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/* |
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* Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Sun designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Sun in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
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* CA 95054 USA or visit www.sun.com if you need additional information or |
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* have any questions. |
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*/ |
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|
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package java.util; |
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|
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/** |
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* Linked list implementation of the {@code List} interface. Implements all |
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* optional list operations, and permits all elements (including |
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* {@code null}). In addition to implementing the {@code List} interface, |
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* the {@code LinkedList} class provides uniformly named methods to |
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* {@code get}, {@code remove} and {@code insert} an element at the |
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* beginning and end of the list. These operations allow linked lists to be |
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* used as a stack, {@linkplain Queue queue}, or {@linkplain Deque |
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* double-ended queue}. |
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* |
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* <p>The class implements the {@code Deque} interface, providing |
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* first-in-first-out queue operations for {@code add}, |
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* {@code poll}, along with other stack and deque operations. |
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* |
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* <p>All of the operations perform as could be expected for a doubly-linked |
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* list. Operations that index into the list will traverse the list from |
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* the beginning or the end, whichever is closer to the specified index. |
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* |
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* <p><strong>Note that this implementation is not synchronized.</strong> |
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* If multiple threads access a linked list concurrently, and at least |
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* one of the threads modifies the list structurally, it <i>must</i> be |
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* synchronized externally. (A structural modification is any operation |
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* that adds or deletes one or more elements; merely setting the value of |
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* an element is not a structural modification.) This is typically |
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* accomplished by synchronizing on some object that naturally |
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* encapsulates the list. |
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* |
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* If no such object exists, the list should be "wrapped" using the |
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* {@link Collections#synchronizedList Collections.synchronizedList} |
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* method. This is best done at creation time, to prevent accidental |
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* unsynchronized access to the list:<pre> |
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* List list = Collections.synchronizedList(new LinkedList(...));</pre> |
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* |
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* <p>The iterators returned by this class's {@code iterator} and |
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* {@code listIterator} methods are <i>fail-fast</i>: if the list is |
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* structurally modified at any time after the iterator is created, in |
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* any way except through the Iterator's own {@code remove} or |
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* {@code add} methods, the iterator will throw a {@link |
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* ConcurrentModificationException}. Thus, in the face of concurrent |
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* modification, the iterator fails quickly and cleanly, rather than |
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* risking arbitrary, non-deterministic behavior at an undetermined |
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* time in the future. |
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* |
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* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
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* as it is, generally speaking, impossible to make any hard guarantees in the |
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* presence of unsynchronized concurrent modification. Fail-fast iterators |
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* throw {@code ConcurrentModificationException} on a best-effort basis. |
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* Therefore, it would be wrong to write a program that depended on this |
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* exception for its correctness: <i>the fail-fast behavior of iterators |
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* should be used only to detect bugs.</i> |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @author Josh Bloch |
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* @see List |
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* @see ArrayList |
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* @since 1.2 |
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* @param <E> the type of elements held in this collection |
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*/ |
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|
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public class LinkedList<E> |
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extends AbstractSequentialList<E> |
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implements List<E>, Deque<E>, Cloneable, java.io.Serializable |
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{ |
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transient int size = 0; |
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|
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/** |
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* Pointer to first node. |
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* Invariant: (first == null && last == null) || |
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* (first.prev == null && first.item != null) |
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*/ |
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transient Node<E> first; |
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|
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/** |
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* Pointer to last node. |
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* Invariant: (first == null && last == null) || |
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* (last.next == null && last.item != null) |
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*/ |
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transient Node<E> last; |
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|
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/** |
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* Constructs an empty list. |
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*/ |
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public LinkedList() { |
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} |
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|
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/** |
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* Constructs a list containing the elements of the specified |
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* collection, in the order they are returned by the collection's |
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* iterator. |
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* |
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* @param c the collection whose elements are to be placed into this list |
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* @throws NullPointerException if the specified collection is null |
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*/ |
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public LinkedList(Collection<? extends E> c) { |
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this(); |
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addAll(c); |
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} |
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|
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/** |
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* Links e as first element. |
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*/ |
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private void linkFirst(E e) { |
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final Node<E> f = first; |
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final Node<E> newNode = new Node<E>(null, e, f); |
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first = newNode; |
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if (f == null) |
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last = newNode; |
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else |
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f.prev = newNode; |
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size++; |
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modCount++; |
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} |
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|
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/** |
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* Links e as last element. |
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*/ |
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void linkLast(E e) { |
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final Node<E> l = last; |
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final Node<E> newNode = new Node<E>(l, e, null); |
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last = newNode; |
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if (l == null) |
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first = newNode; |
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else |
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l.next = newNode; |
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size++; |
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modCount++; |
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} |
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|
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/** |
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* Inserts element e before non-null Node succ. |
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*/ |
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void linkBefore(E e, Node<E> succ) { |
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// assert succ != null; |
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final Node<E> pred = succ.prev; |
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final Node<E> newNode = new Node<E>(pred, e, succ); |
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succ.prev = newNode; |
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if (pred == null) |
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first = newNode; |
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else |
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pred.next = newNode; |
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size++; |
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modCount++; |
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} |
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|
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/** |
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* Unlinks non-null first node f. |
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*/ |
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private E unlinkFirst(Node<E> f) { |
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// assert f == first && f != null; |
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final E element = f.item; |
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final Node<E> next = f.next; |
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f.item = null; |
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f.next = null; // help GC |
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first = next; |
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if (next == null) |
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last = null; |
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else |
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next.prev = null; |
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size--; |
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modCount++; |
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return element; |
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} |
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|
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/** |
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* Unlinks non-null last node l. |
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*/ |
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private E unlinkLast(Node<E> l) { |
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// assert l == last && l != null; |
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final E element = l.item; |
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final Node<E> prev = l.prev; |
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l.item = null; |
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l.prev = null; // help GC |
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last = prev; |
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if (prev == null) |
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first = null; |
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else |
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prev.next = null; |
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size--; |
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modCount++; |
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return element; |
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} |
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|
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/** |
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* Unlinks non-null node x. |
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*/ |
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E unlink(Node<E> x) { |
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// assert x != null; |
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final E element = x.item; |
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final Node<E> next = x.next; |
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final Node<E> prev = x.prev; |
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|
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if (prev == null) { |
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first = next; |
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} else { |
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prev.next = next; |
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x.prev = null; |
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} |
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|
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if (next == null) { |
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last = prev; |
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} else { |
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next.prev = prev; |
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x.next = null; |
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} |
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|
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x.item = null; |
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size--; |
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modCount++; |
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return element; |
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} |
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|
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/** |
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* Returns the first element in this list. |
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* |
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* @return the first element in this list |
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* @throws NoSuchElementException if this list is empty |
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*/ |
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public E getFirst() { |
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final Node<E> f = first; |
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if (f == null) |
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throw new NoSuchElementException(); |
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return f.item; |
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} |
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|
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/** |
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* Returns the last element in this list. |
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* |
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* @return the last element in this list |
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* @throws NoSuchElementException if this list is empty |
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*/ |
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public E getLast() { |
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final Node<E> l = last; |
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if (l == null) |
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throw new NoSuchElementException(); |
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return l.item; |
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} |
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|
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/** |
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* Removes and returns the first element from this list. |
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* |
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* @return the first element from this list |
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* @throws NoSuchElementException if this list is empty |
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*/ |
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public E removeFirst() { |
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final Node<E> f = first; |
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if (f == null) |
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throw new NoSuchElementException(); |
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return unlinkFirst(f); |
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} |
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|
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/** |
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* Removes and returns the last element from this list. |
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* |
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* @return the last element from this list |
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* @throws NoSuchElementException if this list is empty |
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*/ |
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public E removeLast() { |
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final Node<E> l = last; |
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if (l == null) |
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throw new NoSuchElementException(); |
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return unlinkLast(l); |
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} |
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|
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/** |
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* Inserts the specified element at the beginning of this list. |
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* |
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* @param e the element to add |
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*/ |
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public void addFirst(E e) { |
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linkFirst(e); |
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} |
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|
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/** |
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* Appends the specified element to the end of this list. |
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* |
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* <p>This method is equivalent to {@link #add}. |
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* |
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* @param e the element to add |
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*/ |
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public void addLast(E e) { |
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linkLast(e); |
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} |
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|
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/** |
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* Returns {@code true} if this list contains the specified element. |
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* More formally, returns {@code true} if and only if this list contains |
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* at least one element {@code e} such that |
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* <tt>(o==null ? e==null : o.equals(e))</tt>. |
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* |
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* @param o element whose presence in this list is to be tested |
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* @return {@code true} if this list contains the specified element |
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*/ |
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public boolean contains(Object o) { |
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return indexOf(o) != -1; |
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} |
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|
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/** |
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* Returns the number of elements in this list. |
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* |
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* @return the number of elements in this list |
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*/ |
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public int size() { |
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return size; |
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} |
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|
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/** |
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* Appends the specified element to the end of this list. |
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* |
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* <p>This method is equivalent to {@link #addLast}. |
340 |
* |
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* @param e element to be appended to this list |
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* @return {@code true} (as specified by {@link Collection#add}) |
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*/ |
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public boolean add(E e) { |
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linkLast(e); |
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return true; |
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} |
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|
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/** |
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* Removes the first occurrence of the specified element from this list, |
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* if it is present. If this list does not contain the element, it is |
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* unchanged. More formally, removes the element with the lowest index |
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* {@code i} such that |
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* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> |
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* (if such an element exists). Returns {@code true} if this list |
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* contained the specified element (or equivalently, if this list |
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* changed as a result of the call). |
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* |
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* @param o element to be removed from this list, if present |
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* @return {@code true} if this list contained the specified element |
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*/ |
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public boolean remove(Object o) { |
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if (o == null) { |
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for (Node<E> x = first; x != null; x = x.next) { |
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if (x.item == null) { |
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unlink(x); |
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return true; |
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} |
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} |
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} else { |
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for (Node<E> x = first; x != null; x = x.next) { |
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if (o.equals(x.item)) { |
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unlink(x); |
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return true; |
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} |
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} |
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} |
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return false; |
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} |
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|
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/** |
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* Appends all of the elements in the specified collection to the end of |
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* this list, in the order that they are returned by the specified |
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* collection's iterator. The behavior of this operation is undefined if |
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* the specified collection is modified while the operation is in |
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* progress. (Note that this will occur if the specified collection is |
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* this list, and it's nonempty.) |
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* |
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* @param c collection containing elements to be added to this list |
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* @return {@code true} if this list changed as a result of the call |
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* @throws NullPointerException if the specified collection is null |
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*/ |
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public boolean addAll(Collection<? extends E> c) { |
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return addAll(size, c); |
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} |
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|
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/** |
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* Inserts all of the elements in the specified collection into this |
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* list, starting at the specified position. Shifts the element |
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* currently at that position (if any) and any subsequent elements to |
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* the right (increases their indices). The new elements will appear |
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* in the list in the order that they are returned by the |
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* specified collection's iterator. |
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* |
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* @param index index at which to insert the first element |
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* from the specified collection |
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* @param c collection containing elements to be added to this list |
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* @return {@code true} if this list changed as a result of the call |
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* @throws IndexOutOfBoundsException {@inheritDoc} |
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* @throws NullPointerException if the specified collection is null |
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*/ |
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public boolean addAll(int index, Collection<? extends E> c) { |
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checkPositionIndex(index); |
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|
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Object[] a = c.toArray(); |
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int numNew = a.length; |
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if (numNew == 0) |
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return false; |
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|
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Node<E> pred, succ; |
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if (index == size) { |
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succ = null; |
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pred = last; |
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} else { |
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succ = node(index); |
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pred = succ.prev; |
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} |
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|
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for (Object o : a) { |
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@SuppressWarnings("unchecked") E e = (E) o; |
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Node<E> newNode = new Node<E>(pred, e, null); |
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if (pred == null) |
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first = newNode; |
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else |
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pred.next = newNode; |
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pred = newNode; |
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} |
438 |
|
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if (succ == null) { |
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last = pred; |
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} else { |
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pred.next = succ; |
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succ.prev = pred; |
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} |
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|
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size += numNew; |
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modCount++; |
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return true; |
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} |
450 |
|
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/** |
452 |
* Removes all of the elements from this list. |
453 |
* The list will be empty after this call returns. |
454 |
*/ |
455 |
public void clear() { |
456 |
// Clearing all of the links between nodes is "unnecessary", but: |
457 |
// - helps a generational GC if the discarded nodes inhabit |
458 |
// more than one generation |
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// - is sure to free memory even if there is a reachable Iterator |
460 |
for (Node<E> x = first; x != null; ) { |
461 |
Node<E> next = x.next; |
462 |
x.item = null; |
463 |
x.next = null; |
464 |
x.prev = null; |
465 |
x = next; |
466 |
} |
467 |
first = last = null; |
468 |
size = 0; |
469 |
modCount++; |
470 |
} |
471 |
|
472 |
|
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// Positional Access Operations |
474 |
|
475 |
/** |
476 |
* Returns the element at the specified position in this list. |
477 |
* |
478 |
* @param index index of the element to return |
479 |
* @return the element at the specified position in this list |
480 |
* @throws IndexOutOfBoundsException {@inheritDoc} |
481 |
*/ |
482 |
public E get(int index) { |
483 |
checkElementIndex(index); |
484 |
return node(index).item; |
485 |
} |
486 |
|
487 |
/** |
488 |
* Replaces the element at the specified position in this list with the |
489 |
* specified element. |
490 |
* |
491 |
* @param index index of the element to replace |
492 |
* @param element element to be stored at the specified position |
493 |
* @return the element previously at the specified position |
494 |
* @throws IndexOutOfBoundsException {@inheritDoc} |
495 |
*/ |
496 |
public E set(int index, E element) { |
497 |
checkElementIndex(index); |
498 |
Node<E> x = node(index); |
499 |
E oldVal = x.item; |
500 |
x.item = element; |
501 |
return oldVal; |
502 |
} |
503 |
|
504 |
/** |
505 |
* Inserts the specified element at the specified position in this list. |
506 |
* Shifts the element currently at that position (if any) and any |
507 |
* subsequent elements to the right (adds one to their indices). |
508 |
* |
509 |
* @param index index at which the specified element is to be inserted |
510 |
* @param element element to be inserted |
511 |
* @throws IndexOutOfBoundsException {@inheritDoc} |
512 |
*/ |
513 |
public void add(int index, E element) { |
514 |
checkPositionIndex(index); |
515 |
|
516 |
if (index == size) |
517 |
linkLast(element); |
518 |
else |
519 |
linkBefore(element, node(index)); |
520 |
} |
521 |
|
522 |
/** |
523 |
* Removes the element at the specified position in this list. Shifts any |
524 |
* subsequent elements to the left (subtracts one from their indices). |
525 |
* Returns the element that was removed from the list. |
526 |
* |
527 |
* @param index the index of the element to be removed |
528 |
* @return the element previously at the specified position |
529 |
* @throws IndexOutOfBoundsException {@inheritDoc} |
530 |
*/ |
531 |
public E remove(int index) { |
532 |
checkElementIndex(index); |
533 |
return unlink(node(index)); |
534 |
} |
535 |
|
536 |
/** |
537 |
* Tells if the argument is the index of an existing element. |
538 |
*/ |
539 |
private boolean isElementIndex(int index) { |
540 |
return index >= 0 && index < size; |
541 |
} |
542 |
|
543 |
/** |
544 |
* Tells if the argument is the index of a valid position for an |
545 |
* iterator or an add operation. |
546 |
*/ |
547 |
private boolean isPositionIndex(int index) { |
548 |
return index >= 0 && index <= size; |
549 |
} |
550 |
|
551 |
/** |
552 |
* Constructs an IndexOutOfBoundsException detail message. |
553 |
* Of the many possible refactorings of the error handling code, |
554 |
* this "outlining" performs best with both server and client VMs. |
555 |
*/ |
556 |
private String outOfBoundsMsg(int index) { |
557 |
return "Index: "+index+", Size: "+size; |
558 |
} |
559 |
|
560 |
private void checkElementIndex(int index) { |
561 |
if (!isElementIndex(index)) |
562 |
throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); |
563 |
} |
564 |
|
565 |
private void checkPositionIndex(int index) { |
566 |
if (!isPositionIndex(index)) |
567 |
throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); |
568 |
} |
569 |
|
570 |
/** |
571 |
* Returns the (non-null) Node at the specified element index. |
572 |
*/ |
573 |
Node<E> node(int index) { |
574 |
// assert isElementIndex(index); |
575 |
|
576 |
if (index < (size >> 1)) { |
577 |
Node<E> x = first; |
578 |
for (int i = 0; i < index; i++) |
579 |
x = x.next; |
580 |
return x; |
581 |
} else { |
582 |
Node<E> x = last; |
583 |
for (int i = size - 1; i > index; i--) |
584 |
x = x.prev; |
585 |
return x; |
586 |
} |
587 |
} |
588 |
|
589 |
// Search Operations |
590 |
|
591 |
/** |
592 |
* Returns the index of the first occurrence of the specified element |
593 |
* in this list, or -1 if this list does not contain the element. |
594 |
* More formally, returns the lowest index {@code i} such that |
595 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, |
596 |
* or -1 if there is no such index. |
597 |
* |
598 |
* @param o element to search for |
599 |
* @return the index of the first occurrence of the specified element in |
600 |
* this list, or -1 if this list does not contain the element |
601 |
*/ |
602 |
public int indexOf(Object o) { |
603 |
int index = 0; |
604 |
if (o == null) { |
605 |
for (Node<E> x = first; x != null; x = x.next) { |
606 |
if (x.item == null) |
607 |
return index; |
608 |
index++; |
609 |
} |
610 |
} else { |
611 |
for (Node<E> x = first; x != null; x = x.next) { |
612 |
if (o.equals(x.item)) |
613 |
return index; |
614 |
index++; |
615 |
} |
616 |
} |
617 |
return -1; |
618 |
} |
619 |
|
620 |
/** |
621 |
* Returns the index of the last occurrence of the specified element |
622 |
* in this list, or -1 if this list does not contain the element. |
623 |
* More formally, returns the highest index {@code i} such that |
624 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, |
625 |
* or -1 if there is no such index. |
626 |
* |
627 |
* @param o element to search for |
628 |
* @return the index of the last occurrence of the specified element in |
629 |
* this list, or -1 if this list does not contain the element |
630 |
*/ |
631 |
public int lastIndexOf(Object o) { |
632 |
int index = size; |
633 |
if (o == null) { |
634 |
for (Node<E> x = last; x != null; x = x.prev) { |
635 |
index--; |
636 |
if (x.item == null) |
637 |
return index; |
638 |
} |
639 |
} else { |
640 |
for (Node<E> x = last; x != null; x = x.prev) { |
641 |
index--; |
642 |
if (o.equals(x.item)) |
643 |
return index; |
644 |
} |
645 |
} |
646 |
return -1; |
647 |
} |
648 |
|
649 |
// Queue operations. |
650 |
|
651 |
/** |
652 |
* Retrieves, but does not remove, the head (first element) of this list. |
653 |
* |
654 |
* @return the head of this list, or {@code null} if this list is empty |
655 |
* @since 1.5 |
656 |
*/ |
657 |
public E peek() { |
658 |
final Node<E> f = first; |
659 |
return (f == null) ? null : f.item; |
660 |
} |
661 |
|
662 |
/** |
663 |
* Retrieves, but does not remove, the head (first element) of this list. |
664 |
* |
665 |
* @return the head of this list |
666 |
* @throws NoSuchElementException if this list is empty |
667 |
* @since 1.5 |
668 |
*/ |
669 |
public E element() { |
670 |
return getFirst(); |
671 |
} |
672 |
|
673 |
/** |
674 |
* Retrieves and removes the head (first element) of this list. |
675 |
* |
676 |
* @return the head of this list, or {@code null} if this list is empty |
677 |
* @since 1.5 |
678 |
*/ |
679 |
public E poll() { |
680 |
final Node<E> f = first; |
681 |
return (f == null) ? null : unlinkFirst(f); |
682 |
} |
683 |
|
684 |
/** |
685 |
* Retrieves and removes the head (first element) of this list. |
686 |
* |
687 |
* @return the head of this list |
688 |
* @throws NoSuchElementException if this list is empty |
689 |
* @since 1.5 |
690 |
*/ |
691 |
public E remove() { |
692 |
return removeFirst(); |
693 |
} |
694 |
|
695 |
/** |
696 |
* Adds the specified element as the tail (last element) of this list. |
697 |
* |
698 |
* @param e the element to add |
699 |
* @return {@code true} (as specified by {@link Queue#offer}) |
700 |
* @since 1.5 |
701 |
*/ |
702 |
public boolean offer(E e) { |
703 |
return add(e); |
704 |
} |
705 |
|
706 |
// Deque operations |
707 |
/** |
708 |
* Inserts the specified element at the front of this list. |
709 |
* |
710 |
* @param e the element to insert |
711 |
* @return {@code true} (as specified by {@link Deque#offerFirst}) |
712 |
* @since 1.6 |
713 |
*/ |
714 |
public boolean offerFirst(E e) { |
715 |
addFirst(e); |
716 |
return true; |
717 |
} |
718 |
|
719 |
/** |
720 |
* Inserts the specified element at the end of this list. |
721 |
* |
722 |
* @param e the element to insert |
723 |
* @return {@code true} (as specified by {@link Deque#offerLast}) |
724 |
* @since 1.6 |
725 |
*/ |
726 |
public boolean offerLast(E e) { |
727 |
addLast(e); |
728 |
return true; |
729 |
} |
730 |
|
731 |
/** |
732 |
* Retrieves, but does not remove, the first element of this list, |
733 |
* or returns {@code null} if this list is empty. |
734 |
* |
735 |
* @return the first element of this list, or {@code null} |
736 |
* if this list is empty |
737 |
* @since 1.6 |
738 |
*/ |
739 |
public E peekFirst() { |
740 |
final Node<E> f = first; |
741 |
return (f == null) ? null : f.item; |
742 |
} |
743 |
|
744 |
/** |
745 |
* Retrieves, but does not remove, the last element of this list, |
746 |
* or returns {@code null} if this list is empty. |
747 |
* |
748 |
* @return the last element of this list, or {@code null} |
749 |
* if this list is empty |
750 |
* @since 1.6 |
751 |
*/ |
752 |
public E peekLast() { |
753 |
final Node<E> l = last; |
754 |
return (l == null) ? null : l.item; |
755 |
} |
756 |
|
757 |
/** |
758 |
* Retrieves and removes the first element of this list, |
759 |
* or returns {@code null} if this list is empty. |
760 |
* |
761 |
* @return the first element of this list, or {@code null} if |
762 |
* this list is empty |
763 |
* @since 1.6 |
764 |
*/ |
765 |
public E pollFirst() { |
766 |
final Node<E> f = first; |
767 |
return (f == null) ? null : unlinkFirst(f); |
768 |
} |
769 |
|
770 |
/** |
771 |
* Retrieves and removes the last element of this list, |
772 |
* or returns {@code null} if this list is empty. |
773 |
* |
774 |
* @return the last element of this list, or {@code null} if |
775 |
* this list is empty |
776 |
* @since 1.6 |
777 |
*/ |
778 |
public E pollLast() { |
779 |
final Node<E> l = last; |
780 |
return (l == null) ? null : unlinkLast(l); |
781 |
} |
782 |
|
783 |
/** |
784 |
* Pushes an element onto the stack represented by this list. In other |
785 |
* words, inserts the element at the front of this list. |
786 |
* |
787 |
* <p>This method is equivalent to {@link #addFirst}. |
788 |
* |
789 |
* @param e the element to push |
790 |
* @since 1.6 |
791 |
*/ |
792 |
public void push(E e) { |
793 |
addFirst(e); |
794 |
} |
795 |
|
796 |
/** |
797 |
* Pops an element from the stack represented by this list. In other |
798 |
* words, removes and returns the first element of this list. |
799 |
* |
800 |
* <p>This method is equivalent to {@link #removeFirst()}. |
801 |
* |
802 |
* @return the element at the front of this list (which is the top |
803 |
* of the stack represented by this list) |
804 |
* @throws NoSuchElementException if this list is empty |
805 |
* @since 1.6 |
806 |
*/ |
807 |
public E pop() { |
808 |
return removeFirst(); |
809 |
} |
810 |
|
811 |
/** |
812 |
* Removes the first occurrence of the specified element in this |
813 |
* list (when traversing the list from head to tail). If the list |
814 |
* does not contain the element, it is unchanged. |
815 |
* |
816 |
* @param o element to be removed from this list, if present |
817 |
* @return {@code true} if the list contained the specified element |
818 |
* @since 1.6 |
819 |
*/ |
820 |
public boolean removeFirstOccurrence(Object o) { |
821 |
return remove(o); |
822 |
} |
823 |
|
824 |
/** |
825 |
* Removes the last occurrence of the specified element in this |
826 |
* list (when traversing the list from head to tail). If the list |
827 |
* does not contain the element, it is unchanged. |
828 |
* |
829 |
* @param o element to be removed from this list, if present |
830 |
* @return {@code true} if the list contained the specified element |
831 |
* @since 1.6 |
832 |
*/ |
833 |
public boolean removeLastOccurrence(Object o) { |
834 |
if (o == null) { |
835 |
for (Node<E> x = last; x != null; x = x.prev) { |
836 |
if (x.item == null) { |
837 |
unlink(x); |
838 |
return true; |
839 |
} |
840 |
} |
841 |
} else { |
842 |
for (Node<E> x = last; x != null; x = x.prev) { |
843 |
if (o.equals(x.item)) { |
844 |
unlink(x); |
845 |
return true; |
846 |
} |
847 |
} |
848 |
} |
849 |
return false; |
850 |
} |
851 |
|
852 |
/** |
853 |
* Returns a list-iterator of the elements in this list (in proper |
854 |
* sequence), starting at the specified position in the list. |
855 |
* Obeys the general contract of {@code List.listIterator(int)}.<p> |
856 |
* |
857 |
* The list-iterator is <i>fail-fast</i>: if the list is structurally |
858 |
* modified at any time after the Iterator is created, in any way except |
859 |
* through the list-iterator's own {@code remove} or {@code add} |
860 |
* methods, the list-iterator will throw a |
861 |
* {@code ConcurrentModificationException}. Thus, in the face of |
862 |
* concurrent modification, the iterator fails quickly and cleanly, rather |
863 |
* than risking arbitrary, non-deterministic behavior at an undetermined |
864 |
* time in the future. |
865 |
* |
866 |
* @param index index of the first element to be returned from the |
867 |
* list-iterator (by a call to {@code next}) |
868 |
* @return a ListIterator of the elements in this list (in proper |
869 |
* sequence), starting at the specified position in the list |
870 |
* @throws IndexOutOfBoundsException {@inheritDoc} |
871 |
* @see List#listIterator(int) |
872 |
*/ |
873 |
public ListIterator<E> listIterator(int index) { |
874 |
checkPositionIndex(index); |
875 |
return new ListItr(index); |
876 |
} |
877 |
|
878 |
private class ListItr implements ListIterator<E> { |
879 |
private Node<E> lastReturned = null; |
880 |
private Node<E> next; |
881 |
private int nextIndex; |
882 |
private int expectedModCount = modCount; |
883 |
|
884 |
ListItr(int index) { |
885 |
// assert isPositionIndex(index); |
886 |
next = (index == size) ? null : node(index); |
887 |
nextIndex = index; |
888 |
} |
889 |
|
890 |
public boolean hasNext() { |
891 |
return nextIndex < size; |
892 |
} |
893 |
|
894 |
public E next() { |
895 |
checkForComodification(); |
896 |
if (!hasNext()) |
897 |
throw new NoSuchElementException(); |
898 |
|
899 |
lastReturned = next; |
900 |
next = next.next; |
901 |
nextIndex++; |
902 |
return lastReturned.item; |
903 |
} |
904 |
|
905 |
public boolean hasPrevious() { |
906 |
return nextIndex > 0; |
907 |
} |
908 |
|
909 |
public E previous() { |
910 |
checkForComodification(); |
911 |
if (!hasPrevious()) |
912 |
throw new NoSuchElementException(); |
913 |
|
914 |
lastReturned = next = (next == null) ? last : next.prev; |
915 |
nextIndex--; |
916 |
return lastReturned.item; |
917 |
} |
918 |
|
919 |
public int nextIndex() { |
920 |
return nextIndex; |
921 |
} |
922 |
|
923 |
public int previousIndex() { |
924 |
return nextIndex - 1; |
925 |
} |
926 |
|
927 |
public void remove() { |
928 |
checkForComodification(); |
929 |
if (lastReturned == null) |
930 |
throw new IllegalStateException(); |
931 |
|
932 |
Node<E> lastNext = lastReturned.next; |
933 |
unlink(lastReturned); |
934 |
if (next == lastReturned) |
935 |
next = lastNext; |
936 |
else |
937 |
nextIndex--; |
938 |
lastReturned = null; |
939 |
expectedModCount++; |
940 |
} |
941 |
|
942 |
public void set(E e) { |
943 |
if (lastReturned == null) |
944 |
throw new IllegalStateException(); |
945 |
checkForComodification(); |
946 |
lastReturned.item = e; |
947 |
} |
948 |
|
949 |
public void add(E e) { |
950 |
checkForComodification(); |
951 |
lastReturned = null; |
952 |
if (next == null) |
953 |
linkLast(e); |
954 |
else |
955 |
linkBefore(e, next); |
956 |
nextIndex++; |
957 |
expectedModCount++; |
958 |
} |
959 |
|
960 |
final void checkForComodification() { |
961 |
if (modCount != expectedModCount) |
962 |
throw new ConcurrentModificationException(); |
963 |
} |
964 |
} |
965 |
|
966 |
private static class Node<E> { |
967 |
E item; |
968 |
Node<E> next; |
969 |
Node<E> prev; |
970 |
|
971 |
Node(Node<E> prev, E element, Node<E> next) { |
972 |
this.item = element; |
973 |
this.next = next; |
974 |
this.prev = prev; |
975 |
} |
976 |
} |
977 |
|
978 |
/** |
979 |
* @since 1.6 |
980 |
*/ |
981 |
public Iterator<E> descendingIterator() { |
982 |
return new DescendingIterator(); |
983 |
} |
984 |
|
985 |
/** |
986 |
* Adapter to provide descending iterators via ListItr.previous |
987 |
*/ |
988 |
private class DescendingIterator implements Iterator<E> { |
989 |
private final ListItr itr = new ListItr(size()); |
990 |
public boolean hasNext() { |
991 |
return itr.hasPrevious(); |
992 |
} |
993 |
public E next() { |
994 |
return itr.previous(); |
995 |
} |
996 |
public void remove() { |
997 |
itr.remove(); |
998 |
} |
999 |
} |
1000 |
|
1001 |
@SuppressWarnings("unchecked") |
1002 |
private LinkedList<E> superClone() { |
1003 |
try { |
1004 |
return (LinkedList<E>) super.clone(); |
1005 |
} catch (CloneNotSupportedException e) { |
1006 |
throw new InternalError(); |
1007 |
} |
1008 |
} |
1009 |
|
1010 |
/** |
1011 |
* Returns a shallow copy of this {@code LinkedList}. (The elements |
1012 |
* themselves are not cloned.) |
1013 |
* |
1014 |
* @return a shallow copy of this {@code LinkedList} instance |
1015 |
*/ |
1016 |
public Object clone() { |
1017 |
LinkedList<E> clone = superClone(); |
1018 |
|
1019 |
// Put clone into "virgin" state |
1020 |
clone.first = clone.last = null; |
1021 |
clone.size = 0; |
1022 |
clone.modCount = 0; |
1023 |
|
1024 |
// Initialize clone with our elements |
1025 |
for (Node<E> x = first; x != null; x = x.next) |
1026 |
clone.add(x.item); |
1027 |
|
1028 |
return clone; |
1029 |
} |
1030 |
|
1031 |
/** |
1032 |
* Returns an array containing all of the elements in this list |
1033 |
* in proper sequence (from first to last element). |
1034 |
* |
1035 |
* <p>The returned array will be "safe" in that no references to it are |
1036 |
* maintained by this list. (In other words, this method must allocate |
1037 |
* a new array). The caller is thus free to modify the returned array. |
1038 |
* |
1039 |
* <p>This method acts as bridge between array-based and collection-based |
1040 |
* APIs. |
1041 |
* |
1042 |
* @return an array containing all of the elements in this list |
1043 |
* in proper sequence |
1044 |
*/ |
1045 |
public Object[] toArray() { |
1046 |
Object[] result = new Object[size]; |
1047 |
int i = 0; |
1048 |
for (Node<E> x = first; x != null; x = x.next) |
1049 |
result[i++] = x.item; |
1050 |
return result; |
1051 |
} |
1052 |
|
1053 |
/** |
1054 |
* Returns an array containing all of the elements in this list in |
1055 |
* proper sequence (from first to last element); the runtime type of |
1056 |
* the returned array is that of the specified array. If the list fits |
1057 |
* in the specified array, it is returned therein. Otherwise, a new |
1058 |
* array is allocated with the runtime type of the specified array and |
1059 |
* the size of this list. |
1060 |
* |
1061 |
* <p>If the list fits in the specified array with room to spare (i.e., |
1062 |
* the array has more elements than the list), the element in the array |
1063 |
* immediately following the end of the list is set to {@code null}. |
1064 |
* (This is useful in determining the length of the list <i>only</i> if |
1065 |
* the caller knows that the list does not contain any null elements.) |
1066 |
* |
1067 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
1068 |
* array-based and collection-based APIs. Further, this method allows |
1069 |
* precise control over the runtime type of the output array, and may, |
1070 |
* under certain circumstances, be used to save allocation costs. |
1071 |
* |
1072 |
* <p>Suppose {@code x} is a list known to contain only strings. |
1073 |
* The following code can be used to dump the list into a newly |
1074 |
* allocated array of {@code String}: |
1075 |
* |
1076 |
* <pre> |
1077 |
* String[] y = x.toArray(new String[0]);</pre> |
1078 |
* |
1079 |
* Note that {@code toArray(new Object[0])} is identical in function to |
1080 |
* {@code toArray()}. |
1081 |
* |
1082 |
* @param a the array into which the elements of the list are to |
1083 |
* be stored, if it is big enough; otherwise, a new array of the |
1084 |
* same runtime type is allocated for this purpose. |
1085 |
* @return an array containing the elements of the list |
1086 |
* @throws ArrayStoreException if the runtime type of the specified array |
1087 |
* is not a supertype of the runtime type of every element in |
1088 |
* this list |
1089 |
* @throws NullPointerException if the specified array is null |
1090 |
*/ |
1091 |
@SuppressWarnings("unchecked") |
1092 |
public <T> T[] toArray(T[] a) { |
1093 |
if (a.length < size) |
1094 |
a = (T[])java.lang.reflect.Array.newInstance( |
1095 |
a.getClass().getComponentType(), size); |
1096 |
int i = 0; |
1097 |
Object[] result = a; |
1098 |
for (Node<E> x = first; x != null; x = x.next) |
1099 |
result[i++] = x.item; |
1100 |
|
1101 |
if (a.length > size) |
1102 |
a[size] = null; |
1103 |
|
1104 |
return a; |
1105 |
} |
1106 |
|
1107 |
private static final long serialVersionUID = 876323262645176354L; |
1108 |
|
1109 |
/** |
1110 |
* Saves the state of this {@code LinkedList} instance to a stream |
1111 |
* (that is, serializes it). |
1112 |
* |
1113 |
* @serialData The size of the list (the number of elements it |
1114 |
* contains) is emitted (int), followed by all of its |
1115 |
* elements (each an Object) in the proper order. |
1116 |
*/ |
1117 |
private void writeObject(java.io.ObjectOutputStream s) |
1118 |
throws java.io.IOException { |
1119 |
// Write out any hidden serialization magic |
1120 |
s.defaultWriteObject(); |
1121 |
|
1122 |
// Write out size |
1123 |
s.writeInt(size); |
1124 |
|
1125 |
// Write out all elements in the proper order. |
1126 |
for (Node<E> x = first; x != null; x = x.next) |
1127 |
s.writeObject(x.item); |
1128 |
} |
1129 |
|
1130 |
/** |
1131 |
* Reconstitutes this {@code LinkedList} instance from a stream |
1132 |
* (that is, deserializes it). |
1133 |
*/ |
1134 |
@SuppressWarnings("unchecked") |
1135 |
private void readObject(java.io.ObjectInputStream s) |
1136 |
throws java.io.IOException, ClassNotFoundException { |
1137 |
// Read in any hidden serialization magic |
1138 |
s.defaultReadObject(); |
1139 |
|
1140 |
// Read in size |
1141 |
int size = s.readInt(); |
1142 |
|
1143 |
// Read in all elements in the proper order. |
1144 |
for (int i = 0; i < size; i++) |
1145 |
linkLast((E)s.readObject()); |
1146 |
} |
1147 |
} |