.
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*/
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public void clear()
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{
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if (size != 0)
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{
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modCount++;
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Arrays.fill(table, emptyslot);
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size = 0;
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}
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}
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/**
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* Creates a shallow copy where keys and values are not cloned.
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*/
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public Object clone()
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{
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try
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{
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IdentityHashMap copy = (IdentityHashMap) super.clone();
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copy.table = (Object[]) table.clone();
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copy.entries = null; // invalidate the cache
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return copy;
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}
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catch (CloneNotSupportedException e)
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{
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// Can't happen.
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return null;
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}
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}
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/**
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* Tests whether the specified key is in this map. Unlike normal Maps,
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* this test uses <code>entry == key</code> instead of
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* <code>entry == null ? key == null : entry.equals(key)</code>.
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*
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* @param key the key to look for
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* @return true if the key is contained in the map
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* @see #containsValue(Object)
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* @see #get(Object)
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*/
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public boolean containsKey(Object key)
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{
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return key == table[hash(key)];
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}
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/**
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* Returns true if this HashMap contains the value. Unlike normal maps,
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* this test uses <code>entry == value</code> instead of
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* <code>entry == null ? value == null : entry.equals(value)</code>.
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*
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* @param value the value to search for in this HashMap
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* @return true if at least one key maps to the value
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* @see #containsKey(Object)
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*/
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public boolean containsValue(Object value)
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{
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for (int i = table.length - 1; i > 0; i -= 2)
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if (table[i] == value)
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return true;
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return false;
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}
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/**
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* Returns a "set view" of this Map's entries. The set is backed by
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* the Map, so changes in one show up in the other. The set supports
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* element removal, but not element addition.
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* <p>
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*
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* <em>The semantics of this set, and of its contained entries, are
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* different from the contract of Set and Map.Entry in order to make
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* IdentityHashMap work. This means that while you can compare these
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* objects between IdentityHashMaps, comparing them with regular sets
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* or entries is likely to have undefined behavior.</em> The entries
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* in this set are reference-based, rather than the normal object
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* equality. Therefore, <code>e1.equals(e2)</code> returns
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* <code>e1.getKey() == e2.getKey() && e1.getValue() == e2.getValue()</code>,
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* and <code>e.hashCode()</code> returns
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* <code>System.identityHashCode(e.getKey()) ^
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* System.identityHashCode(e.getValue())</code>.
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* <p>
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*
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* Note that the iterators for all three views, from keySet(), entrySet(),
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* and values(), traverse the Map in the same sequence.
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*
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* @return a set view of the entries
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* @see #keySet()
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* @see #values()
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* @see Map.Entry
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*/
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public Set entrySet()
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{
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if (entries == null)
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entries = new AbstractSet()
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{
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public int size()
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{
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return size;
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}
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public Iterator iterator()
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{
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return new IdentityIterator(ENTRIES);
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}
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public void clear()
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{
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IdentityHashMap.this.clear();
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}
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public boolean contains(Object o)
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{
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if (! (o instanceof Map.Entry))
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return false;
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Map.Entry m = (Map.Entry) o;
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return m.getValue() == table[hash(m.getKey()) + 1];
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}
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public int hashCode()
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{
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return IdentityHashMap.this.hashCode();
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}
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public boolean remove(Object o)
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{
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if (! (o instanceof Map.Entry))
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return false;
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Object key = ((Map.Entry) o).getKey();
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int h = hash(key);
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if (table[h] == key)
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{
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size--;
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modCount++;
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table[h] = tombstone;
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table[h + 1] = tombstone;
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return true;
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}
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return false;
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}
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};
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return entries;
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}
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/**
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* Compares two maps for equality. This returns true only if both maps
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* have the same reference-identity comparisons. While this returns
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* <code>this.entrySet().equals(m.entrySet())</code> as specified by Map,
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* this will not work with normal maps, since the entry set compares
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* with == instead of .equals.
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*
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* @param o the object to compare to
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* @return true if it is equal
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*/
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public boolean equals(Object o)
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{
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// Why did Sun specify this one? The superclass does the right thing.
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return super.equals(o);
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}
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/**
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* Return the value in this Map associated with the supplied key, or
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* <code>null</code> if the key maps to nothing.
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*
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* <p>NOTE: Since the value could also be null, you must use
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* containsKey to see if this key actually maps to something.
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* Unlike normal maps, this tests for the key with <code>entry ==
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* key</code> instead of <code>entry == null ? key == null :
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* entry.equals(key)</code>.
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*
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* @param key the key for which to fetch an associated value
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* @return what the key maps to, if present
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* @see #put(Object, Object)
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* @see #containsKey(Object)
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*/
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public Object get(Object key)
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{
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int h = hash(key);
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return table[h] == key ? table[h + 1] : null;
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}
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/**
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* Returns the hashcode of this map. This guarantees that two
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* IdentityHashMaps that compare with equals() will have the same hash code,
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* but may break with comparison to normal maps since it uses
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* System.identityHashCode() instead of hashCode().
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*
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* @return the hash code
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*/
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public int hashCode()
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{
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int hash = 0;
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for (int i = table.length - 2; i >= 0; i -= 2)
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{
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Object key = table[i];
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if (key == emptyslot || key == tombstone)
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continue;
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hash += (System.identityHashCode(key)
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^ System.identityHashCode(table[i + 1]));
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}
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return hash;
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}
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/**
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* Returns true if there are no key-value mappings currently in this Map
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* @return <code>size() == 0</code>
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*/
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public boolean isEmpty()
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{
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return size == 0;
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}
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/**
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* Returns a "set view" of this Map's keys. The set is backed by the
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* Map, so changes in one show up in the other. The set supports
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* element removal, but not element addition.
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* <p>
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*
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* <em>The semantics of this set are different from the contract of Set
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* in order to make IdentityHashMap work. This means that while you can
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* compare these objects between IdentityHashMaps, comparing them with
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* regular sets is likely to have undefined behavior.</em> The hashCode
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* of the set is the sum of the identity hash codes, instead of the
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* regular hashCodes, and equality is determined by reference instead
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* of by the equals method.
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* <p>
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*
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* @return a set view of the keys
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* @see #values()
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* @see #entrySet()
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*/
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public Set keySet()
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{
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if (keys == null)
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keys = new AbstractSet()
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{
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public int size()
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{
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return size;
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}
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public Iterator iterator()
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{
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return new IdentityIterator(KEYS);
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}
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public void clear()
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{
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IdentityHashMap.this.clear();
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}
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public boolean contains(Object o)
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{
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return containsKey(o);
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}
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public int hashCode()
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{
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int hash = 0;
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for (int i = table.length - 2; i >= 0; i -= 2)
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{
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Object key = table[i];
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if (key == emptyslot || key == tombstone)
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continue;
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hash += System.identityHashCode(key);
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}
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return hash;
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}
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public boolean remove(Object o)
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{
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int h = hash(o);
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if (table[h] == o)
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{
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size--;
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modCount++;
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table[h] = tombstone;
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table[h + 1] = tombstone;
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return true;
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}
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return false;
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}
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};
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return keys;
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}
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|
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/**
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* Puts the supplied value into the Map, mapped by the supplied key.
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* The value may be retrieved by any object which <code>equals()</code>
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* this key. NOTE: Since the prior value could also be null, you must
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* first use containsKey if you want to see if you are replacing the
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* key's mapping. Unlike normal maps, this tests for the key
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* with <code>entry == key</code> instead of
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* <code>entry == null ? key == null : entry.equals(key)</code>.
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|
*
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* @param key the key used to locate the value
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* @param value the value to be stored in the HashMap
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* @return the prior mapping of the key, or null if there was none
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* @see #get(Object)
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*/
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public Object put(Object key, Object value)
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{
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// Rehash if the load factor is too high.
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if (size > threshold)
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{
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Object[] old = table;
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// This isn't necessarily prime, but it is an odd number of key/value
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// slots, which has a higher probability of fewer collisions.
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table = new Object[old.length << 1 + 2];
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Arrays.fill(table, emptyslot);
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size = 0;
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threshold = (table.length >>> 3) * 3;
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|
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for (int i = old.length - 2; i >= 0; i -= 2)
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{
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Object oldkey = old[i];
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if (oldkey != tombstone && oldkey != emptyslot)
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// Just use put. This isn't very efficient, but it is ok.
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put(oldkey, old[i + 1]);
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}
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}
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int h = hash(key);
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if (table[h] == key)
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{
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Object r = table[h + 1];
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table[h + 1] = value;
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return r;
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}
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// At this point, we add a new mapping.
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modCount++;
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size++;
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table[h] = key;
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table[h + 1] = value;
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return null;
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}
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|
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/**
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* Copies all of the mappings from the specified map to this. If a key
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* is already in this map, its value is replaced.
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*
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* @param m the map to copy
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* @throws NullPointerException if m is null
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*/
|
|
public void putAll(Map m)
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{
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// Why did Sun specify this one? The superclass does the right thing.
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super.putAll(m);
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}
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|
|
/**
|
|
* Removes from the HashMap and returns the value which is mapped by
|
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* the supplied key. If the key maps to nothing, then the HashMap
|
|
* remains unchanged, and <code>null</code> is returned.
|
|
*
|
|
* NOTE: Since the value could also be null, you must use
|
|
* containsKey to see if you are actually removing a mapping.
|
|
* Unlike normal maps, this tests for the key with <code>entry ==
|
|
* key</code> instead of <code>entry == null ? key == null :
|
|
* entry.equals(key)</code>.
|
|
*
|
|
* @param key the key used to locate the value to remove
|
|
* @return whatever the key mapped to, if present
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|
*/
|
|
public Object remove(Object key)
|
|
{
|
|
int h = hash(key);
|
|
if (table[h] == key)
|
|
{
|
|
modCount++;
|
|
size--;
|
|
Object r = table[h + 1];
|
|
table[h] = tombstone;
|
|
table[h + 1] = tombstone;
|
|
return r;
|
|
}
|
|
return null;
|
|
}
|
|
|
|
/**
|
|
* Returns the number of kay-value mappings currently in this Map
|
|
* @return the size
|
|
*/
|
|
public int size()
|
|
{
|
|
return size;
|
|
}
|
|
|
|
/**
|
|
* Returns a "collection view" (or "bag view") of this Map's values.
|
|
* The collection is backed by the Map, so changes in one show up
|
|
* in the other. The collection supports element removal, but not element
|
|
* addition.
|
|
* <p>
|
|
*
|
|
* <em>The semantics of this set are different from the contract of
|
|
* Collection in order to make IdentityHashMap work. This means that
|
|
* while you can compare these objects between IdentityHashMaps, comparing
|
|
* them with regular sets is likely to have undefined behavior.</em>
|
|
* Likewise, contains and remove go by == instead of equals().
|
|
* <p>
|
|
*
|
|
* @return a bag view of the values
|
|
* @see #keySet()
|
|
* @see #entrySet()
|
|
*/
|
|
public Collection values()
|
|
{
|
|
if (values == null)
|
|
values = new AbstractCollection()
|
|
{
|
|
public int size()
|
|
{
|
|
return size;
|
|
}
|
|
|
|
public Iterator iterator()
|
|
{
|
|
return new IdentityIterator(VALUES);
|
|
}
|
|
|
|
public void clear()
|
|
{
|
|
IdentityHashMap.this.clear();
|
|
}
|
|
|
|
public boolean remove(Object o)
|
|
{
|
|
for (int i = table.length - 1; i > 0; i -= 2)
|
|
if (table[i] == o)
|
|
{
|
|
modCount++;
|
|
table[i - 1] = tombstone;
|
|
table[i] = tombstone;
|
|
size--;
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
};
|
|
return values;
|
|
}
|
|
|
|
/**
|
|
* Helper method which computes the hash code, then traverses the table
|
|
* until it finds the key, or the spot where the key would go.
|
|
*
|
|
* @param key the key to check
|
|
* @return the index where the key belongs
|
|
* @see #IdentityHashMap(int)
|
|
* @see #put(Object, Object)
|
|
*/
|
|
// Package visible for use by nested classes.
|
|
int hash(Object key)
|
|
{
|
|
// Implementation note: it is feasible for the table to have no
|
|
// emptyslots, if it is full with entries and tombstones, so we must
|
|
// remember where we started. If we encounter the key or an emptyslot,
|
|
// we are done. If we encounter a tombstone, the key may still be in
|
|
// the array. If we don't encounter the key, we use the first emptyslot
|
|
// or tombstone we encountered as the location where the key would go.
|
|
// By requiring at least 2 key/value slots, and rehashing at 75%
|
|
// capacity, we guarantee that there will always be either an emptyslot
|
|
// or a tombstone somewhere in the table.
|
|
int h = Math.abs(System.identityHashCode(key) % (table.length >> 1)) << 1;
|
|
int del = -1;
|
|
int save = h;
|
|
|
|
do
|
|
{
|
|
if (table[h] == key)
|
|
return h;
|
|
if (table[h] == emptyslot)
|
|
break;
|
|
if (table[h] == tombstone && del < 0)
|
|
del = h;
|
|
h -= 2;
|
|
if (h < 0)
|
|
h = table.length - 2;
|
|
}
|
|
while (h != save);
|
|
|
|
return del < 0 ? h : del;
|
|
}
|
|
|
|
/**
|
|
* This class allows parameterized iteration over IdentityHashMaps. Based
|
|
* on its construction, it returns the key or value of a mapping, or
|
|
* creates the appropriate Map.Entry object with the correct fail-fast
|
|
* semantics and identity comparisons.
|
|
*
|
|
* @author Tom Tromey <tromey@redhat.com>
|
|
* @author Eric Blake <ebb9@email.byu.edu>
|
|
*/
|
|
private final class IdentityIterator implements Iterator
|
|
{
|
|
/**
|
|
* The type of this Iterator: {@link #KEYS}, {@link #VALUES},
|
|
* or {@link #ENTRIES}.
|
|
*/
|
|
final int type;
|
|
/** The number of modifications to the backing Map that we know about. */
|
|
int knownMod = modCount;
|
|
/** The number of elements remaining to be returned by next(). */
|
|
int count = size;
|
|
/** Location in the table. */
|
|
int loc = table.length;
|
|
|
|
/**
|
|
* Construct a new Iterator with the supplied type.
|
|
* @param type {@link #KEYS}, {@link #VALUES}, or {@link #ENTRIES}
|
|
*/
|
|
IdentityIterator(int type)
|
|
{
|
|
this.type = type;
|
|
}
|
|
|
|
/**
|
|
* Returns true if the Iterator has more elements.
|
|
* @return true if there are more elements
|
|
* @throws ConcurrentModificationException if the Map was modified
|
|
*/
|
|
public boolean hasNext()
|
|
{
|
|
if (knownMod != modCount)
|
|
throw new ConcurrentModificationException();
|
|
return count > 0;
|
|
}
|
|
|
|
/**
|
|
* Returns the next element in the Iterator's sequential view.
|
|
* @return the next element
|
|
* @throws ConcurrentModificationException if the Map was modified
|
|
* @throws NoSuchElementException if there is none
|
|
*/
|
|
public Object next()
|
|
{
|
|
if (knownMod != modCount)
|
|
throw new ConcurrentModificationException();
|
|
if (count == 0)
|
|
throw new NoSuchElementException();
|
|
count--;
|
|
|
|
Object key;
|
|
do
|
|
{
|
|
loc -= 2;
|
|
key = table[loc];
|
|
}
|
|
while (key == emptyslot || key == tombstone);
|
|
|
|
return type == KEYS ? key : (type == VALUES ? table[loc + 1]
|
|
: new IdentityEntry(loc));
|
|
}
|
|
|
|
/**
|
|
* Removes from the backing Map the last element which was fetched
|
|
* with the <code>next()</code> method.
|
|
*
|
|
* @throws ConcurrentModificationException if the Map was modified
|
|
* @throws IllegalStateException if called when there is no last element
|
|
*/
|
|
public void remove()
|
|
{
|
|
if (knownMod != modCount)
|
|
throw new ConcurrentModificationException();
|
|
if (loc == table.length || table[loc] == tombstone)
|
|
throw new IllegalStateException();
|
|
modCount++;
|
|
size--;
|
|
table[loc] = tombstone;
|
|
table[loc + 1] = tombstone;
|
|
knownMod++;
|
|
}
|
|
} // class IdentityIterator
|
|
|
|
/**
|
|
* This class provides Map.Entry objects for IdentityHashMaps. The entry
|
|
* is fail-fast, and will throw a ConcurrentModificationException if
|
|
* the underlying map is modified, or if remove is called on the iterator
|
|
* that generated this object. It is identity based, so it violates
|
|
* the general contract of Map.Entry, and is probably unsuitable for
|
|
* comparison to normal maps; but it works among other IdentityHashMaps.
|
|
*
|
|
* @author Eric Blake <ebb9@email.byu.edu>
|
|
*/
|
|
private final class IdentityEntry implements Map.Entry
|
|
{
|
|
/** The location of this entry. */
|
|
final int loc;
|
|
/** The number of modifications to the backing Map that we know about. */
|
|
final int knownMod = modCount;
|
|
|
|
/**
|
|
* Constructs the Entry.
|
|
*
|
|
* @param loc the location of this entry in table
|
|
*/
|
|
IdentityEntry(int loc)
|
|
{
|
|
this.loc = loc;
|
|
}
|
|
|
|
/**
|
|
* Compares the specified object with this entry, using identity
|
|
* semantics. Note that this can lead to undefined results with
|
|
* Entry objects created by normal maps.
|
|
*
|
|
* @param o the object to compare
|
|
* @return true if it is equal
|
|
* @throws ConcurrentModificationException if the entry was invalidated
|
|
* by modifying the Map or calling Iterator.remove()
|
|
*/
|
|
public boolean equals(Object o)
|
|
{
|
|
if (knownMod != modCount || table[loc] == tombstone)
|
|
throw new ConcurrentModificationException();
|
|
if (! (o instanceof Map.Entry))
|
|
return false;
|
|
Map.Entry e = (Map.Entry) o;
|
|
return table[loc] == e.getKey() && table[loc + 1] == e.getValue();
|
|
}
|
|
|
|
/**
|
|
* Returns the key of this entry.
|
|
*
|
|
* @return the key
|
|
* @throws ConcurrentModificationException if the entry was invalidated
|
|
* by modifying the Map or calling Iterator.remove()
|
|
*/
|
|
public Object getKey()
|
|
{
|
|
if (knownMod != modCount || table[loc] == tombstone)
|
|
throw new ConcurrentModificationException();
|
|
return table[loc];
|
|
}
|
|
|
|
/**
|
|
* Returns the value of this entry.
|
|
*
|
|
* @return the value
|
|
* @throws ConcurrentModificationException if the entry was invalidated
|
|
* by modifying the Map or calling Iterator.remove()
|
|
*/
|
|
public Object getValue()
|
|
{
|
|
if (knownMod != modCount || table[loc] == tombstone)
|
|
throw new ConcurrentModificationException();
|
|
return table[loc + 1];
|
|
}
|
|
|
|
/**
|
|
* Returns the hashcode of the entry, using identity semantics.
|
|
* Note that this can lead to undefined results with Entry objects
|
|
* created by normal maps.
|
|
*
|
|
* @return the hash code
|
|
* @throws ConcurrentModificationException if the entry was invalidated
|
|
* by modifying the Map or calling Iterator.remove()
|
|
*/
|
|
public int hashCode()
|
|
{
|
|
if (knownMod != modCount || table[loc] == tombstone)
|
|
throw new ConcurrentModificationException();
|
|
return (System.identityHashCode(table[loc])
|
|
^ System.identityHashCode(table[loc + 1]));
|
|
}
|
|
|
|
/**
|
|
* Replaces the value of this mapping, and returns the old value.
|
|
*
|
|
* @param value the new value
|
|
* @return the old value
|
|
* @throws ConcurrentModificationException if the entry was invalidated
|
|
* by modifying the Map or calling Iterator.remove()
|
|
*/
|
|
public Object setValue(Object value)
|
|
{
|
|
if (knownMod != modCount || table[loc] == tombstone)
|
|
throw new ConcurrentModificationException();
|
|
Object r = table[loc + 1];
|
|
table[loc + 1] = value;
|
|
return r;
|
|
}
|
|
|
|
/**
|
|
* This provides a string representation of the entry. It is of the form
|
|
* "key=value", where string concatenation is used on key and value.
|
|
*
|
|
* @return the string representation
|
|
* @throws ConcurrentModificationException if the entry was invalidated
|
|
* by modifying the Map or calling Iterator.remove()
|
|
*/
|
|
public final String toString()
|
|
{
|
|
if (knownMod != modCount || table[loc] == tombstone)
|
|
throw new ConcurrentModificationException();
|
|
return table[loc] + "=" + table[loc + 1];
|
|
}
|
|
} // class IdentityEntry
|
|
|
|
/**
|
|
* Reads the object from a serial stream.
|
|
*
|
|
* @param s the stream to read from
|
|
* @throws ClassNotFoundException if the underlying stream fails
|
|
* @throws IOException if the underlying stream fails
|
|
* @serialData expects the size (int), followed by that many key (Object)
|
|
* and value (Object) pairs, with the pairs in no particular
|
|
* order
|
|
*/
|
|
private void readObject(ObjectInputStream s)
|
|
throws IOException, ClassNotFoundException
|
|
{
|
|
s.defaultReadObject();
|
|
|
|
int num = s.readInt();
|
|
table = new Object[Math.max(num << 1, DEFAULT_CAPACITY) << 1];
|
|
// Read key/value pairs.
|
|
while (--num >= 0)
|
|
put(s.readObject(), s.readObject());
|
|
}
|
|
|
|
/**
|
|
* Writes the object to a serial stream.
|
|
*
|
|
* @param s the stream to write to
|
|
* @throws IOException if the underlying stream fails
|
|
* @serialData outputs the size (int), followed by that many key (Object)
|
|
* and value (Object) pairs, with the pairs in no particular
|
|
* order
|
|
*/
|
|
private void writeObject(ObjectOutputStream s)
|
|
throws IOException
|
|
{
|
|
s.defaultWriteObject();
|
|
s.writeInt(size);
|
|
for (int i = table.length - 2; i >= 0; i -= 2)
|
|
{
|
|
Object key = table[i];
|
|
if (key != tombstone && key != emptyslot)
|
|
{
|
|
s.writeObject(key);
|
|
s.writeObject(table[i + 1]);
|
|
}
|
|
}
|
|
}
|
|
}
|