001/* AbstractMap.java -- Abstract implementation of most of Map
002   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2005
003   Free Software Foundation, Inc.
004
005This file is part of GNU Classpath.
006
007GNU Classpath is free software; you can redistribute it and/or modify
008it under the terms of the GNU General Public License as published by
009the Free Software Foundation; either version 2, or (at your option)
010any later version.
011
012GNU Classpath is distributed in the hope that it will be useful, but
013WITHOUT ANY WARRANTY; without even the implied warranty of
014MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015General Public License for more details.
016
017You should have received a copy of the GNU General Public License
018along with GNU Classpath; see the file COPYING.  If not, write to the
019Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02002110-1301 USA.
021
022Linking this library statically or dynamically with other modules is
023making a combined work based on this library.  Thus, the terms and
024conditions of the GNU General Public License cover the whole
025combination.
026
027As a special exception, the copyright holders of this library give you
028permission to link this library with independent modules to produce an
029executable, regardless of the license terms of these independent
030modules, and to copy and distribute the resulting executable under
031terms of your choice, provided that you also meet, for each linked
032independent module, the terms and conditions of the license of that
033module.  An independent module is a module which is not derived from
034or based on this library.  If you modify this library, you may extend
035this exception to your version of the library, but you are not
036obligated to do so.  If you do not wish to do so, delete this
037exception statement from your version. */
038
039
040package java.util;
041
042import gnu.java.lang.CPStringBuilder;
043
044import java.io.Serializable;
045
046/**
047 * An abstract implementation of Map to make it easier to create your own
048 * implementations. In order to create an unmodifiable Map, subclass
049 * AbstractMap and implement the <code>entrySet</code> (usually via an
050 * AbstractSet).  To make it modifiable, also implement <code>put</code>,
051 * and have <code>entrySet().iterator()</code> support <code>remove</code>.
052 * <p>
053 *
054 * It is recommended that classes which extend this support at least the
055 * no-argument constructor, and a constructor which accepts another Map.
056 * Further methods in this class may be overridden if you have a more
057 * efficient implementation.
058 *
059 * @author Original author unknown
060 * @author Bryce McKinlay
061 * @author Eric Blake (ebb9@email.byu.edu)
062 * @see Map
063 * @see Collection
064 * @see HashMap
065 * @see LinkedHashMap
066 * @see TreeMap
067 * @see WeakHashMap
068 * @see IdentityHashMap
069 * @since 1.2
070 * @status updated to 1.4
071 */
072public abstract class AbstractMap<K, V> implements Map<K, V>
073{
074  /**
075   * A class containing an immutable key and value.  The
076   * implementation of {@link Entry#setValue(V)} for this class
077   * simply throws an {@link UnsupportedOperationException},
078   * thus preventing changes being made.  This is useful when
079   * a static thread-safe view of a map is required.
080   *
081   * @since 1.6
082   */
083  public static class SimpleImmutableEntry<K, V>
084    implements Entry<K, V>, Serializable
085  {
086    /**
087     * Compatible with JDK 1.6
088     */
089    private static final long serialVersionUID = 7138329143949025153L;
090
091    K key;
092    V value;
093
094    public SimpleImmutableEntry(K key, V value)
095    {
096      this.key = key;
097      this.value = value;
098    }
099
100    public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry)
101    {
102      this(entry.getKey(), entry.getValue());
103    }
104
105    public K getKey()
106    {
107      return key;
108    }
109
110    public V getValue()
111    {
112      return value;
113    }
114
115    public V setValue(V value)
116    {
117      throw new UnsupportedOperationException("setValue not supported on immutable entry");
118    }
119  }
120
121/** An "enum" of iterator types. */
122  // Package visible for use by subclasses.
123  static final int KEYS = 0,
124                   VALUES = 1,
125                   ENTRIES = 2;
126
127  /**
128   * The cache for {@link #keySet()}.
129   */
130  // Package visible for use by subclasses.
131  Set<K> keys;
132
133  /**
134   * The cache for {@link #values()}.
135   */
136  // Package visible for use by subclasses.
137  Collection<V> values;
138
139  /**
140   * The main constructor, for use by subclasses.
141   */
142  protected AbstractMap()
143  {
144  }
145
146  /**
147   * Returns a set view of the mappings in this Map.  Each element in the
148   * set must be an implementation of Map.Entry.  The set is backed by
149   * the map, so that changes in one show up in the other.  Modifications
150   * made while an iterator is in progress cause undefined behavior.  If
151   * the set supports removal, these methods must be valid:
152   * <code>Iterator.remove</code>, <code>Set.remove</code>,
153   * <code>removeAll</code>, <code>retainAll</code>, and <code>clear</code>.
154   * Element addition is not supported via this set.
155   *
156   * @return the entry set
157   * @see Map.Entry
158   */
159  public abstract Set<Map.Entry<K, V>> entrySet();
160
161  /**
162   * Remove all entries from this Map (optional operation). This default
163   * implementation calls entrySet().clear(). NOTE: If the entry set does
164   * not permit clearing, then this will fail, too. Subclasses often
165   * override this for efficiency.  Your implementation of entrySet() should
166   * not call <code>AbstractMap.clear</code> unless you want an infinite loop.
167   *
168   * @throws UnsupportedOperationException if <code>entrySet().clear()</code>
169   *         does not support clearing.
170   * @see Set#clear()
171   */
172  public void clear()
173  {
174    entrySet().clear();
175  }
176
177  /**
178   * Create a shallow copy of this Map, no keys or values are copied. The
179   * default implementation simply calls <code>super.clone()</code>.
180   *
181   * @return the shallow clone
182   * @throws CloneNotSupportedException if a subclass is not Cloneable
183   * @see Cloneable
184   * @see Object#clone()
185   */
186  protected Object clone() throws CloneNotSupportedException
187  {
188    AbstractMap<K, V> copy = (AbstractMap<K, V>) super.clone();
189    // Clear out the caches; they are stale.
190    copy.keys = null;
191    copy.values = null;
192    return copy;
193  }
194
195  /**
196   * Returns true if this contains a mapping for the given key. This
197   * implementation does a linear search, O(n), over the
198   * <code>entrySet()</code>, returning <code>true</code> if a match
199   * is found, <code>false</code> if the iteration ends. Many subclasses
200   * can implement this more efficiently.
201   *
202   * @param key the key to search for
203   * @return true if the map contains the key
204   * @throws NullPointerException if key is <code>null</code> but the map
205   *         does not permit null keys
206   * @see #containsValue(Object)
207   */
208  public boolean containsKey(Object key)
209  {
210    Iterator<Map.Entry<K, V>> entries = entrySet().iterator();
211    int pos = size();
212    while (--pos >= 0)
213      if (equals(key, entries.next().getKey()))
214        return true;
215    return false;
216  }
217
218  /**
219   * Returns true if this contains at least one mapping with the given value.
220   * This implementation does a linear search, O(n), over the
221   * <code>entrySet()</code>, returning <code>true</code> if a match
222   * is found, <code>false</code> if the iteration ends. A match is
223   * defined as a value, v, where <code>(value == null ? v == null :
224   * value.equals(v))</code>.  Subclasses are unlikely to implement
225   * this more efficiently.
226   *
227   * @param value the value to search for
228   * @return true if the map contains the value
229   * @see #containsKey(Object)
230   */
231  public boolean containsValue(Object value)
232  {
233    Iterator<Map.Entry<K, V>> entries = entrySet().iterator();
234    int pos = size();
235    while (--pos >= 0)
236      if (equals(value, entries.next().getValue()))
237        return true;
238    return false;
239  }
240
241  /**
242   * Compares the specified object with this map for equality. Returns
243   * <code>true</code> if the other object is a Map with the same mappings,
244   * that is,<br>
245   * <code>o instanceof Map && entrySet().equals(((Map) o).entrySet();</code>
246   *
247   * @param o the object to be compared
248   * @return true if the object equals this map
249   * @see Set#equals(Object)
250   */
251  public boolean equals(Object o)
252  {
253    return (o == this
254            || (o instanceof Map
255                && entrySet().equals(((Map<K, V>) o).entrySet())));
256  }
257
258  /**
259   * Returns the value mapped by the given key. Returns <code>null</code> if
260   * there is no mapping.  However, in Maps that accept null values, you
261   * must rely on <code>containsKey</code> to determine if a mapping exists.
262   * This iteration takes linear time, searching entrySet().iterator() of
263   * the key.  Many implementations override this method.
264   *
265   * @param key the key to look up
266   * @return the value associated with the key, or null if key not in map
267   * @throws NullPointerException if this map does not accept null keys
268   * @see #containsKey(Object)
269   */
270  public V get(Object key)
271  {
272    Iterator<Map.Entry<K, V>> entries = entrySet().iterator();
273    int pos = size();
274    while (--pos >= 0)
275      {
276        Map.Entry<K, V> entry = entries.next();
277        if (equals(key, entry.getKey()))
278          return entry.getValue();
279      }
280    return null;
281  }
282
283  /**
284   * Returns the hash code for this map. As defined in Map, this is the sum
285   * of all hashcodes for each Map.Entry object in entrySet, or basically
286   * entrySet().hashCode().
287   *
288   * @return the hash code
289   * @see Map.Entry#hashCode()
290   * @see Set#hashCode()
291   */
292  public int hashCode()
293  {
294    return entrySet().hashCode();
295  }
296
297  /**
298   * Returns true if the map contains no mappings. This is implemented by
299   * <code>size() == 0</code>.
300   *
301   * @return true if the map is empty
302   * @see #size()
303   */
304  public boolean isEmpty()
305  {
306    return size() == 0;
307  }
308
309  /**
310   * Returns a set view of this map's keys. The set is backed by the map,
311   * so changes in one show up in the other. Modifications while an iteration
312   * is in progress produce undefined behavior. The set supports removal
313   * if entrySet() does, but does not support element addition.
314   * <p>
315   *
316   * This implementation creates an AbstractSet, where the iterator wraps
317   * the entrySet iterator, size defers to the Map's size, and contains
318   * defers to the Map's containsKey. The set is created on first use, and
319   * returned on subsequent uses, although since no synchronization occurs,
320   * there is a slight possibility of creating two sets.
321   *
322   * @return a Set view of the keys
323   * @see Set#iterator()
324   * @see #size()
325   * @see #containsKey(Object)
326   * @see #values()
327   */
328  public Set<K> keySet()
329  {
330    if (keys == null)
331      keys = new AbstractSet<K>()
332      {
333        /**
334         * Retrieves the number of keys in the backing map.
335         *
336         * @return The number of keys.
337         */
338        public int size()
339        {
340          return AbstractMap.this.size();
341        }
342
343        /**
344         * Returns true if the backing map contains the
345         * supplied key.
346         *
347         * @param key The key to search for.
348         * @return True if the key was found, false otherwise.
349         */
350        public boolean contains(Object key)
351        {
352          return containsKey(key);
353        }
354
355        /**
356         * Returns an iterator which iterates over the keys
357         * in the backing map, using a wrapper around the
358         * iterator returned by <code>entrySet()</code>.
359         *
360         * @return An iterator over the keys.
361         */
362        public Iterator<K> iterator()
363        {
364          return new Iterator<K>()
365          {
366            /**
367             * The iterator returned by <code>entrySet()</code>.
368             */
369            private final Iterator<Map.Entry<K, V>> map_iterator
370              = entrySet().iterator();
371
372            /**
373             * Returns true if a call to <code>next()</code> will
374             * return another key.
375             *
376             * @return True if the iterator has not yet reached
377             *         the last key.
378             */
379            public boolean hasNext()
380            {
381              return map_iterator.hasNext();
382            }
383
384            /**
385             * Returns the key from the next entry retrieved
386             * by the underlying <code>entrySet()</code> iterator.
387             *
388             * @return The next key.
389             */
390           public K next()
391            {
392              return map_iterator.next().getKey();
393            }
394
395            /**
396             * Removes the map entry which has a key equal
397             * to that returned by the last call to
398             * <code>next()</code>.
399             *
400             * @throws UnsupportedOperationException if the
401             *         map doesn't support removal.
402             */
403            public void remove()
404            {
405              map_iterator.remove();
406            }
407          };
408        }
409      };
410    return keys;
411  }
412
413  /**
414   * Associates the given key to the given value (optional operation). If the
415   * map already contains the key, its value is replaced. This implementation
416   * simply throws an UnsupportedOperationException. Be aware that in a map
417   * that permits <code>null</code> values, a null return does not always
418   * imply that the mapping was created.
419   *
420   * @param key the key to map
421   * @param value the value to be mapped
422   * @return the previous value of the key, or null if there was no mapping
423   * @throws UnsupportedOperationException if the operation is not supported
424   * @throws ClassCastException if the key or value is of the wrong type
425   * @throws IllegalArgumentException if something about this key or value
426   *         prevents it from existing in this map
427   * @throws NullPointerException if the map forbids null keys or values
428   * @see #containsKey(Object)
429   */
430  public V put(K key, V value)
431  {
432    throw new UnsupportedOperationException();
433  }
434
435  /**
436   * Copies all entries of the given map to this one (optional operation). If
437   * the map already contains a key, its value is replaced. This implementation
438   * simply iterates over the map's entrySet(), calling <code>put</code>,
439   * so it is not supported if puts are not.
440   *
441   * @param m the mapping to load into this map
442   * @throws UnsupportedOperationException if the operation is not supported
443   *         by this map.
444   * @throws ClassCastException if a key or value is of the wrong type for
445   *         adding to this map.
446   * @throws IllegalArgumentException if something about a key or value
447   *         prevents it from existing in this map.
448   * @throws NullPointerException if the map forbids null keys or values.
449   * @throws NullPointerException if <code>m</code> is null.
450   * @see #put(Object, Object)
451   */
452  public void putAll(Map<? extends K, ? extends V> m)
453  {
454    // FIXME: bogus circumlocution.
455    Iterator entries2 = m.entrySet().iterator();
456    Iterator<Map.Entry<? extends K, ? extends V>> entries
457      = (Iterator<Map.Entry<? extends K, ? extends V>>) entries2;
458    int pos = m.size();
459    while (--pos >= 0)
460      {
461        Map.Entry<? extends K, ? extends V> entry = entries.next();
462        put(entry.getKey(), entry.getValue());
463      }
464  }
465
466  /**
467   * Removes the mapping for this key if present (optional operation). This
468   * implementation iterates over the entrySet searching for a matching
469   * key, at which point it calls the iterator's <code>remove</code> method.
470   * It returns the result of <code>getValue()</code> on the entry, if found,
471   * or null if no entry is found. Note that maps which permit null values
472   * may also return null if the key was removed.  If the entrySet does not
473   * support removal, this will also fail. This is O(n), so many
474   * implementations override it for efficiency.
475   *
476   * @param key the key to remove
477   * @return the value the key mapped to, or null if not present.
478   *         Null may also be returned if null values are allowed
479   *         in the map and the value of this mapping is null.
480   * @throws UnsupportedOperationException if deletion is unsupported
481   * @see Iterator#remove()
482   */
483  public V remove(Object key)
484  {
485    Iterator<Map.Entry<K, V>> entries = entrySet().iterator();
486    int pos = size();
487    while (--pos >= 0)
488      {
489        Map.Entry<K, V> entry = entries.next();
490        if (equals(key, entry.getKey()))
491          {
492            // Must get the value before we remove it from iterator.
493            V r = entry.getValue();
494            entries.remove();
495            return r;
496          }
497      }
498    return null;
499  }
500
501  /**
502   * Returns the number of key-value mappings in the map. If there are more
503   * than Integer.MAX_VALUE mappings, return Integer.MAX_VALUE. This is
504   * implemented as <code>entrySet().size()</code>.
505   *
506   * @return the number of mappings
507   * @see Set#size()
508   */
509  public int size()
510  {
511    return entrySet().size();
512  }
513
514  /**
515   * Returns a String representation of this map. This is a listing of the
516   * map entries (which are specified in Map.Entry as being
517   * <code>getKey() + "=" + getValue()</code>), separated by a comma and
518   * space (", "), and surrounded by braces ('{' and '}'). This implementation
519   * uses a StringBuffer and iterates over the entrySet to build the String.
520   * Note that this can fail with an exception if underlying keys or
521   * values complete abruptly in toString().
522   *
523   * @return a String representation
524   * @see Map.Entry#toString()
525   */
526  public String toString()
527  {
528    Iterator<Map.Entry<K, V>> entries = entrySet().iterator();
529    CPStringBuilder r = new CPStringBuilder("{");
530    for (int pos = size(); pos > 0; pos--)
531      {
532        Map.Entry<K, V> entry = entries.next();
533        r.append(entry.getKey());
534        r.append('=');
535        r.append(entry.getValue());
536        if (pos > 1)
537          r.append(", ");
538      }
539    r.append("}");
540    return r.toString();
541  }
542
543  /**
544   * Returns a collection or bag view of this map's values. The collection
545   * is backed by the map, so changes in one show up in the other.
546   * Modifications while an iteration is in progress produce undefined
547   * behavior. The collection supports removal if entrySet() does, but
548   * does not support element addition.
549   * <p>
550   *
551   * This implementation creates an AbstractCollection, where the iterator
552   * wraps the entrySet iterator, size defers to the Map's size, and contains
553   * defers to the Map's containsValue. The collection is created on first
554   * use, and returned on subsequent uses, although since no synchronization
555   * occurs, there is a slight possibility of creating two collections.
556   *
557   * @return a Collection view of the values
558   * @see Collection#iterator()
559   * @see #size()
560   * @see #containsValue(Object)
561   * @see #keySet()
562   */
563  public Collection<V> values()
564  {
565    if (values == null)
566      values = new AbstractCollection<V>()
567      {
568        /**
569         * Returns the number of values stored in
570         * the backing map.
571         *
572         * @return The number of values.
573         */
574       public int size()
575        {
576          return AbstractMap.this.size();
577        }
578
579        /**
580         * Returns true if the backing map contains
581         * the supplied value.
582         *
583         * @param value The value to search for.
584         * @return True if the value was found, false otherwise.
585         */
586        public boolean contains(Object value)
587        {
588          return containsValue(value);
589        }
590
591        /**
592         * Returns an iterator which iterates over the
593         * values in the backing map, by using a wrapper
594         * around the iterator returned by <code>entrySet()</code>.
595         *
596         * @return An iterator over the values.
597         */
598        public Iterator<V> iterator()
599        {
600          return new Iterator<V>()
601          {
602            /**
603             * The iterator returned by <code>entrySet()</code>.
604             */
605            private final Iterator<Map.Entry<K, V>> map_iterator
606              = entrySet().iterator();
607
608            /**
609             * Returns true if a call to <code>next()</call> will
610             * return another value.
611             *
612             * @return True if the iterator has not yet reached
613             * the last value.
614             */
615            public boolean hasNext()
616            {
617              return map_iterator.hasNext();
618            }
619
620            /**
621             * Returns the value from the next entry retrieved
622             * by the underlying <code>entrySet()</code> iterator.
623             *
624             * @return The next value.
625             */
626            public V next()
627            {
628              return map_iterator.next().getValue();
629            }
630
631            /**
632             * Removes the map entry which has a key equal
633             * to that returned by the last call to
634             * <code>next()</code>.
635             *
636             * @throws UnsupportedOperationException if the
637             *         map doesn't support removal.
638             */
639            public void remove()
640            {
641              map_iterator.remove();
642            }
643          };
644        }
645      };
646    return values;
647  }
648
649  /**
650   * Compare two objects according to Collection semantics.
651   *
652   * @param o1 the first object
653   * @param o2 the second object
654   * @return o1 == o2 || (o1 != null && o1.equals(o2))
655   */
656  // Package visible for use throughout java.util.
657  // It may be inlined since it is final.
658  static final boolean equals(Object o1, Object o2)
659  {
660    return o1 == o2 || (o1 != null && o1.equals(o2));
661  }
662
663  /**
664   * Hash an object according to Collection semantics.
665   *
666   * @param o the object to hash
667   * @return o1 == null ? 0 : o1.hashCode()
668   */
669  // Package visible for use throughout java.util.
670  // It may be inlined since it is final.
671  static final int hashCode(Object o)
672  {
673    return o == null ? 0 : o.hashCode();
674  }
675
676  /**
677   * A class which implements Map.Entry. It is shared by HashMap, TreeMap,
678   * Hashtable, and Collections. It is not specified by the JDK, but makes
679   * life much easier.
680   *
681   * @author Jon Zeppieri
682   * @author Eric Blake (ebb9@email.byu.edu)
683   *
684   * @since 1.6
685   */
686  public static class SimpleEntry<K, V> implements Entry<K, V>, Serializable
687  {
688
689    /**
690     * Compatible with JDK 1.6
691     */
692    private static final long serialVersionUID = -8499721149061103585L;
693
694    /**
695     * The key. Package visible for direct manipulation.
696     */
697    K key;
698
699    /**
700     * The value. Package visible for direct manipulation.
701     */
702    V value;
703
704    /**
705     * Basic constructor initializes the fields.
706     * @param newKey the key
707     * @param newValue the value
708     */
709    public SimpleEntry(K newKey, V newValue)
710    {
711      key = newKey;
712      value = newValue;
713    }
714
715    public SimpleEntry(Entry<? extends K, ? extends V> entry)
716    {
717      this(entry.getKey(), entry.getValue());
718    }
719
720    /**
721     * Compares the specified object with this entry. Returns true only if
722     * the object is a mapping of identical key and value. In other words,
723     * this must be:<br>
724     * <pre>(o instanceof Map.Entry)
725     *       && (getKey() == null ? ((HashMap) o).getKey() == null
726     *           : getKey().equals(((HashMap) o).getKey()))
727     *       && (getValue() == null ? ((HashMap) o).getValue() == null
728     *           : getValue().equals(((HashMap) o).getValue()))</pre>
729     *
730     * @param o the object to compare
731     * @return <code>true</code> if it is equal
732     */
733    public boolean equals(Object o)
734    {
735      if (! (o instanceof Map.Entry))
736        return false;
737      // Optimize for our own entries.
738      if (o instanceof SimpleEntry)
739        {
740          SimpleEntry e = (SimpleEntry) o;
741          return (AbstractMap.equals(key, e.key)
742                  && AbstractMap.equals(value, e.value));
743        }
744      Map.Entry e = (Map.Entry) o;
745      return (AbstractMap.equals(key, e.getKey())
746              && AbstractMap.equals(value, e.getValue()));
747    }
748
749    /**
750     * Get the key corresponding to this entry.
751     *
752     * @return the key
753     */
754    public K getKey()
755    {
756      return key;
757    }
758
759    /**
760     * Get the value corresponding to this entry. If you already called
761     * Iterator.remove(), the behavior undefined, but in this case it works.
762     *
763     * @return the value
764     */
765    public V getValue()
766    {
767      return value;
768    }
769
770    /**
771     * Returns the hash code of the entry.  This is defined as the exclusive-or
772     * of the hashcodes of the key and value (using 0 for null). In other
773     * words, this must be:<br>
774     * <pre>(getKey() == null ? 0 : getKey().hashCode())
775     *       ^ (getValue() == null ? 0 : getValue().hashCode())</pre>
776     *
777     * @return the hash code
778     */
779    public int hashCode()
780    {
781      return (AbstractMap.hashCode(key) ^ AbstractMap.hashCode(value));
782    }
783
784    /**
785     * Replaces the value with the specified object. This writes through
786     * to the map, unless you have already called Iterator.remove(). It
787     * may be overridden to restrict a null value.
788     *
789     * @param newVal the new value to store
790     * @return the old value
791     * @throws NullPointerException if the map forbids null values.
792     * @throws UnsupportedOperationException if the map doesn't support
793     *          <code>put()</code>.
794     * @throws ClassCastException if the value is of a type unsupported
795     *         by the map.
796     * @throws IllegalArgumentException if something else about this
797     *         value prevents it being stored in the map.
798     */
799    public V setValue(V newVal)
800    {
801      V r = value;
802      value = newVal;
803      return r;
804    }
805
806    /**
807     * This provides a string representation of the entry. It is of the form
808     * "key=value", where string concatenation is used on key and value.
809     *
810     * @return the string representation
811     */
812    public String toString()
813    {
814      return key + "=" + value;
815    }
816  } // class SimpleEntry
817
818
819}