mirror of git://gcc.gnu.org/git/gcc.git
859 lines
24 KiB
Java
859 lines
24 KiB
Java
/* HashMap.java -- a class providing a basic hashtable data structure,
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mapping Object --> Object
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Copyright (C) 1998, 1999, 2000 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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As a special exception, if you link this library with other files to
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produce an executable, this library does not by itself cause the
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resulting executable to be covered by the GNU General Public License.
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This exception does not however invalidate any other reasons why the
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executable file might be covered by the GNU General Public License. */
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package java.util;
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import java.io.IOException;
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import java.io.Serializable;
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import java.io.ObjectInputStream;
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import java.io.ObjectOutputStream;
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import java.io.ObjectStreamField;
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/**
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* This class provides a hashtable-backed implementation of the
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* Map interface.
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*
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* It uses a hash-bucket approach; that is, hash
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* collisions are handled by linking the new node off of the
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* pre-existing node (or list of nodes). In this manner, techniques
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* such as linear probing (which can casue primary clustering) and
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* rehashing (which does not fit very well with Java's method of
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* precomputing hash codes) are avoided.
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*
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* Under ideal circumstances (no collisions, HashMap offers O(1)
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* performance on most operations (<pre>containsValue()</pre> is,
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* of course, O(n)). In the worst case (all keys map to the same
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* hash code -- very unlikely), most operations are O(n).
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*
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* HashMap is part of the JDK1.2 Collections API. It differs from
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* Hashtable in that it accepts the null key and null values, and it
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* does not support "Enumeration views."
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*
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* @author Jon Zeppieri
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* @version $Revision: 1.6 $
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* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
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*/
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public class HashMap extends AbstractMap
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implements Map, Cloneable, Serializable
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{
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// STATIC (CLASS) VARIABLES ------------------------------------------
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/**
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* the default capacity for an instance of HashMap -- I think this
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* is low, and perhaps it shoudl be raised; Sun's documentation mildly
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* suggests that this (11) is the correct value, though
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*/
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private static final int DEFAULT_CAPACITY = 11;
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/** the default load factor of a HashMap */
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private static final float DEFAULT_LOAD_FACTOR = 0.75F;
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/** used internally to represent the null key */
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private static final HashMap.Null NULL_KEY = new HashMap.Null();
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/** used internally to parameterize the creation of set/collection views */
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private static final int KEYS = 0;
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/** used internally to parameterize the creation of set/collection views */
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private static final int VALUES = 1;
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/** used internally to parameterize the creation of set/collection views */
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private static final int ENTRIES = 2;
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private static final long serialVersionUID = 362498820763181265L;
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// INSTANCE VARIABLES -------------------------------------------------
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/** the capacity of this HashMap: denotes the size of the bucket array */
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transient int capacity;
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/** the size of this HashMap: denotes the number of key-value pairs */
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private transient int size;
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/** the load factor of this HashMap: used in computing the threshold
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* @serial
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*/
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float loadFactor;
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/* the rounded product of the capacity and the load factor; when the number of
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* elements exceeds the threshold, the HashMap calls <pre>rehash()</pre>
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* @serial
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*/
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private int threshold;
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/**
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* this data structure contains the actual key-value mappings; a
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* <pre>BucketList</pre> is a lightweight linked list of "Buckets",
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* which, in turn, are linked nodes containing a key-value mapping
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* and a reference to the "next" Bucket in the list
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*/
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private transient Bucket[] buckets;
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/**
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* counts the number of modifications this HashMap has undergone; used by Iterators
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* to know when to throw ConcurrentModificationExceptions (idea ripped-off from
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* Stuart Ballard's AbstractList implementation)
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*/
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private transient int modCount;
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// CONSTRUCTORS ---------------------------------------------------------
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/**
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* construct a new HashMap with the default capacity and the default
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* load factor
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*/
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public HashMap()
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{
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init(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR);
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}
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/**
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* construct a new HashMap with a specific inital capacity and load factor
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*
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* @param initialCapacity the initial capacity of this HashMap (>=0)
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* @param initialLoadFactor the load factor of this HashMap
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* (a misnomer, really, since the load factor of
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* a HashMap does not change)
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*
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* @throws IllegalArgumentException if (initialCapacity < 0) ||
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* (initialLoadFactor > 1.0) ||
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* (initialLoadFactor <= 0.0)
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*/
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public HashMap(int initialCapacity, float initialLoadFactor)
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throws IllegalArgumentException
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{
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if (initialCapacity < 0 || initialLoadFactor <= 0 || initialLoadFactor > 1)
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throw new IllegalArgumentException();
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else
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init(initialCapacity, initialLoadFactor);
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}
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/**
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* construct a new HashMap with a specific inital capacity
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*
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* @param initialCapacity the initial capacity of this HashMap (>=0)
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*
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* @throws IllegalArgumentException if (initialCapacity < 0)
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*/
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public HashMap(int initialCapacity)
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throws IllegalArgumentException
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{
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if (initialCapacity < 0)
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throw new IllegalArgumentException();
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else
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init(initialCapacity, DEFAULT_LOAD_FACTOR);
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}
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/**
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* construct a new HashMap from the given Map
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*
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* every element in Map t will be put into this new HashMap
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*
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* @param t a Map whose key / value pairs will be put into
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* the new HashMap. <b>NOTE: key / value pairs
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* are not cloned in this constructor</b>
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*/
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public HashMap(Map t)
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{
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int mapSize = t.size() * 2;
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init(((mapSize > DEFAULT_CAPACITY) ? mapSize : DEFAULT_CAPACITY), DEFAULT_LOAD_FACTOR);
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putAll(t);
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}
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// PUBLIC METHODS ---------------------------------------------------------
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/** returns the number of kay-value mappings currently in this Map */
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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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/** returns true if there are no key-value mappings currently in this Map */
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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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/** empties this HashMap of all elements */
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public void clear()
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{
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size = 0;
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modCount++;
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buckets = new Bucket[capacity];
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}
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/**
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* returns a shallow clone of this HashMap (i.e. the Map itself is cloned, but
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* its contents are not)
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*/
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public Object clone()
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{
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Map.Entry entry;
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Iterator it = entrySet().iterator();
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HashMap clone = new HashMap(capacity, loadFactor);
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while (it.hasNext())
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{
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entry = (Map.Entry) it.next();
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clone.internalPut(entry.getKey(), entry.getValue());
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}
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return clone;
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}
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/** returns a "set view" of this HashMap's keys */
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public Set keySet()
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{
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return new HashMapSet(KEYS);
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}
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/** returns a "set view" of this HashMap's entries */
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public Set entrySet()
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{
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return new HashMapSet(ENTRIES);
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}
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/** returns a "collection view" (or "bag view") of this HashMap's values */
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public Collection values()
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{
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return new HashMapCollection();
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}
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/**
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* returns true if the supplied object equals (<pre>equals()</pre>) a key
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* in this HashMap
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*
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* @param key the key to search for in this HashMap
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*/
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public boolean containsKey(Object key)
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{
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return (internalGet(key) != null);
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}
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/**
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* returns true if this HashMap contains a value <pre>o</pre>, such that
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* <pre>o.equals(value)</pre>.
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*
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* @param value the value to search for in this Hashtable
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*/
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public boolean containsValue(Object value)
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{
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int i;
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Bucket list;
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for (i = 0; i < capacity; i++)
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{
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list = buckets[i];
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if (list != null && list.containsValue(value))
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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 the value in this Hashtable associated with the supplied key, or <pre>null</pre>
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* if the key maps to nothing
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*
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* @param key the key for which to fetch an associated value
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*/
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public Object get(Object key)
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{
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Map.Entry oResult = internalGet(key);
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return (oResult == null) ? null : oResult.getValue();
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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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*
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* @param key the HashMap key used to locate the value
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* @param value the value to be stored in the HashMap
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*/
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public Object put(Object key, Object value)
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{
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return internalPut(key, value);
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}
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/**
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* removes from the HashMap and returns the value which is mapped by the
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* supplied key; if the key maps to nothing, then the HashMap remains unchanged,
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* and <pre>null</pre> is returned
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*
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* @param key the key used to locate the value to remove from the HashMap
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*/
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public Object remove(Object key)
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{
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Bucket list;
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int index;
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Object result = null;
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if (size > 0)
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{
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index = hash(((key == null) ? NULL_KEY : key));
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list = buckets[index];
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if (list != null)
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{
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result = list.removeByKey(key);
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if (result != null)
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{
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size--;
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modCount++;
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if (list.first == null)
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buckets[index] = null;
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}
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}
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}
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return result;
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}
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// PRIVATE METHODS -----------------------------------------------------------
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/**
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* puts the given key-value pair into this HashMap; a private method is used
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* because it is called by the rehash() method as well as the put() method,
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* and if a subclass overrides put(), then rehash would do funky things
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* if it called put()
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*
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* @param key the HashMap key used to locate the value
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* @param value the value to be stored in the HashMap
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*/
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private Object internalPut(Object key, Object value)
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{
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HashMapEntry entry;
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Bucket list;
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int hashIndex;
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Object oResult;
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Object oRealKey = ((key == null) ? NULL_KEY : key);
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entry = new HashMapEntry(oRealKey, value);
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hashIndex = hash(oRealKey);
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list = buckets[hashIndex];
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if (list == null)
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{
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list = new Bucket();
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buckets[hashIndex] = list;
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}
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oResult = list.add(entry);
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if (oResult == null)
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{
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modCount++;
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if (size++ == threshold)
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rehash();
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return null;
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}
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else
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{
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// SEH: if key already exists, we don't rehash & we don't update the modCount
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// because it is not a "structural" modification
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return oResult;
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}
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}
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/**
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* a private method, called by all of the constructors to initialize a new HashMap
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*
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* @param initialCapacity the initial capacity of this HashMap (>=0)
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* @param initialLoadFactor the load factor of this HashMap
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* (a misnomer, really, since the load factor of
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* a HashMap does not change)
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*/
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private void init(int initialCapacity, float initialLoadFactor)
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{
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size = 0;
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modCount = 0;
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capacity = initialCapacity;
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loadFactor = initialLoadFactor;
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threshold = (int) ((float) capacity * loadFactor);
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buckets = new Bucket[capacity];
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}
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/** private -- simply hashes a non-null Object to its array index */
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private int hash(Object key)
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{
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return Math.abs(key.hashCode() % capacity);
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}
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/**
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* increases the size of the HashMap and rehashes all keys to new array indices;
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* this is called when the addition of a new value would cause size() > threshold
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*/
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private void rehash()
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{
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int i;
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Bucket[] data = buckets;
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Bucket.Node node;
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modCount++;
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capacity = (capacity * 2) + 1;
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size = 0;
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threshold = (int) ((float) capacity * loadFactor);
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buckets = new Bucket[capacity];
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for (i = 0; i < data.length; i++)
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{
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if (data[i] != null)
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{
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node = data[i].first;
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while (node != null)
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{
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internalPut(node.getKey(), node.getValue());
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node = node.next;
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}
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}
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}
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}
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/**
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* a private method which does the "dirty work" (or some of it anyway) of fetching a value
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* with a key
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*
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* @param key the key for which to fetch an associated value
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*/
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private Map.Entry internalGet(Object key)
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{
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Bucket list;
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if (size == 0)
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{
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return null;
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}
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else
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{
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list = buckets[hash(((key == null) ? NULL_KEY : key))];
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return (list == null) ? null : list.getEntryByKey(key);
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}
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}
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/**
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* a private method used by inner class HashMapSet to implement its own
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* <pre>contains(Map.Entry)</pre> method; returns true if the supplied
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* key / value pair is found in this HashMap (again, using <pre>equals()</pre>,
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* rather than <pre>==</pre>)
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*
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* @param entry a Map.Entry to match against key / value pairs in
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* this HashMap
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*/
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private boolean containsEntry(Map.Entry entry)
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{
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Map.Entry oInternalEntry;
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if (entry == null)
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{
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return false;
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}
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else
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{
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oInternalEntry = internalGet(entry.getKey());
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return (oInternalEntry != null && oInternalEntry.equals(entry));
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}
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}
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/**
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* Serializes this object to the given stream.
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* @serialdata the <i>capacity</i>(int) that is the length of the
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* bucket array, the <i>size</i>(int) of the hash map are emitted
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* first. They are followed by size entries, each consisting of
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* a key (Object) and a value (Object).
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*/
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private void writeObject(ObjectOutputStream s)
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throws IOException
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{
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// the fields
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s.defaultWriteObject();
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s.writeInt(capacity);
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s.writeInt(size);
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Iterator it = entrySet().iterator();
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while (it.hasNext())
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{
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Map.Entry oEntry = (Map.Entry) it.next();
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s.writeObject(oEntry.getKey());
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s.writeObject(oEntry.getValue());
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}
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}
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/**
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* Deserializes this object from the given stream.
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* @serialdata the <i>capacity</i>(int) that is the length of the
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* bucket array, the <i>size</i>(int) of the hash map are emitted
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* first. They are followed by size entries, each consisting of
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* a key (Object) and a value (Object).
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*/
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private void readObject(ObjectInputStream s)
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throws IOException, ClassNotFoundException
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{
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// the fields
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s.defaultReadObject();
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capacity = s.readInt();
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int iLen = s.readInt();
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size = 0;
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modCount = 0;
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buckets = new Bucket[capacity];
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for (int i = 0; i < iLen; i++)
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{
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Object oKey = s.readObject();
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Object oValue = s.readObject();
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internalPut(oKey, oValue);
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}
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}
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// INNER CLASSES -------------------------------------------------------------
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// ---------------------------------------------------------------------------
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/**
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* an inner class providing a Set view of a HashMap; this implementation is
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* parameterized to view either a Set of keys or a Set of Map.Entry objects
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*
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* Note: a lot of these methods are implemented by AbstractSet, and would work
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* just fine without any meddling, but far greater efficiency can be gained by
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* overriding a number of them. And so I did.
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*
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* @author Jon Zeppieri
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* @version $Revision: 1.6 $
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* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
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*/
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private class HashMapSet extends AbstractSet
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implements Set
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{
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/** the type of this Set view: KEYS or ENTRIES */
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private int setType;
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/** construct a new HashtableSet with the supplied view type */
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HashMapSet(int type)
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{
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setType = type;
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}
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/**
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* adding an element is unsupported; this method simply throws an exception
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*
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* @throws UnsupportedOperationException
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*/
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public boolean add(Object o) throws UnsupportedOperationException
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{
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throw new UnsupportedOperationException();
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}
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/**
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* adding an element is unsupported; this method simply throws an exception
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*
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* @throws UnsupportedOperationException
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*/
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public boolean addAll(Collection c) throws UnsupportedOperationException
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{
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throw new UnsupportedOperationException();
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}
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/**
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* clears the backing HashMap; this is a prime example of an overridden implementation
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* which is far more efficient than its superclass implementation (which uses an iterator
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* and is O(n) -- this is an O(1) call)
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*/
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public void clear()
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{
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HashMap.this.clear();
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|
}
|
|
|
|
/**
|
|
* returns true if the supplied object is contained by this Set
|
|
*
|
|
* @param o an Object being testing to see if it is in this Set
|
|
*/
|
|
public boolean contains(Object o)
|
|
{
|
|
if (setType == KEYS)
|
|
return HashMap.this.containsKey(o);
|
|
else
|
|
return (o instanceof Map.Entry) ? HashMap.this.containsEntry((Map.Entry) o) : false;
|
|
}
|
|
|
|
/**
|
|
* returns true if the backing HashMap is empty (which is the only case either a KEYS
|
|
* Set or an ENTRIES Set would be empty)
|
|
*/
|
|
public boolean isEmpty()
|
|
{
|
|
return HashMap.this.isEmpty();
|
|
}
|
|
|
|
/**
|
|
* removes the supplied Object from the Set
|
|
*
|
|
* @param o the Object to be removed
|
|
*/
|
|
public boolean remove(Object o)
|
|
{
|
|
if (setType == KEYS)
|
|
return (HashMap.this.remove(o) != null);
|
|
else
|
|
return (o instanceof Map.Entry) ?
|
|
(HashMap.this.remove(((Map.Entry) o).getKey()) != null) : false;
|
|
}
|
|
|
|
/** returns the size of this Set (always equal to the size of the backing Hashtable) */
|
|
public int size()
|
|
{
|
|
return HashMap.this.size();
|
|
}
|
|
|
|
/** returns an Iterator over the elements of this Set */
|
|
public Iterator iterator()
|
|
{
|
|
return new HashMapIterator(setType);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Like the above Set view, except this one if for values, which are not
|
|
* guaranteed to be unique in a Map; this prvides a Bag of values
|
|
* in the HashMap
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
private class HashMapCollection extends AbstractCollection
|
|
implements Collection
|
|
{
|
|
/** a trivial contructor for HashMapCollection */
|
|
HashMapCollection()
|
|
{
|
|
}
|
|
|
|
/**
|
|
* adding elements is not supported by this Collection;
|
|
* this method merely throws an exception
|
|
*
|
|
* @throws UnsupportedOperationException
|
|
*/
|
|
public boolean add(Object o) throws UnsupportedOperationException
|
|
{
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* adding elements is not supported by this Collection;
|
|
* this method merely throws an exception
|
|
*
|
|
* @throws UnsupportedOperationException
|
|
*/
|
|
public boolean addAll(Collection c) throws UnsupportedOperationException
|
|
{
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/** removes all elements from this Collection (and from the backing HashMap) */
|
|
public void clear()
|
|
{
|
|
HashMap.this.clear();
|
|
}
|
|
|
|
/**
|
|
* returns true if this Collection contains at least one Object which equals() the
|
|
* supplied Object
|
|
*
|
|
* @param o the Object to compare against those in the Set
|
|
*/
|
|
public boolean contains(Object o)
|
|
{
|
|
return HashMap.this.containsValue(o);
|
|
}
|
|
|
|
/** returns true IFF the Collection has no elements */
|
|
public boolean isEmpty()
|
|
{
|
|
return HashMap.this.isEmpty();
|
|
}
|
|
|
|
/** returns the size of this Collection */
|
|
public int size()
|
|
{
|
|
return HashMap.this.size();
|
|
}
|
|
|
|
/** returns an Iterator over the elements in this Collection */
|
|
public Iterator iterator()
|
|
{
|
|
return new HashMapIterator(VALUES);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a class which implements the Iterator interface and is used for
|
|
* iterating over HashMaps;
|
|
* this implementation is parameterized to give a sequential view of
|
|
* keys, values, or entries; it also allows the removal of elements,
|
|
* as per the Javasoft spec.
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
class HashMapIterator implements Iterator
|
|
{
|
|
/** the type of this Iterator: KEYS, VALUES, or ENTRIES */
|
|
private int myType;
|
|
/**
|
|
* the number of modifications to the backing Hashtable for which
|
|
* this Iterator can account (idea ripped off from Stuart Ballard)
|
|
*/
|
|
private int knownMods;
|
|
/** the location of our sequential "cursor" */
|
|
private int position;
|
|
/** the current index of the BucketList array */
|
|
private int bucketIndex;
|
|
/** a reference, originally null, to the specific Bucket our "cursor" is pointing to */
|
|
private Bucket.Node currentNode;
|
|
/** a reference to the current key -- used fro removing elements via the Iterator */
|
|
private Object currentKey;
|
|
|
|
/** construct a new HashtableIterator with the supllied type: KEYS, VALUES, or ENTRIES */
|
|
HashMapIterator(int type)
|
|
{
|
|
myType = type;
|
|
knownMods = HashMap.this.modCount;
|
|
position = 0;
|
|
bucketIndex = -1;
|
|
currentNode = null;
|
|
currentKey = null;
|
|
}
|
|
|
|
/**
|
|
* Stuart Ballard's code: if the backing HashMap has been altered through anything
|
|
* but <i>this</i> Iterator's <pre>remove()</pre> method, we will give up right here,
|
|
* rather than risking undefined behavior
|
|
*
|
|
* @throws ConcurrentModificationException
|
|
*/
|
|
private void checkMod()
|
|
{
|
|
if (knownMods != HashMap.this.modCount)
|
|
throw new ConcurrentModificationException();
|
|
}
|
|
|
|
/** returns true if the Iterator has more elements */
|
|
public boolean hasNext()
|
|
{
|
|
checkMod();
|
|
return position < HashMap.this.size();
|
|
}
|
|
|
|
/** returns the next element in the Iterator's sequential view */
|
|
public Object next()
|
|
{
|
|
Bucket list = null;
|
|
Object result;
|
|
checkMod();
|
|
try
|
|
{
|
|
while (currentNode == null)
|
|
{
|
|
while (list == null)
|
|
list = HashMap.this.buckets[++bucketIndex];
|
|
currentNode = list.first;
|
|
}
|
|
currentKey = currentNode.getKey();
|
|
result = (myType == KEYS) ? currentKey :
|
|
((myType == VALUES) ? currentNode.getValue() : currentNode);
|
|
currentNode = currentNode.next;
|
|
}
|
|
catch(Exception e)
|
|
{
|
|
throw new NoSuchElementException();
|
|
}
|
|
position++;
|
|
return result;
|
|
}
|
|
|
|
/**
|
|
* removes from the backing HashMap the last element which was fetched with the
|
|
* <pre>next()</pre> method
|
|
*/
|
|
public void remove()
|
|
{
|
|
checkMod();
|
|
if (currentKey == null)
|
|
{
|
|
throw new IllegalStateException();
|
|
}
|
|
else
|
|
{
|
|
HashMap.this.remove(currentKey);
|
|
knownMods++;
|
|
position--;
|
|
currentKey = null;
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a singleton instance of this class (HashMap.NULL_KEY)
|
|
* is used to represent the null key in HashMap objects
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
private static class Null
|
|
{
|
|
/** trivial constructor */
|
|
Null()
|
|
{
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a HashMap version of Map.Entry -- one thing in this implementation is
|
|
* HashMap-specific: if the key is HashMap.NULL_KEY, getKey() will return
|
|
* null
|
|
*
|
|
* Simply, a key / value pair
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
private static class HashMapEntry extends Bucket.Node implements Map.Entry
|
|
{
|
|
/** construct a new HashMapEntry with the given key and value */
|
|
public HashMapEntry(Object key, Object value)
|
|
{
|
|
super(key, value);
|
|
}
|
|
|
|
/**
|
|
* if the key == HashMap.NULL_KEY, null is returned, otherwise the actual
|
|
* key is returned
|
|
*/
|
|
public Object getKey()
|
|
{
|
|
Object oResult = super.getKey();
|
|
return (oResult == HashMap.NULL_KEY) ? null : oResult;
|
|
}
|
|
}
|
|
// EOF -----------------------------------------------------------------------
|
|
}
|