abstractcollection.java

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   * object. If it is equal, it is removed by the iterator's remove method
   * (thus this method will fail with an UnsupportedOperationException if
   * the Iterator's remove method does). After the first element has been
   * removed, true is returned; if the end of the collection is reached, false
   * is returned.
   *
   * @param o the object to remove from this collection
   * @return true if the remove operation caused the Collection to change, or
   *         equivalently if the collection did contain o.
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @see Iterator#remove()
   */
  public boolean remove(Object o)
  {
    Iterator itr = iterator();
    int pos = size();
    while (--pos >= 0)
      if (equals(o, itr.next()))
        {
          itr.remove();
          return true;
        }
    return false;
  }

  /**
   * Remove from this collection all its elements that are contained in a given
   * collection (optional operation). This implementation iterates over this
   * collection, and for each element tests if it is contained in the given
   * collection. If so, it is removed by the Iterator's remove method (thus
   * this method will fail with an UnsupportedOperationException if the
   * Iterator's remove method does).
   *
   * @param c the collection to remove the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @see Iterator#remove()
   */
  public boolean removeAll(Collection c)
  {
    return removeAllInternal(c);
  }

  /**
   * Remove from this collection all its elements that are contained in a given
   * collection (optional operation). This implementation iterates over this
   * collection, and for each element tests if it is contained in the given
   * collection. If so, it is removed by the Iterator's remove method (thus
   * this method will fail with an UnsupportedOperationException if the
   * Iterator's remove method does). This method is necessary for ArrayList,
   * which cannot publicly override removeAll but can optimize this call.
   *
   * @param c the collection to remove the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @see Iterator#remove()
   */
  boolean removeAllInternal(Collection c)
  {
    Iterator itr = iterator();
    boolean modified = false;
    int pos = size();
    while (--pos >= 0)
      if (c.contains(itr.next()))
        {
          itr.remove();
          modified = true;
        }
    return modified;
  }

  /**
   * Remove from this collection all its elements that are not contained in a
   * given collection (optional operation). This implementation iterates over
   * this collection, and for each element tests if it is contained in the
   * given collection. If not, it is removed by the Iterator's remove method
   * (thus this method will fail with an UnsupportedOperationException if
   * the Iterator's remove method does).
   *
   * @param c the collection to retain the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @see Iterator#remove()
   */
  public boolean retainAll(Collection c)
  {
    return retainAllInternal(c);
  }

  /**
   * Remove from this collection all its elements that are not contained in a
   * given collection (optional operation). This implementation iterates over
   * this collection, and for each element tests if it is contained in the
   * given collection. If not, it is removed by the Iterator's remove method
   * (thus this method will fail with an UnsupportedOperationException if
   * the Iterator's remove method does). This method is necessary for
   * ArrayList, which cannot publicly override retainAll but can optimize
   * this call.
   *
   * @param c the collection to retain the elements of
   * @return true if the remove operation caused the Collection to change
   * @throws UnsupportedOperationException if this collection's Iterator
   *         does not support the remove method
   * @see Iterator#remove()
   */
  boolean retainAllInternal(Collection c)
  {
    Iterator itr = iterator();
    boolean modified = false;
    int pos = size();
    while (--pos >= 0)
      if (!c.contains(itr.next()))
        {
          itr.remove();
          modified = true;
        }
    return modified;
  }

  /**
   * Return an array containing the elements of this collection. This
   * implementation creates an Object array of size size() and then iterates
   * over the collection, setting each element of the array from the value
   * returned by the iterator. The returned array is safe, and is not backed
   * by the collection.
   *
   * @return an array containing the elements of this collection
   */
  public Object[] toArray()
  {
    Iterator itr = iterator();
    int size = size();
    Object[] a = new Object[size];
    for (int pos = 0; pos < size; pos++)
      a[pos] = itr.next();
    return a;
  }

  /**
   * Copy the collection into a given array if it will fit, or into a
   * dynamically created array of the same run-time type as the given array if
   * not. If there is space remaining in the array, the first element after the
   * end of the collection is set to null (this is only useful if the
   * collection is known to contain no null elements, however). This
   * implementation first tests whether the given array is large enough to hold
   * all the elements of the collection. If not, the reflection API is used to
   * allocate a new array of the same run-time type. Next an iterator is
   * obtained over the collection and the elements are placed in the array as
   * they are returned by the iterator. Finally the first spare element, if
   * any, of the array is set to null, and the created array is returned.
   * The returned array is safe; it is not backed by the collection. Note that
   * null may not mark the last element, if the collection allows null
   * elements.
   *
   * @param a the array to copy into, or of the correct run-time type
   * @return the array that was produced
   * @throws NullPointerException if the given array is null
   * @throws ArrayStoreException if the type of the array precludes holding
   *         one of the elements of the Collection
   */
  public Object[] toArray(Object[] a)
  {
    int size = size();
    if (a.length < size)
      a = (Object[]) Array.newInstance(a.getClass().getComponentType(),
                                       size);
    else if (a.length > size)
      a[size] = null;

    Iterator itr = iterator();
    for (int pos = 0; pos < size; pos++)
      a[pos] = itr.next();

    return a;
  }

  /**
   * Creates a String representation of the Collection. The string returned is
   * of the form "[a, b, ...]" where a and b etc are the results of calling
   * toString on the elements of the collection. This implementation obtains an
   * Iterator over the Collection and adds each element to a StringBuffer as it
   * is returned by the iterator.
   *
   * @return a String representation of the Collection
   */
  public String toString()
  {
    Iterator itr = iterator();
    StringBuffer r = new StringBuffer("[");
    for (int pos = size(); pos > 0; pos--)
      {
        r.append(itr.next());
        if (pos > 1)
          r.append(", ");
      }
    r.append("]");
    return r.toString();
  }

  /**
   * 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();
  }
}