collections.java

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        {
          return i.next();
        }
    }

    public boolean hasNext()
    {
      synchronized (mutex)
        {
          return i.hasNext();
        }
    }

    public void remove()
    {
      synchronized (mutex)
        {
          i.remove();
        }
    }
  } // class SynchronizedIterator

  /**
   * Returns a synchronized (thread-safe) list wrapper backed by the
   * given list. Notice that element access through the iterators
   * is thread-safe, but if the list can be structurally modified
   * (adding or removing elements) then you should synchronize around the
   * iteration to avoid non-deterministic behavior:<br>
   * <pre>
   * List l = Collections.synchronizedList(new List(...));
   * ...
   * synchronized (l)
   *   {
   *     Iterator i = l.iterator();
   *     while (i.hasNext())
   *       foo(i.next());
   *   }
   * </pre><p>
   *
   * The returned List implements Serializable, but can only be serialized if
   * the list it wraps is likewise Serializable. In addition, if the wrapped
   * list implements RandomAccess, this does too.
   *
   * @param l the list to wrap
   * @return a synchronized view of the list
   * @see Serializable
   * @see RandomAccess
   */
  public static List synchronizedList(List l)
  {
    if (l instanceof RandomAccess)
      return new SynchronizedRandomAccessList(l);
    return new SynchronizedList(l);
  }

  /**
   * The implementation of {@link #synchronizedList(List)} for sequential
   * lists. This class name is required for compatibility with Sun's JDK
   * serializability. Package visible, so that lists such as Vector.subList()
   * can specify which object to synchronize on.
   *
   * @author Eric Blake <[e-mail]>
   */
  static class SynchronizedList extends SynchronizedCollection
    implements List
  {
    /**
     * Compatible with JDK 1.4.
     */
    private static final long serialVersionUID = -7754090372962971524L;

    /**
     * The wrapped list; stored both here and in the superclass to avoid
     * excessive casting. Package visible for use by subclass.
     * @serial the wrapped list
     */
    final List list;

    /**
     * Wrap a given list.
     * @param l the list to wrap
     * @throws NullPointerException if l is null
     */
    SynchronizedList(List l)
    {
      super(l);
      list = l;
    }

    /**
     * Called only by trusted code to specify the mutex as well as the list.
     * @param sync the mutex
     * @param l the list
     */
    SynchronizedList(Object sync, List l)
    {
      super(sync, l);
      list = l;
    }

    public void add(int index, Object o)
    {
      synchronized (mutex)
        {
          list.add(index, o);
        }
    }

    public boolean addAll(int index, Collection c)
    {
      synchronized (mutex)
        {
          return list.addAll(index, c);
        }
    }

    public boolean equals(Object o)
    {
      synchronized (mutex)
        {
          return list.equals(o);
        }
    }

    public Object get(int index)
    {
      synchronized (mutex)
        {
          return list.get(index);
        }
    }

    public int hashCode()
    {
      synchronized (mutex)
        {
          return list.hashCode();
        }
    }

    public int indexOf(Object o)
    {
      synchronized (mutex)
        {
          return list.indexOf(o);
        }
    }

    public int lastIndexOf(Object o)
    {
      synchronized (mutex)
        {
          return list.lastIndexOf(o);
        }
    }

    public ListIterator listIterator()
    {
      synchronized (mutex)
        {
          return new SynchronizedListIterator(mutex, list.listIterator());
        }
    }

    public ListIterator listIterator(int index)
    {
      synchronized (mutex)
        {
          return new SynchronizedListIterator(mutex, list.listIterator(index));
        }
    }

    public Object remove(int index)
    {
      synchronized (mutex)
        {
          return list.remove(index);
        }
    }

    public Object set(int index, Object o)
    {
      synchronized (mutex)
        {
          return list.set(index, o);
        }
    }

    public List subList(int fromIndex, int toIndex)
    {
      synchronized (mutex)
        {
          return new SynchronizedList(mutex, list.subList(fromIndex, toIndex));
        }
    }
  } // class SynchronizedList

  /**
   * The implementation of {@link #synchronizedList(List)} for random-access
   * lists. This class name is required for compatibility with Sun's JDK
   * serializability.
   *
   * @author Eric Blake <[e-mail]>
   */
  private static final class SynchronizedRandomAccessList
    extends SynchronizedList implements RandomAccess
  {
    /**
     * Compatible with JDK 1.4.
     */
    private static final long serialVersionUID = 1530674583602358482L;

    /**
     * Wrap a given list.
     * @param l the list to wrap
     * @throws NullPointerException if l is null
     */
    SynchronizedRandomAccessList(List l)
    {
      super(l);
    }

    /**
     * Called only by trusted code to specify the mutex as well as the
     * collection.
     * @param sync the mutex
     * @param l the list
     */
    SynchronizedRandomAccessList(Object sync, List l)
    {
      super(sync, l);
    }

    public List subList(int fromIndex, int toIndex)
    {
      synchronized (mutex)
        {
          return new SynchronizedRandomAccessList(mutex,
                                                  list.subList(fromIndex,
                                                               toIndex));
        }
    }
  } // class SynchronizedRandomAccessList

  /**
   * The implementation of {@link SynchronizedList#listIterator()}. This
   * iterator must "sync" on the same object as the list it iterates over.
   *
   * @author Eric Blake <[e-mail]>
   */
  private static final class SynchronizedListIterator
    extends SynchronizedIterator implements ListIterator
  {
    /**
     * The wrapped iterator, stored both here and in the superclass to
     * avoid excessive casting.
     */
    private final ListIterator li;

    /**
     * Only trusted code creates a wrapper, with the specified sync.
     * @param sync the mutex
     * @param li the wrapped iterator
     */
    SynchronizedListIterator(Object sync, ListIterator li)
    {
      super(sync, li);
      this.li = li;
    }

    public void add(Object o)
    {
      synchronized (mutex)
        {
          li.add(o);
        }
    }
    public boolean hasPrevious()
    {
      synchronized (mutex)
        {
          return li.hasPrevious();
        }
    }

    public int nextIndex()
    {
      synchronized (mutex)
        {
          return li.nextIndex();
        }
    }

    public Object previous()
    {
      synchronized (mutex)
        {
          return li.previous();
        }
    }

    public int previousIndex()
    {
      synchronized (mutex)
        {
          return li.previousIndex();
        }
    }

    public void set(Object o)
    {
      synchronized (mutex)
        {
          li.set(o);
        }
    }
  } // class SynchronizedListIterator

  /**
   * Returns a synchronized (thread-safe) map wrapper backed by the given
   * map. Notice that element access through the collection views and their
   * iterators are thread-safe, but if the map can be structurally modified
   * (adding or removing elements) then you should synchronize around the
   * iteration to avoid non-deterministic behavior:<br>
   * <pre>
   * Map m = Collections.synchronizedMap(new Map(...));
   * ...
   * Set s = m.keySet(); // safe outside a synchronized block
   * synchronized (m) // synch on m, not s
   *   {
   *     Iterator i = s.iterator();
   *     while (i.hasNext())
   *       foo(i.next());
   *   }
   * </pre><p>
   *
   * The returned Map implements Serializable, but can only be serialized if
   * the map it wraps is likewise Serializable.
   *
   * @param m the map to wrap
   * @return a synchronized view of the map
   * @see Serializable
   */
  public static Map synchronizedMap(Map m)
  {
    return new SynchronizedMap(m);
  }

  /**
   * The implementation of {@link #synchronizedMap(Map)}. This
   * class name is required for compatibility with Sun's JDK serializability.
   *
   * @author Eric Blake <[e-mail]>
   */
  private static class SynchronizedMap implements Map, Serializable
  {
    /**
     * Compatible with JDK 1.4.
     */
    private static final long serialVersionUID = 1978198479659022715L;

    /**
     * The wrapped map.
     * @serial the real map
     */
    private final Map m;

    /**
     * The object to synchronize on.  When an instance is created via public
     * methods, it will be this; but other uses like
     * SynchronizedSortedMap.subMap() must specify another mutex. Package
     * visible for use by subclass.
     * @serial the lock
     */
    final Object mutex;

    /**
     * Cache the entry set.
     */
    private transient Set entries;

    /**
     * Cache the key set.
     */
    private transient Set keys;

    /**
     * Cache the value collection.
     */
    private transient Collection values;

    /**
     * Wrap a given map.
     * @param m the map to wrap
     * @throws NullPointerException if m is null
     */
    SynchronizedMap(Map m)
    {
      this.m = m;
      mutex = this;
      if (m == null)
        throw new NullPointerException();
    }

    /**
     * Called only by trusted code to specify the mutex as well as the map.
     * @param sync the mutex
     * @param m the map
     */
    SynchronizedMap(Object sync, Map m)
    {
      this.m = m;
      mutex = sync;
    }

    public void clear()
    {
      synchronized (mutex)
        {
          m.clear();
        }
    }

    public boolean containsKey(Object key)
    {
      synchronized (mutex)
        {
          return m.containsKey(key);
        }
    }

    public boolean containsValue(Object value)
    {
      synchronized (mutex)
        {
          return m.containsValue(value);
        }
    }

    // This is one of the ickiest cases of nesting I've ever seen. It just
    // means "return a SynchronizedSet, except that the iterator() method
    // returns an SynchronizedIterator whose next() method returns a
    // synchronized wrapper around its normal return value".
    public Set entrySet()
    {
      // Define this here to spare some nesting.
      class SynchronizedMapEntry implements Map.Entry
      {
        final Map.Entry e;
        SynchronizedMapEntry(Object o)
        {
          e = (Map.Entry) o;
        }
        public boolean equals(Object o)
        {
          synchronized (mutex)
            {
              return e.equals(o);
            }
        }
        public Object getKey()
        {
          synchronized (mutex)
            {
              return e.getKey();
            }
        }
        public Object getValue()
        {
          synchronized (mutex)
            {
              return e.getValue();
            }
        }
        public int hashCode()
        {
          synchronized (mutex)
            {
              return e.hashCode();
            }
        }
        public Object setValue(Object value)
        {
          synchronized (mutex)
            {
              r