collections.java

gcc的组建

            a[swap] = i.previous();
          }
        else
          o = l.set(swap, i.previous());

	i.set(o);
      }
  }


  /**
   * Obtain an immutable Set consisting of a single element. The return value
   * of this method is Serializable.
   *
   * @param o the single element
   * @return an immutable Set containing only o
   * @see Serializable
   */
  public static Set singleton(Object o)
  {
    return new SingletonSet(o);
  }

  /**
   * The implementation of {@link #singleton(Object)}. This class name
   * is required for compatibility with Sun's JDK serializability.
   *
   * @author Eric Blake ([e-mail])
   */
  private static final class SingletonSet extends AbstractSet
    implements Serializable
  {
    /**
     * Compatible with JDK 1.4.
     */
    private static final long serialVersionUID = 3193687207550431679L;


    /**
     * The single element; package visible for use in nested class.
     * @serial the singleton
     */
    final Object element;

    /**
     * Construct a singleton.
     * @param o the element
     */
    SingletonSet(Object o)
    {
      element = o;
    }

    /**
     * The size: always 1!
     * @return 1.
     */
    public int size()
    {
      return 1;
    }

    /**
     * Returns an iterator over the lone element.
     */
    public Iterator iterator()
    {
      return new Iterator()
      {
	/**
	 * Flag to indicate whether or not the element has
	 * been retrieved.
	 */
        private boolean hasNext = true;

	/**
	 * Returns <code>true</code> if elements still remain to be
	 * iterated through.
	 *
	 * @return <code>true</code> if the element has not yet been returned.
	 */
        public boolean hasNext()
        {
          return hasNext;
        }

	/**
	 * Returns the element.
	 *
	 * @return The element used by this singleton.
	 * @throws NoSuchElementException if the object
	 *         has already been retrieved.
	 */ 
        public Object next()
        {
          if (hasNext)
          {
            hasNext = false;
            return element;
          }
          else
            throw new NoSuchElementException();
        }

	/**
	 * Removes the element from the singleton.
	 * As this set is immutable, this will always
	 * throw an exception.
	 *
	 * @throws UnsupportedOperationException as the
	 *         singleton set doesn't support
	 *         <code>remove()</code>.
	 */
        public void remove()
        {
          throw new UnsupportedOperationException();
        }
      };
    }

    // The remaining methods are optional, but provide a performance
    // advantage by not allocating unnecessary iterators in AbstractSet.
    /**
     * The set only contains one element.
     *
     * @param o The object to search for.
     * @return <code>true</code> if o == the element of the singleton.
     */
    public boolean contains(Object o)
    {
      return equals(o, element);
    }

    /**
     * This is true if the other collection only contains the element.
     *
     * @param c A collection to compare against this singleton.
     * @return <code>true</code> if c only contains either no elements or
     *         elements equal to the element in this singleton.
     */
    public boolean containsAll(Collection c)
    {
      Iterator i = c.iterator();
      int pos = c.size();
      while (--pos >= 0)
        if (! equals(i.next(), element))
          return false;
      return true;
    }

    /**
     * The hash is just that of the element.
     * 
     * @return The hashcode of the element.
     */
    public int hashCode()
    {
      return hashCode(element);
    }

    /**
     * Returning an array is simple.
     *
     * @return An array containing the element.
     */
    public Object[] toArray()
    {
      return new Object[] {element};
    }

    /**
     * Obvious string.
     *
     * @return The string surrounded by enclosing
     *         square brackets.
     */
    public String toString()
    {
      return "[" + element + "]";
    }
  } // class SingletonSet

  /**
   * Obtain an immutable List consisting of a single element. The return value
   * of this method is Serializable, and implements RandomAccess.
   *
   * @param o the single element
   * @return an immutable List containing only o
   * @see Serializable
   * @see RandomAccess
   * @since 1.3
   */
  public static List singletonList(Object o)
  {
    return new SingletonList(o);
  }

  /**
   * The implementation of {@link #singletonList(Object)}. This class name
   * is required for compatibility with Sun's JDK serializability.
   *
   * @author Eric Blake ([e-mail])
   */
  private static final class SingletonList extends AbstractList
    implements Serializable, RandomAccess
  {
    /**
     * Compatible with JDK 1.4.
     */
    private static final long serialVersionUID = 3093736618740652951L;

    /**
     * The single element.
     * @serial the singleton
     */
    private final Object element;

    /**
     * Construct a singleton.
     * @param o the element
     */
    SingletonList(Object o)
    {
      element = o;
    }

    /**
     * The size: always 1!
     * @return 1.
     */
    public int size()
    {
      return 1;
    }

    /**
     * Only index 0 is valid.
     * @param index The index of the element
     *        to retrieve.
     * @return The singleton's element if the
     *         index is 0.
     * @throws IndexOutOfBoundsException if
     *         index is not 0.
     */
    public Object get(int index)
    {
      if (index == 0)
        return element;
      throw new IndexOutOfBoundsException();
    }

    // The remaining methods are optional, but provide a performance
    // advantage by not allocating unnecessary iterators in AbstractList.
    /**
     * The set only contains one element.
     *
     * @param o The object to search for.
     * @return <code>true</code> if o == the singleton element.
     */
    public boolean contains(Object o)
    {
      return equals(o, element);
    }

    /**
     * This is true if the other collection only contains the element.
     *
     * @param c A collection to compare against this singleton.
     * @return <code>true</code> if c only contains either no elements or
     *         elements equal to the element in this singleton.
     */
    public boolean containsAll(Collection c)
    {
      Iterator i = c.iterator();
      int pos = c.size();
      while (--pos >= 0)
        if (! equals(i.next(), element))
          return false;
      return true;
    }

    /**
     * Speed up the hashcode computation.
     *
     * @return The hashcode of the list, based
     *         on the hashcode of the singleton element.
     */
    public int hashCode()
    {
      return 31 + hashCode(element);
    }

    /**
     * Either the list has it or not.
     *
     * @param o The object to find the first index of.
     * @return 0 if o is the singleton element, -1 if not.
     */
    public int indexOf(Object o)
    {
      return equals(o, element) ? 0 : -1;
    }

    /**
     * Either the list has it or not.
     *
     * @param o The object to find the last index of.
     * @return 0 if o is the singleton element, -1 if not.
     */
    public int lastIndexOf(Object o)
    {
      return equals(o, element) ? 0 : -1;
    }

    /**
     * Sublists are limited in scope.
     * 
     * @param from The starting bound for the sublist.
     * @param to The ending bound for the sublist.
     * @return Either an empty list if both bounds are
     *         0 or 1, or this list if the bounds are 0 and 1.
     * @throws IllegalArgumentException if <code>from > to</code>
     * @throws IndexOutOfBoundsException if either bound is greater
     *         than 1.
     */
    public List subList(int from, int to)
    {
      if (from == to && (to == 0 || to == 1))
        return EMPTY_LIST;
      if (from == 0 && to == 1)
        return this;
      if (from > to)
        throw new IllegalArgumentException();
      throw new IndexOutOfBoundsException();
    }

    /**
     * Returning an array is simple.
     *
     * @return An array containing the element.
     */
    public Object[] toArray()
    {
      return new Object[] {element};
    }

    /**
     * Obvious string.
     *
     * @return The string surrounded by enclosing
     *         square brackets. 
     */
    public String toString()
    {
      return "[" + element + "]";
    }
  } // class SingletonList

  /**
   * Obtain an immutable Map consisting of a single key-value pair.
   * The return value of this method is Serializable.
   *
   * @param key the single key
   * @param value the single value
   * @return an immutable Map containing only the single key-value pair
   * @see Serializable
   * @since 1.3
   */
  public static Map singletonMap(Object key, Object value)
  {
    return new SingletonMap(key, value);
  }

  /**
   * The implementation of {@link #singletonMap(Object, Object)}. This class
   * name is required for compatibility with Sun's JDK serializability.
   *
   * @author Eric Blake ([e-mail])
   */
  private static final class SingletonMap extends AbstractMap
    implements Serializable
  {
    /**
     * Compatible with JDK 1.4.
     */
    private static final long serialVersionUID = -6979724477215052911L;

    /**
     * The single key.
     * @serial the singleton key
     */
    private final Object k;

    /**
     * The corresponding value.
     * @serial the singleton value
     */
    private final Object v;

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

    /**
     * Construct a singleton.
     * @param key the key
     * @param value the value
     */
    SingletonMap(Object key, Object value)
    {
      k = key;
      v = value;
    }

    /**
     * There is a single immutable entry.
     *
     * @return A singleton containing the map entry.
     */
    public Set entrySet()
    {
      if (entries == null)
        entries = singleton(new AbstractMap.BasicMapEntry(k, v)
        {
	  /**
	   * Sets the value of the map entry to the supplied value.
	   * An exception is always thrown, as the map is immutable.
	   *
	   * @param o The new value.
	   * @return The old value.
	   * @throws UnsupportedOperationException as setting the value
	   *         is not supported.
	   */
          public Object setValue(Object o)
          {
            throw new UnsupportedOperationException();
          }
        });
      return entries;
    }

    // The remaining methods are optional, but provide a performance
    // advantage by not allocating unnecessary iterators in AbstractMap.
    /**
     * Single entry.
     *
     * @param key The key to look for.
     * @return <code>true</code> if the key is the same as the one used by
     *         this map.
     */
    public boolean containsKey(Object key)
    {