arraydeque.java

来自「SRI international 发布的OAA框架软件」· Java 代码 · 共 780 行 · 第 1/2 页

        int mask = elements.length - 1;
        int i = (tail - 1) & mask;
        Object x;
        while ( (x = elements[i]) != null) {
            if (e.equals(x)) {
                delete(i);
                return true;
            }
            i = (i - 1) & mask;
        }
        return false;
    }

    // *** Queue methods ***

    /**
     * Inserts the specified element to the end of this deque.
     *
     * <p>This method is equivalent to {@link #offerLast}.
     *
     * @param e the element to insert
     * @return <tt>true</tt> (as per the spec for {@link Queue#offer})
     * @throws NullPointerException if <tt>e</tt> is null
     */
    public boolean offer(Object e) {
        return offerLast(e);
    }

    /**
     * Inserts the specified element to the end of this deque.
     *
     * <p>This method is equivalent to {@link #addLast}.
     *
     * @param e the element to insert
     * @return <tt>true</tt> (as per the spec for {@link Collection#add})
     * @throws NullPointerException if <tt>e</tt> is null
     */
    public boolean add(Object e) {
        addLast(e);
        return true;
    }

    /**
     * Retrieves and removes the head of the queue represented by
     * this deque, or <tt>null</tt> if this deque is empty.  In other words,
     * retrieves and removes the first element of this deque, or <tt>null</tt>
     * if this deque is empty.
     *
     * <p>This method is equivalent to {@link #pollFirst}.
     *
     * @return the first element of this deque, or <tt>null</tt> if
     *     this deque is empty
     */
    public Object poll() {
        return pollFirst();
    }

    /**
     * Retrieves and removes the head of the queue represented by this deque.
     * This method differs from the <tt>poll</tt> method in that it throws an
     * exception if this deque is empty.
     *
     * <p>This method is equivalent to {@link #removeFirst}.
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
     */
    public Object remove() {
        return removeFirst();
    }

    /**
     * Retrieves, but does not remove, the head of the queue represented by
     * this deque, returning <tt>null</tt> if this deque is empty.
     *
     * <p>This method is equivalent to {@link #peekFirst}
     *
     * @return the head of the queue represented by this deque, or
     *     <tt>null</tt> if this deque is empty
     */
    public Object peek() {
        return peekFirst();
    }

    /**
     * Retrieves, but does not remove, the head of the queue represented by
     * this deque.  This method differs from the <tt>peek</tt> method only in
     * that it throws an exception if this deque is empty.
     *
     * <p>This method is equivalent to {@link #getFirst}
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
     */
    public Object element() {
        return getFirst();
    }

    // *** Stack methods ***

    /**
     * Pushes an element onto the stack represented by this deque.  In other
     * words, inserts the element to the front this deque.
     *
     * <p>This method is equivalent to {@link #addFirst}.
     *
     * @param e the element to push
     * @throws NullPointerException if <tt>e</tt> is null
     */
    public void push(Object e) {
        addFirst(e);
    }

    /**
     * Pops an element from the stack represented by this deque.  In other
     * words, removes and returns the the first element of this deque.
     *
     * <p>This method is equivalent to {@link #removeFirst()}.
     *
     * @return the element at the front of this deque (which is the top
     *     of the stack represented by this deque)
     * @throws NoSuchElementException if this deque is empty
     */
    public Object pop() {
        return removeFirst();
    }

    /**
     * Remove the element at the specified position in the elements array,
     * adjusting head, tail, and size as necessary.  This can result in
     * motion of elements backwards or forwards in the array.
     *
     * <p>This method is called delete rather than remove to emphasize the
     * that that its semantics differ from those of List.remove(int).
     *
     * @return true if elements moved backwards
     */
    private boolean delete(int i) {
        // Case 1: Deque doesn't wrap
        // Case 2: Deque does wrap and removed element is in the head portion
        if ((head < tail || tail == 0) || i >= head) {
            System.arraycopy(elements, head, elements, head + 1, i - head);
            elements[head] = null;
            head = (head + 1) & (elements.length - 1);
            return false;
        }

        // Case 3: Deque wraps and removed element is in the tail portion
        tail--;
        System.arraycopy(elements, i + 1, elements, i, tail - i);
        elements[tail] = null;
        return true;
    }

    // *** Collection Methods ***

    /**
     * Returns the number of elements in this deque.
     *
     * @return the number of elements in this deque
     */
    public int size() {
        return (tail - head) & (elements.length - 1);
    }

    /**
     * Returns <tt>true</tt> if this collection contains no elements.<p>
     *
     * @return <tt>true</tt> if this collection contains no elements.
     */
    public boolean isEmpty() {
        return head == tail;
    }

    /**
     * Returns an iterator over the elements in this deque.  The elements
     * will be ordered from first (head) to last (tail).  This is the same
     * order that elements would be dequeued (via successive calls to
     * {@link #remove} or popped (via successive calls to {@link #pop}).
     *
     * @return an <tt>Iterator</tt> over the elements in this deque
     */
    public Iterator iterator() {
        return new DeqIterator();
    }

    private class DeqIterator implements Iterator {
        /**
         * Index of element to be returned by subsequent call to next.
         */
        private int cursor = head;

        /**
         * Tail recorded at construction (also in remove), to stop
         * iterator and also to check for comodification.
         */
        private int fence = tail;

        /**
         * Index of element returned by most recent call to next.
         * Reset to -1 if element is deleted by a call to remove.
         */
        private int lastRet = -1;

        public boolean hasNext() {
            return cursor != fence;
        }

        public Object next() {
            Object result;
            if (cursor == fence)
                throw new NoSuchElementException();
            // This check doesn't catch all possible comodifications,
            // but does catch the ones that corrupt traversal
            if (tail != fence || (result = elements[cursor]) == null)
                throw new ConcurrentModificationException();
            lastRet = cursor;
            cursor = (cursor + 1) & (elements.length - 1);
            return result;
        }

        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            if (delete(lastRet))
                cursor--;
            lastRet = -1;
            fence = tail;
        }
    }

    /**
     * Returns <tt>true</tt> if this deque contains the specified
     * element.  More formally, returns <tt>true</tt> if and only if this
     * deque contains at least one element <tt>e</tt> such that
     * <tt>e.equals(o)</tt>.
     *
     * @param o object to be checked for containment in this deque
     * @return <tt>true</tt> if this deque contains the specified element
     */
    public boolean contains(Object o) {
        if (o == null)
            return false;
        int mask = elements.length - 1;
        int i = head;
        Object x;
        while ( (x = elements[i]) != null) {
            if (o.equals(x))
                return true;
            i = (i + 1) & mask;
        }
        return false;
    }

    /**
     * Removes a single instance of the specified element from this deque.
     * This method is equivalent to {@link #removeFirstOccurrence}.
     *
     * @param e element to be removed from this deque, if present
     * @return <tt>true</tt> if this deque contained the specified element
     */
    public boolean remove(Object e) {
        return removeFirstOccurrence(e);
    }

    /**
     * Removes all of the elements from this deque.
     */
    public void clear() {
        int h = head;
        int t = tail;
        if (h != t) { // clear all cells
            head = tail = 0;
            int i = h;
            int mask = elements.length - 1;
            do {
                elements[i] = null;
                i = (i + 1) & mask;
            } while(i != t);
        }
    }

    /**
     * Returns an array containing all of the elements in this list
     * in the correct order.
     *
     * @return an array containing all of the elements in this list
     * 	       in the correct order
     */
    public Object[] toArray() {
        return copyElements(new Object[size()]);
    }

    /**
     * Returns an array containing all of the elements in this deque in the
     * correct order; the runtime type of the returned array is that of the
     * specified array.  If the deque fits in the specified array, it is
     * returned therein.  Otherwise, a new array is allocated with the runtime
     * type of the specified array and the size of this deque.
     *
     * <p>If the deque fits in the specified array with room to spare (i.e.,
     * the array has more elements than the deque), the element in the array
     * immediately following the end of the collection is set to <tt>null</tt>.
     *
     * @param a the array into which the elements of the deque are to
     *		be stored, if it is big enough; otherwise, a new array of the
     * 		same runtime type is allocated for this purpose
     * @return an array containing the elements of the deque
     * @throws ArrayStoreException if the runtime type of a is not a supertype
     *         of the runtime type of every element in this deque
     */
    public Object[] toArray(Object[] a) {
        int size = size();
        if (a.length < size)
            a = (Object[])java.lang.reflect.Array.newInstance(
                    a.getClass().getComponentType(), size);
        copyElements(a);
        if (a.length > size)
            a[size] = null;
        return a;
    }

    // *** Object methods ***

    /**
     * Returns a copy of this deque.
     *
     * @return a copy of this deque
     */
    public Object clone() {
        try {
            ArrayDeque result = (ArrayDeque) super.clone();
            // These two lines are currently faster than cloning the array:
            result.elements = (Object[]) new Object[elements.length];
            System.arraycopy(elements, 0, result.elements, 0, elements.length);
            return result;

        } catch (CloneNotSupportedException e) {
            throw new AssertionError();
        }
    }

    /**
     * Appease the serialization gods.
     */
    private static final long serialVersionUID = 2340985798034038923L;

    /**
     * Serialize this deque.
     *
     * @serialData The current size (<tt>int</tt>) of the deque,
     * followed by all of its elements (each an object reference) in
     * first-to-last order.
     */
    private void writeObject(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();

        // Write out size
        int size = size();
        s.writeInt(size);

        // Write out elements in order.
        int i = head;
        int mask = elements.length - 1;
        for (int j = 0; j < size; j++) {
            s.writeObject(elements[i]);
            i = (i + 1) & mask;
        }
    }

    /**
     * Deserialize this deque.
     */
    private void readObject(ObjectInputStream s)
            throws IOException, ClassNotFoundException {
        s.defaultReadObject();

        // Read in size and allocate array
        int size = s.readInt();
        allocateElements(size);
        head = 0;
        tail = size;

        // Read in all elements in the proper order.
        for (int i = 0; i < size; i++)
            elements[i] = (Object)s.readObject();

    }
}