abstractmap.java

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   * @throws ClassCastException if the key or value is of the wrong type
   * @throws IllegalArgumentException if something about this key or value
   *         prevents it from existing in this map
   * @throws NullPointerException if the map forbids null keys or values
   * @see #containsKey(Object)
   */
  public Object put(Object key, Object value)
  {
    throw new UnsupportedOperationException();
  }

  /**
   * Copies all entries of the given map to this one (optional operation). If
   * the map already contains a key, its value is replaced. This implementation
   * simply iterates over the map's entrySet(), calling <code>put</code>,
   * so it is not supported if puts are not.
   *
   * @param m the mapping to load into this map
   * @throws UnsupportedOperationException if the operation is not supported
   * @throws ClassCastException if a key or value is of the wrong type
   * @throws IllegalArgumentException if something about a key or value
   *         prevents it from existing in this map
   * @throws NullPointerException if the map forbids null keys or values, or
   *         if <code>m</code> is null.
   * @see #put(Object, Object)
   */
  public void putAll(Map m)
  {
    Iterator entries = m.entrySet().iterator();
    int pos = m.size();
    while (--pos >= 0)
      {
        Map.Entry entry = (Map.Entry) entries.next();
        put(entry.getKey(), entry.getValue());
      }
  }

  /**
   * Removes the mapping for this key if present (optional operation). This
   * implementation iterates over the entrySet searching for a matching
   * key, at which point it calls the iterator's <code>remove</code> method.
   * It returns the result of <code>getValue()</code> on the entry, if found,
   * or null if no entry is found. Note that maps which permit null values
   * may also return null if the key was removed.  If the entrySet does not
   * support removal, this will also fail. This is O(n), so many
   * implementations override it for efficiency.
   *
   * @param key the key to remove
   * @return the value the key mapped to, or null if not present
   * @throws UnsupportedOperationException if deletion is unsupported
   * @see Iterator#remove()
   */
  public Object remove(Object key)
  {
    Iterator entries = entrySet().iterator();
    int pos = size();
    while (--pos >= 0)
      {
        Map.Entry entry = (Map.Entry) entries.next();
        if (equals(key, entry.getKey()))
          {
            // Must get the value before we remove it from iterator.
            Object r = entry.getValue();
            entries.remove();
            return r;
          }
      }
    return null;
  }

  /**
   * Returns the number of key-value mappings in the map. If there are more
   * than Integer.MAX_VALUE mappings, return Integer.MAX_VALUE. This is
   * implemented as <code>entrySet().size()</code>.
   *
   * @return the number of mappings
   * @see Set#size()
   */
  public int size()
  {
    return entrySet().size();
  }

  /**
   * Returns a String representation of this map. This is a listing of the
   * map entries (which are specified in Map.Entry as being
   * <code>getKey() + "=" + getValue()</code>), separated by a comma and
   * space (", "), and surrounded by braces ('{' and '}'). This implementation
   * uses a StringBuffer and iterates over the entrySet to build the String.
   * Note that this can fail with an exception if underlying keys or
   * values complete abruptly in toString().
   *
   * @return a String representation
   * @see Map.Entry#toString()
   */
  public String toString()
  {
    Iterator entries = entrySet().iterator();
    StringBuffer r = new StringBuffer("{");
    for (int pos = size(); pos > 0; pos--)
      {
        Map.Entry entry = (Map.Entry) entries.next();
        r.append(entry.getKey());
        r.append('=');
        r.append(entry.getValue());
        if (pos > 1)
          r.append(", ");
      }
    r.append("}");
    return r.toString();
  }

  /**
   * Returns a collection or bag view of this map's values. The collection
   * is backed by the map, so changes in one show up in the other.
   * Modifications while an iteration is in progress produce undefined
   * behavior. The collection supports removal if entrySet() does, but
   * does not support element addition.
   * <p>
   *
   * This implementation creates an AbstractCollection, where the iterator
   * wraps the entrySet iterator, size defers to the Map's size, and contains
   * defers to the Map's containsValue. The collection is created on first
   * use, and returned on subsequent uses, although since no synchronization
   * occurs, there is a slight possibility of creating two collections.
   *
   * @return a Collection view of the values
   * @see Collection#iterator()
   * @see #size()
   * @see #containsValue(Object)
   * @see #keySet()
   */
  public Collection values()
  {
    if (values == null)
      values = new AbstractCollection()
      {
        public int size()
        {
          return AbstractMap.this.size();
        }

        public boolean contains(Object value)
        {
          return containsValue(value);
        }

        public Iterator iterator()
        {
          return new Iterator()
          {
            private final Iterator map_iterator = entrySet().iterator();

            public boolean hasNext()
            {
              return map_iterator.hasNext();
            }

            public Object next()
            {
              return ((Map.Entry) map_iterator.next()).getValue();
            }

            public void remove()
            {
              map_iterator.remove();
            }
          };
        }
      };
    return values;
  }

  /**
   * Compare two objects according to Collection semantics.
   *
   * @param o1 the first object
   * @param o2 the second object
   * @return o1 == null ? o2 == null : o1.equals(o2)
   */
  // Package visible for use throughout java.util.
  // It may be inlined since it is final.
  static final boolean equals(Object o1, Object o2)
  {
    return o1 == null ? o2 == null : o1.equals(o2);
  }

  /**
   * Hash an object according to Collection semantics.
   *
   * @param o the object to hash
   * @return o1 == null ? 0 : o1.hashCode()
   */
  // Package visible for use throughout java.util.
  // It may be inlined since it is final.
  static final int hashCode(Object o)
  {
    return o == null ? 0 : o.hashCode();
  }

  /**
   * A class which implements Map.Entry. It is shared by HashMap, TreeMap,
   * Hashtable, and Collections. It is not specified by the JDK, but makes
   * life much easier.
   *
   * @author Jon Zeppieri
   * @author Eric Blake <[e-mail]>
   */
  // XXX - FIXME Use fully qualified implements as gcj 3.1 workaround.
  static class BasicMapEntry implements Map.Entry
  {
    /**
     * The key. Package visible for direct manipulation.
     */
    Object key;

    /**
     * The value. Package visible for direct manipulation.
     */
    Object value;

    /**
     * Basic constructor initializes the fields.
     * @param newKey the key
     * @param newValue the value
     */
    BasicMapEntry(Object newKey, Object newValue)
    {
      key = newKey;
      value = newValue;
    }

    /**
     * Compares the specified object with this entry. Returns true only if
     * the object is a mapping of identical key and value. In other words,
     * this must be:<br>
     * <pre>(o instanceof Map.Entry)
     *       && (getKey() == null ? ((HashMap) o).getKey() == null
     *           : getKey().equals(((HashMap) o).getKey()))
     *       && (getValue() == null ? ((HashMap) o).getValue() == null
     *           : getValue().equals(((HashMap) o).getValue()))</pre>
     *
     * @param o the object to compare
     * @return <code>true</code> if it is equal
     */
    public final boolean equals(Object o)
    {
      if (! (o instanceof Map.Entry))
        return false;
      // Optimize for our own entries.
      if (o instanceof BasicMapEntry)
        {
          BasicMapEntry e = (BasicMapEntry) o;
          return (AbstractMap.equals(key, e.key)
                  && AbstractMap.equals(value, e.value));
        }
      Map.Entry e = (Map.Entry) o;
      return (AbstractMap.equals(key, e.getKey())
              && AbstractMap.equals(value, e.getValue()));
    }

    /**
     * Get the key corresponding to this entry.
     *
     * @return the key
     */
    public final Object getKey()
    {
      return key;
    }

    /**
     * Get the value corresponding to this entry. If you already called
     * Iterator.remove(), the behavior undefined, but in this case it works.
     *
     * @return the value
     */
    public final Object getValue()
    {
      return value;
    }

    /**
     * Returns the hash code of the entry.  This is defined as the exclusive-or
     * of the hashcodes of the key and value (using 0 for null). In other
     * words, this must be:<br>
     * <pre>(getKey() == null ? 0 : getKey().hashCode())
     *       ^ (getValue() == null ? 0 : getValue().hashCode())</pre>
     *
     * @return the hash code
     */
    public final int hashCode()
    {
      return (AbstractMap.hashCode(key) ^ AbstractMap.hashCode(value));
    }

    /**
     * Replaces the value with the specified object. This writes through
     * to the map, unless you have already called Iterator.remove(). It
     * may be overridden to restrict a null value.
     *
     * @param newVal the new value to store
     * @return the old value
     * @throws NullPointerException if the map forbids null values
     */
    public Object setValue(Object newVal)
    {
      Object r = value;
      value = newVal;
      return r;
    }

    /**
     * This provides a string representation of the entry. It is of the form
     * "key=value", where string concatenation is used on key and value.
     *
     * @return the string representation
     */
    public final String toString()
    {
      return key + "=" + value;
    }
  } // class BasicMapEntry
}