1 /*
   2  * Copyright (c) 1999, 2004, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 /*
  27  * Licensed Materials - Property of IBM
  28  * RMI-IIOP v1.0
  29  * Copyright IBM Corp. 1998 1999  All Rights Reserved
  30  *
  31  */
  32 
  33 package com.sun.corba.se.impl.util;
  34 
  35 import java.util.Dictionary;
  36 import java.util.Enumeration;
  37 import java.util.NoSuchElementException;
  38 
  39 /**
  40  * IdentityHashtable is a modified copy of the 1.1.6 Hashtable class which
  41  * does not rely on the hashCode() and equals() methods of the key or value;
  42  * instead, it uses the System.identityHashcode() method and pointer comparison.
  43  * In addition, all synchronization has been removed.
  44  */
  45 public final class IdentityHashtable extends Dictionary {
  46     /**
  47      * The hash table data.
  48      */
  49     private transient IdentityHashtableEntry table[];
  50 
  51     /**
  52      * The total number of entries in the hash table.
  53      */
  54     private transient int count;
  55 
  56     /**
  57      * Rehashes the table when count exceeds this threshold.
  58      */
  59     private int threshold;
  60 
  61     /**
  62      * The load factor for the hashtable.
  63      */
  64     private float loadFactor;
  65 
  66     /**
  67      * Constructs a new, empty hashtable with the specified initial
  68      * capacity and the specified load factor.
  69      *
  70      * @param      initialCapacity   the initial capacity of the hashtable.
  71      * @param      loadFactor        a number between 0.0 and 1.0.
  72      * @exception  IllegalArgumentException  if the initial capacity is less
  73      *               than or equal to zero, or if the load factor is less than
  74      *               or equal to zero.
  75      * @since      JDK1.0
  76      */
  77     public IdentityHashtable(int initialCapacity, float loadFactor) {
  78         if ((initialCapacity <= 0) || (loadFactor <= 0.0)) {
  79             throw new IllegalArgumentException();
  80         }
  81         this.loadFactor = loadFactor;
  82         table = new IdentityHashtableEntry[initialCapacity];
  83         threshold = (int)(initialCapacity * loadFactor);
  84     }
  85 
  86     /**
  87      * Constructs a new, empty hashtable with the specified initial capacity
  88      * and default load factor.
  89      *
  90      * @param   initialCapacity   the initial capacity of the hashtable.
  91      * @since   JDK1.0
  92      */
  93     public IdentityHashtable(int initialCapacity) {
  94         this(initialCapacity, 0.75f);
  95     }
  96 
  97     /**
  98      * Constructs a new, empty hashtable with a default capacity and load
  99      * factor.
 100      *
 101      * @since   JDK1.0
 102      */
 103     public IdentityHashtable() {
 104         this(101, 0.75f);
 105     }
 106 
 107     /**
 108      * Returns the number of keys in this hashtable.
 109      *
 110      * @return  the number of keys in this hashtable.
 111      * @since   JDK1.0
 112      */
 113     public int size() {
 114         return count;
 115     }
 116 
 117     /**
 118      * Tests if this hashtable maps no keys to values.
 119      *
 120      * @return  <code>true</code> if this hashtable maps no keys to values;
 121      *          <code>false</code> otherwise.
 122      * @since   JDK1.0
 123      */
 124     public boolean isEmpty() {
 125         return count == 0;
 126     }
 127 
 128     /**
 129      * Returns an enumeration of the keys in this hashtable.
 130      *
 131      * @return  an enumeration of the keys in this hashtable.
 132      * @see     java.util.Enumeration
 133      * @see     java.util.Hashtable#elements()
 134      * @since   JDK1.0
 135      */
 136     public Enumeration keys() {
 137         return new IdentityHashtableEnumerator(table, true);
 138     }
 139 
 140     /**
 141      * Returns an enumeration of the values in this hashtable.
 142      * Use the Enumeration methods on the returned object to fetch the elements
 143      * sequentially.
 144      *
 145      * @return  an enumeration of the values in this hashtable.
 146      * @see     java.util.Enumeration
 147      * @see     java.util.Hashtable#keys()
 148      * @since   JDK1.0
 149      */
 150     public Enumeration elements() {
 151         return new IdentityHashtableEnumerator(table, false);
 152     }
 153 
 154     /**
 155      * Tests if some key maps into the specified value in this hashtable.
 156      * This operation is more expensive than the <code>containsKey</code>
 157      * method.
 158      *
 159      * @param      value   a value to search for.
 160      * @return     <code>true</code> if some key maps to the
 161      *             <code>value</code> argument in this hashtable;
 162      *             <code>false</code> otherwise.
 163      * @exception  NullPointerException  if the value is <code>null</code>.
 164      * @see        java.util.Hashtable#containsKey(java.lang.Object)
 165      * @since      JDK1.0
 166      */
 167     public boolean contains(Object value) {
 168         if (value == null) {
 169             throw new NullPointerException();
 170         }
 171 
 172         IdentityHashtableEntry tab[] = table;
 173         for (int i = tab.length ; i-- > 0 ;) {
 174             for (IdentityHashtableEntry e = tab[i] ; e != null ; e = e.next) {
 175                 if (e.value == value) {
 176                     return true;
 177                 }
 178             }
 179         }
 180         return false;
 181     }
 182 
 183     /**
 184      * Tests if the specified object is a key in this hashtable.
 185      *
 186      * @param   key   possible key.
 187      * @return  <code>true</code> if the specified object is a key in this
 188      *          hashtable; <code>false</code> otherwise.
 189      * @see     java.util.Hashtable#contains(java.lang.Object)
 190      * @since   JDK1.0
 191      */
 192     public boolean containsKey(Object key) {
 193         IdentityHashtableEntry tab[] = table;
 194         int hash = System.identityHashCode(key);
 195         int index = (hash & 0x7FFFFFFF) % tab.length;
 196         for (IdentityHashtableEntry e = tab[index] ; e != null ; e = e.next) {
 197             if ((e.hash == hash) && e.key == key) {
 198                 return true;
 199             }
 200         }
 201         return false;
 202     }
 203 
 204     /**
 205      * Returns the value to which the specified key is mapped in this hashtable.
 206      *
 207      * @param   key   a key in the hashtable.
 208      * @return  the value to which the key is mapped in this hashtable;
 209      *          <code>null</code> if the key is not mapped to any value in
 210      *          this hashtable.
 211      * @see     java.util.Hashtable#put(java.lang.Object, java.lang.Object)
 212      * @since   JDK1.0
 213      */
 214     public Object get(Object key) {
 215         IdentityHashtableEntry tab[] = table;
 216         int hash = System.identityHashCode(key);
 217         int index = (hash & 0x7FFFFFFF) % tab.length;
 218         for (IdentityHashtableEntry e = tab[index] ; e != null ; e = e.next) {
 219             if ((e.hash == hash) && e.key == key) {
 220                 return e.value;
 221             }
 222         }
 223         return null;
 224     }
 225 
 226     /**
 227      * Rehashes the contents of the hashtable into a hashtable with a
 228      * larger capacity. This method is called automatically when the
 229      * number of keys in the hashtable exceeds this hashtable's capacity
 230      * and load factor.
 231      *
 232      * @since   JDK1.0
 233      */
 234     protected void rehash() {
 235         int oldCapacity = table.length;
 236         IdentityHashtableEntry oldTable[] = table;
 237 
 238         int newCapacity = oldCapacity * 2 + 1;
 239         IdentityHashtableEntry newTable[] = new IdentityHashtableEntry[newCapacity];
 240 
 241         threshold = (int)(newCapacity * loadFactor);
 242         table = newTable;
 243 
 244         //System.out.println("rehash old=" + oldCapacity + ", new=" + newCapacity + ", thresh=" + threshold + ", count=" + count);
 245 
 246         for (int i = oldCapacity ; i-- > 0 ;) {
 247             for (IdentityHashtableEntry old = oldTable[i] ; old != null ; ) {
 248                 IdentityHashtableEntry e = old;
 249                 old = old.next;
 250 
 251                 int index = (e.hash & 0x7FFFFFFF) % newCapacity;
 252                 e.next = newTable[index];
 253                 newTable[index] = e;
 254             }
 255         }
 256     }
 257 
 258     /**
 259      * Maps the specified <code>key</code> to the specified
 260      * <code>value</code> in this hashtable. Neither the key nor the
 261      * value can be <code>null</code>.
 262      * <p>
 263      * The value can be retrieved by calling the <code>get</code> method
 264      * with a key that is equal to the original key.
 265      *
 266      * @param      key     the hashtable key.
 267      * @param      value   the value.
 268      * @return     the previous value of the specified key in this hashtable,
 269      *             or <code>null</code> if it did not have one.
 270      * @exception  NullPointerException  if the key or value is
 271      *               <code>null</code>.
 272      * @see     java.util.Hashtable#get(java.lang.Object)
 273      * @since   JDK1.0
 274      */
 275     public Object put(Object key, Object value) {
 276         // Make sure the value is not null
 277         if (value == null) {
 278             throw new NullPointerException();
 279         }
 280 
 281         // Makes sure the key is not already in the hashtable.
 282         IdentityHashtableEntry tab[] = table;
 283         int hash = System.identityHashCode(key);
 284         int index = (hash & 0x7FFFFFFF) % tab.length;
 285         for (IdentityHashtableEntry e = tab[index] ; e != null ; e = e.next) {
 286             if ((e.hash == hash) && e.key == key) {
 287                 Object old = e.value;
 288                 e.value = value;
 289                 return old;
 290             }
 291         }
 292 
 293         if (count >= threshold) {
 294             // Rehash the table if the threshold is exceeded
 295             rehash();
 296             return put(key, value);
 297         }
 298 
 299         // Creates the new entry.
 300         IdentityHashtableEntry e = new IdentityHashtableEntry();
 301         e.hash = hash;
 302         e.key = key;
 303         e.value = value;
 304         e.next = tab[index];
 305         tab[index] = e;
 306         count++;
 307         return null;
 308     }
 309 
 310         /**
 311      * Removes the key (and its corresponding value) from this
 312      * hashtable. This method does nothing if the key is not in the hashtable.
 313      *
 314      * @param   key   the key that needs to be removed.
 315      * @return  the value to which the key had been mapped in this hashtable,
 316      *          or <code>null</code> if the key did not have a mapping.
 317      * @since   JDK1.0
 318      */
 319     public Object remove(Object key) {
 320         IdentityHashtableEntry tab[] = table;
 321         int hash = System.identityHashCode(key);
 322         int index = (hash & 0x7FFFFFFF) % tab.length;
 323         for (IdentityHashtableEntry e = tab[index], prev = null ; e != null ; prev = e, e = e.next) {
 324             if ((e.hash == hash) && e.key == key) {
 325                 if (prev != null) {
 326                     prev.next = e.next;
 327                 } else {
 328                     tab[index] = e.next;
 329                 }
 330                 count--;
 331                 return e.value;
 332             }
 333         }
 334         return null;
 335     }
 336 
 337     /**
 338      * Clears this hashtable so that it contains no keys.
 339      *
 340      * @since   JDK1.0
 341      */
 342     public void clear() {
 343         IdentityHashtableEntry tab[] = table;
 344         for (int index = tab.length; --index >= 0; )
 345             tab[index] = null;
 346         count = 0;
 347     }
 348 
 349     /**
 350      * Returns a rather long string representation of this hashtable.
 351      *
 352      * @return  a string representation of this hashtable.
 353      * @since   JDK1.0
 354      */
 355     public String toString() {
 356         int max = size() - 1;
 357         StringBuffer buf = new StringBuffer();
 358         Enumeration k = keys();
 359         Enumeration e = elements();
 360         buf.append("{");
 361 
 362         for (int i = 0; i <= max; i++) {
 363             String s1 = k.nextElement().toString();
 364             String s2 = e.nextElement().toString();
 365             buf.append(s1 + "=" + s2);
 366             if (i < max) {
 367                 buf.append(", ");
 368             }
 369         }
 370         buf.append("}");
 371         return buf.toString();
 372     }
 373 }