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/* |
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* %W% %E% |
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* |
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* Copyright 2004 Sun Microsystems, Inc. All rights reserved. |
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* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. |
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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 <tt>List</tt> interface. Implements all |
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* optional list operations, and permits all elements (including |
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* <tt>null</tt>). In addition to implementing the <tt>List</tt> interface, |
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* the <tt>LinkedList</tt> class provides uniformly named methods to |
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* <tt>get</tt>, <tt>remove</tt> and <tt>insert</tt> 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, queue, or double-ended queue ({@link Deque}).<p> |
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* |
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* The class implements the <tt>Deque</tt> interface, providing |
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* first-in-first-out queue operations for <tt>add</tt>, |
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* <tt>poll</tt>, along with other stack and deque operations. |
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* |
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* 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.<p> |
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* |
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* <b>Note that this implementation is not synchronized.</b> If multiple |
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* threads access a list concurrently, and at least one of the threads |
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* modifies the list structurally, it <i>must</i> be synchronized |
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* externally. (A structural modification is any operation that adds or |
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* deletes one or more elements; merely setting the value of an element is not |
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* a structural modification.) This is typically accomplished by |
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* synchronizing on some object that naturally encapsulates the list. If no |
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* such object exists, the list should be "wrapped" using the |
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* Collections.synchronizedList method. This is best done at creation time, |
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* to prevent accidental unsynchronized access to the list: <pre> |
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* List list = Collections.synchronizedList(new LinkedList(...)); |
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* </pre><p> |
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* |
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* The iterators returned by the this class's <tt>iterator</tt> and |
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* <tt>listIterator</tt> 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 any way |
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* except through the Iterator's own <tt>remove</tt> or <tt>add</tt> methods, |
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* the iterator will throw a <tt>ConcurrentModificationException</tt>. Thus, |
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* in the face of concurrent modification, the iterator fails quickly and |
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* cleanly, rather than risking arbitrary, non-deterministic behavior at an |
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* undetermined 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 <tt>ConcurrentModificationException</tt> 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><p> |
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* |
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* This class is a member of the |
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* <a href="{@docRoot}/../guide/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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* @version %I%, %G% |
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* @see List |
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* @see ArrayList |
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* @see Vector |
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* @see Collections#synchronizedList(List) |
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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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private transient Entry<E> header = new Entry<E>(null, null, null); |
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private transient int size = 0; |
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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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header.next = header.previous = header; |
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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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* 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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if (size==0) |
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throw new NoSuchElementException(); |
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|
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return header.next.element; |
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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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if (size==0) |
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throw new NoSuchElementException(); |
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|
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return header.previous.element; |
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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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return remove(header.next); |
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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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return remove(header.previous); |
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} |
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|
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/** |
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* Inserts the given element at the beginning of this list. |
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* |
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* @param o the element to be inserted at the beginning of this list. |
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*/ |
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public void addFirst(E o) { |
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addBefore(o, header.next); |
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} |
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|
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/** |
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* Appends the given element to the end of this list. (Identical in |
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* function to the <tt>add</tt> method; included only for consistency.) |
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* |
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* @param o the element to be inserted at the end of this list. |
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*/ |
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public void addLast(E o) { |
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addBefore(o, header); |
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} |
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|
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/** |
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* Returns <tt>true</tt> if this list contains the specified element. |
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* More formally, returns <tt>true</tt> if and only if this list contains |
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* at least one element <tt>e</tt> such that <tt>(o==null ? e==null |
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* : 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 <tt>true</tt> 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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* @param o element to be appended to this list. |
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* @return <tt>true</tt> (as per the general contract of |
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* <tt>Collection.add</tt>). |
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*/ |
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public boolean add(E o) { |
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addBefore(o, header); |
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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 in this list. If |
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* the list does not contain the element, it is unchanged. More formally, |
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* removes the element with the lowest index <tt>i</tt> such that |
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* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> (if such an |
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* element exists). |
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* |
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* @param o element to be removed from this list, if present. |
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* @return <tt>true</tt> if the 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 (Entry<E> e = header.next; e != header; e = e.next) { |
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if (e.element==null) { |
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remove(e); |
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return true; |
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} |
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} |
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} else { |
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for (Entry<E> e = header.next; e != header; e = e.next) { |
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if (o.equals(e.element)) { |
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remove(e); |
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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. (This implies that the behavior of this call is undefined if |
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* the specified Collection is this list, and this list is nonempty.) |
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* |
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* @param c the elements to be inserted into this list. |
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* @return <tt>true</tt> 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 first element |
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* from the specified collection. |
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* @param c elements to be inserted into this list. |
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* @return <tt>true</tt> if this list changed as a result of the call. |
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* @throws IndexOutOfBoundsException if the specified index is out of |
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* range (<tt>index < 0 || index > size()</tt>). |
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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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if (index < 0 || index > size) |
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throw new IndexOutOfBoundsException("Index: "+index+ |
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", Size: "+size); |
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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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modCount++; |
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|
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Entry<E> successor = (index==size ? header : entry(index)); |
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Entry<E> predecessor = successor.previous; |
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for (int i=0; i<numNew; i++) { |
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Entry<E> e = new Entry<E>((E)a[i], successor, predecessor); |
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predecessor.next = e; |
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predecessor = e; |
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} |
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successor.previous = predecessor; |
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|
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size += numNew; |
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return true; |
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} |
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|
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/** |
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* Removes all of the elements from this list. |
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*/ |
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public void clear() { |
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Entry<E> e = header.next; |
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while (e != header) { |
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Entry<E> next = e.next; |
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e.next = e.previous = null; |
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e.element = null; |
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e = next; |
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} |
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header.next = header.previous = header; |
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size = 0; |
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modCount++; |
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} |
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|
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|
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// Positional Access Operations |
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|
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/** |
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* Returns the element at the specified position in this list. |
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* |
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* @param index index of element to return. |
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* @return the element at the specified position in this list. |
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* |
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* @throws IndexOutOfBoundsException if the specified index is out of |
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* range (<tt>index < 0 || index >= size()</tt>). |
308 |
*/ |
309 |
public E get(int index) { |
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return entry(index).element; |
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} |
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|
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/** |
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* Replaces the element at the specified position in this list with the |
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* specified element. |
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* |
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* @param index index of element to replace. |
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* @param element element to be stored at the specified position. |
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* @return the element previously at the specified position. |
320 |
* @throws IndexOutOfBoundsException if the specified index is out of |
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* range (<tt>index < 0 || index >= size()</tt>). |
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*/ |
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public E set(int index, E element) { |
324 |
Entry<E> e = entry(index); |
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E oldVal = e.element; |
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e.element = element; |
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return oldVal; |
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} |
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|
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/** |
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* Inserts the specified element at the specified position in this list. |
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* Shifts the element currently at that position (if any) and any |
333 |
* subsequent elements to the right (adds one to their indices). |
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* |
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* @param index index at which the specified element is to be inserted. |
336 |
* @param element element to be inserted. |
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* |
338 |
* @throws IndexOutOfBoundsException if the specified index is out of |
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* range (<tt>index < 0 || index > size()</tt>). |
340 |
*/ |
341 |
public void add(int index, E element) { |
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addBefore(element, (index==size ? header : entry(index))); |
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} |
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|
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/** |
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* Removes the element at the specified position in this list. Shifts any |
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* subsequent elements to the left (subtracts one from their indices). |
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* Returns the element that was removed from the list. |
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* |
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* @param index the index of the element to removed. |
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* @return the element previously at the specified position. |
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* |
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* @throws IndexOutOfBoundsException if the specified index is out of |
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* range (<tt>index < 0 || index >= size()</tt>). |
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*/ |
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public E remove(int index) { |
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return remove(entry(index)); |
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} |
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|
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/** |
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* Return the indexed entry. |
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*/ |
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private Entry<E> entry(int index) { |
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if (index < 0 || index >= size) |
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throw new IndexOutOfBoundsException("Index: "+index+ |
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", Size: "+size); |
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Entry<E> e = header; |
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if (index < (size >> 1)) { |
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for (int i = 0; i <= index; i++) |
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e = e.next; |
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} else { |
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for (int i = size; i > index; i--) |
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e = e.previous; |
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} |
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return e; |
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} |
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|
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|
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// Search Operations |
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|
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/** |
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* Returns the index in this list of the first occurrence of the |
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* specified element, or -1 if the List does not contain this |
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* element. More formally, returns the lowest index i such that |
385 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, or -1 if |
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* there is no such index. |
387 |
* |
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* @param o element to search for. |
389 |
* @return the index in this list of the first occurrence of the |
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* specified element, or -1 if the list does not contain this |
391 |
* element. |
392 |
*/ |
393 |
public int indexOf(Object o) { |
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int index = 0; |
395 |
if (o==null) { |
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for (Entry e = header.next; e != header; e = e.next) { |
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if (e.element==null) |
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return index; |
399 |
index++; |
400 |
} |
401 |
} else { |
402 |
for (Entry e = header.next; e != header; e = e.next) { |
403 |
if (o.equals(e.element)) |
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return index; |
405 |
index++; |
406 |
} |
407 |
} |
408 |
return -1; |
409 |
} |
410 |
|
411 |
/** |
412 |
* Returns the index in this list of the last occurrence of the |
413 |
* specified element, or -1 if the list does not contain this |
414 |
* element. More formally, returns the highest index i such that |
415 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, or -1 if |
416 |
* there is no such index. |
417 |
* |
418 |
* @param o element to search for. |
419 |
* @return the index in this list of the last occurrence of the |
420 |
* specified element, or -1 if the list does not contain this |
421 |
* element. |
422 |
*/ |
423 |
public int lastIndexOf(Object o) { |
424 |
int index = size; |
425 |
if (o==null) { |
426 |
for (Entry e = header.previous; e != header; e = e.previous) { |
427 |
index--; |
428 |
if (e.element==null) |
429 |
return index; |
430 |
} |
431 |
} else { |
432 |
for (Entry e = header.previous; e != header; e = e.previous) { |
433 |
index--; |
434 |
if (o.equals(e.element)) |
435 |
return index; |
436 |
} |
437 |
} |
438 |
return -1; |
439 |
} |
440 |
|
441 |
// Queue operations. |
442 |
|
443 |
/** |
444 |
* Retrieves, but does not remove, the head (first element) of this list. |
445 |
* @return the head of this queue, or <tt>null</tt> if this queue is empty. |
446 |
* @since 1.5 |
447 |
*/ |
448 |
public E peek() { |
449 |
if (size==0) |
450 |
return null; |
451 |
return getFirst(); |
452 |
} |
453 |
|
454 |
/** |
455 |
* Retrieves, but does not remove, the head (first element) of this list. |
456 |
* @return the head of this queue. |
457 |
* @throws NoSuchElementException if this queue is empty. |
458 |
* @since 1.5 |
459 |
*/ |
460 |
public E element() { |
461 |
return getFirst(); |
462 |
} |
463 |
|
464 |
/** |
465 |
* Retrieves and removes the head (first element) of this list. |
466 |
* @return the head of this queue, or <tt>null</tt> if this queue is empty. |
467 |
* @since 1.5 |
468 |
*/ |
469 |
public E poll() { |
470 |
if (size==0) |
471 |
return null; |
472 |
return removeFirst(); |
473 |
} |
474 |
|
475 |
/** |
476 |
* Retrieves and removes the head (first element) of this list. |
477 |
* @return the head of this queue. |
478 |
* @throws NoSuchElementException if this queue is empty. |
479 |
* @since 1.5 |
480 |
*/ |
481 |
public E remove() { |
482 |
return removeFirst(); |
483 |
} |
484 |
|
485 |
/** |
486 |
* Adds the specified element as the tail (last element) of this list. |
487 |
* |
488 |
* @param o the element to add. |
489 |
* @return <tt>true</tt> (as per the general contract of |
490 |
* <tt>Queue.offer</tt>) |
491 |
* @since 1.5 |
492 |
*/ |
493 |
public boolean offer(E o) { |
494 |
return add(o); |
495 |
} |
496 |
|
497 |
// Deque operations |
498 |
/** |
499 |
* Inserts the specified element to the front this deque. |
500 |
* |
501 |
* @param e the element to insert |
502 |
* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst}) |
503 |
* @since 1.6 |
504 |
*/ |
505 |
public boolean offerFirst(E e) { |
506 |
addFirst(e); |
507 |
return true; |
508 |
} |
509 |
|
510 |
/** |
511 |
* Inserts the specified element to the end this deque. |
512 |
* |
513 |
* @param e the element to insert |
514 |
* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast}) |
515 |
* @since 1.6 |
516 |
*/ |
517 |
public boolean offerLast(E e) { |
518 |
addLast(e); |
519 |
return true; |
520 |
} |
521 |
|
522 |
/** |
523 |
* Retrieves, but does not remove, the first element of this deque, |
524 |
* returning <tt>null</tt> if this deque is empty. |
525 |
* |
526 |
* @return the first element of this deque, or <tt>null</tt> if |
527 |
* this deque is empty |
528 |
* @since 1.6 |
529 |
*/ |
530 |
public E peekFirst() { |
531 |
if (size==0) |
532 |
return null; |
533 |
return getFirst(); |
534 |
} |
535 |
|
536 |
/** |
537 |
* Retrieves, but does not remove, the last element of this deque, |
538 |
* returning <tt>null</tt> if this deque is empty. |
539 |
* |
540 |
* @return the last element of this deque, or <tt>null</tt> if this deque |
541 |
* is empty |
542 |
* @since 1.6 |
543 |
*/ |
544 |
public E peekLast() { |
545 |
if (size==0) |
546 |
return null; |
547 |
return getLast(); |
548 |
} |
549 |
|
550 |
/** |
551 |
* Retrieves and removes the first element of this deque, or |
552 |
* <tt>null</tt> if this deque is empty. |
553 |
* |
554 |
* @return the first element of this deque, or <tt>null</tt> if |
555 |
* this deque is empty |
556 |
* @since 1.6 |
557 |
*/ |
558 |
public E pollFirst() { |
559 |
if (size==0) |
560 |
return null; |
561 |
return removeFirst(); |
562 |
} |
563 |
|
564 |
/** |
565 |
* Retrieves and removes the last element of this deque, or |
566 |
* <tt>null</tt> if this deque is empty. |
567 |
* |
568 |
* @return the last element of this deque, or <tt>null</tt> if |
569 |
* this deque is empty |
570 |
* @since 1.6 |
571 |
*/ |
572 |
public E pollLast() { |
573 |
if (size==0) |
574 |
return null; |
575 |
return removeLast(); |
576 |
} |
577 |
|
578 |
/** |
579 |
* Pushes an element onto the stack represented by this deque. In other |
580 |
* words, inserts the element to the front this deque. |
581 |
* |
582 |
* <p>This method is equivalent to {@link #addFirst}. |
583 |
* |
584 |
* @param e the element to push |
585 |
* @since 1.6 |
586 |
*/ |
587 |
public void push(E e) { |
588 |
addFirst(e); |
589 |
} |
590 |
|
591 |
/** |
592 |
* Pops an element from the stack represented by this deque. In other |
593 |
* words, removes and returns the the first element of this deque. |
594 |
* |
595 |
* <p>This method is equivalent to {@link #removeFirst()}. |
596 |
* |
597 |
* @return the element at the front of this deque (which is the top |
598 |
* of the stack represented by this deque) |
599 |
* @throws NoSuchElementException if this deque is empty |
600 |
* @since 1.6 |
601 |
*/ |
602 |
public E pop() { |
603 |
return removeFirst(); |
604 |
} |
605 |
|
606 |
/** |
607 |
* Removes the first occurrence of the specified element in this |
608 |
* deque (when traversing the deque from head to tail). If the deque |
609 |
* does not contain the element, it is unchanged. |
610 |
* |
611 |
* @param e element to be removed from this deque, if present |
612 |
* @return <tt>true</tt> if the deque contained the specified element |
613 |
* @since 1.6 |
614 |
*/ |
615 |
public boolean removeFirstOccurrence(Object e) { |
616 |
return remove(e); |
617 |
} |
618 |
|
619 |
/** |
620 |
* Removes the last occurrence of the specified element in this |
621 |
* deque (when traversing the deque from head to tail). If the deque |
622 |
* does not contain the element, it is unchanged. |
623 |
* |
624 |
* @param o element to be removed from this deque, if present |
625 |
* @return <tt>true</tt> if the deque contained the specified element |
626 |
* @since 1.6 |
627 |
*/ |
628 |
public boolean removeLastOccurrence(Object o) { |
629 |
if (o==null) { |
630 |
for (Entry e = header.previous; e != header; e = e.previous) { |
631 |
if (e.element==null) { |
632 |
remove(e); |
633 |
return true; |
634 |
} |
635 |
} |
636 |
} else { |
637 |
for (Entry e = header.previous; e != header; e = e.previous) { |
638 |
if (o.equals(e.element)) { |
639 |
remove(e); |
640 |
return true; |
641 |
} |
642 |
} |
643 |
} |
644 |
return false; |
645 |
} |
646 |
|
647 |
/** |
648 |
* Returns a list-iterator of the elements in this list (in proper |
649 |
* sequence), starting at the specified position in the list. |
650 |
* Obeys the general contract of <tt>List.listIterator(int)</tt>.<p> |
651 |
* |
652 |
* The list-iterator is <i>fail-fast</i>: if the list is structurally |
653 |
* modified at any time after the Iterator is created, in any way except |
654 |
* through the list-iterator's own <tt>remove</tt> or <tt>add</tt> |
655 |
* methods, the list-iterator will throw a |
656 |
* <tt>ConcurrentModificationException</tt>. Thus, in the face of |
657 |
* concurrent modification, the iterator fails quickly and cleanly, rather |
658 |
* than risking arbitrary, non-deterministic behavior at an undetermined |
659 |
* time in the future. |
660 |
* |
661 |
* @param index index of first element to be returned from the |
662 |
* list-iterator (by a call to <tt>next</tt>). |
663 |
* @return a ListIterator of the elements in this list (in proper |
664 |
* sequence), starting at the specified position in the list. |
665 |
* @throws IndexOutOfBoundsException if index is out of range |
666 |
* (<tt>index < 0 || index > size()</tt>). |
667 |
* @see List#listIterator(int) |
668 |
*/ |
669 |
public ListIterator<E> listIterator(int index) { |
670 |
return new ListItr(index); |
671 |
} |
672 |
|
673 |
private class ListItr implements ListIterator<E> { |
674 |
private Entry<E> lastReturned = header; |
675 |
private Entry<E> next; |
676 |
private int nextIndex; |
677 |
private int expectedModCount = modCount; |
678 |
|
679 |
ListItr(int index) { |
680 |
if (index < 0 || index > size) |
681 |
throw new IndexOutOfBoundsException("Index: "+index+ |
682 |
", Size: "+size); |
683 |
if (index < (size >> 1)) { |
684 |
next = header.next; |
685 |
for (nextIndex=0; nextIndex<index; nextIndex++) |
686 |
next = next.next; |
687 |
} else { |
688 |
next = header; |
689 |
for (nextIndex=size; nextIndex>index; nextIndex--) |
690 |
next = next.previous; |
691 |
} |
692 |
} |
693 |
|
694 |
public boolean hasNext() { |
695 |
return nextIndex != size; |
696 |
} |
697 |
|
698 |
public E next() { |
699 |
checkForComodification(); |
700 |
if (nextIndex == size) |
701 |
throw new NoSuchElementException(); |
702 |
|
703 |
lastReturned = next; |
704 |
next = next.next; |
705 |
nextIndex++; |
706 |
return lastReturned.element; |
707 |
} |
708 |
|
709 |
public boolean hasPrevious() { |
710 |
return nextIndex != 0; |
711 |
} |
712 |
|
713 |
public E previous() { |
714 |
if (nextIndex == 0) |
715 |
throw new NoSuchElementException(); |
716 |
|
717 |
lastReturned = next = next.previous; |
718 |
nextIndex--; |
719 |
checkForComodification(); |
720 |
return lastReturned.element; |
721 |
} |
722 |
|
723 |
public int nextIndex() { |
724 |
return nextIndex; |
725 |
} |
726 |
|
727 |
public int previousIndex() { |
728 |
return nextIndex-1; |
729 |
} |
730 |
|
731 |
public void remove() { |
732 |
checkForComodification(); |
733 |
Entry<E> lastNext = lastReturned.next; |
734 |
try { |
735 |
LinkedList.this.remove(lastReturned); |
736 |
} catch (NoSuchElementException e) { |
737 |
throw new IllegalStateException(); |
738 |
} |
739 |
if (next==lastReturned) |
740 |
next = lastNext; |
741 |
else |
742 |
nextIndex--; |
743 |
lastReturned = header; |
744 |
expectedModCount++; |
745 |
} |
746 |
|
747 |
public void set(E o) { |
748 |
if (lastReturned == header) |
749 |
throw new IllegalStateException(); |
750 |
checkForComodification(); |
751 |
lastReturned.element = o; |
752 |
} |
753 |
|
754 |
public void add(E o) { |
755 |
checkForComodification(); |
756 |
lastReturned = header; |
757 |
addBefore(o, next); |
758 |
nextIndex++; |
759 |
expectedModCount++; |
760 |
} |
761 |
|
762 |
final void checkForComodification() { |
763 |
if (modCount != expectedModCount) |
764 |
throw new ConcurrentModificationException(); |
765 |
} |
766 |
} |
767 |
|
768 |
private static class Entry<E> { |
769 |
E element; |
770 |
Entry<E> next; |
771 |
Entry<E> previous; |
772 |
|
773 |
Entry(E element, Entry<E> next, Entry<E> previous) { |
774 |
this.element = element; |
775 |
this.next = next; |
776 |
this.previous = previous; |
777 |
} |
778 |
} |
779 |
|
780 |
private Entry<E> addBefore(E o, Entry<E> e) { |
781 |
Entry<E> newEntry = new Entry<E>(o, e, e.previous); |
782 |
newEntry.previous.next = newEntry; |
783 |
newEntry.next.previous = newEntry; |
784 |
size++; |
785 |
modCount++; |
786 |
return newEntry; |
787 |
} |
788 |
|
789 |
private E remove(Entry<E> e) { |
790 |
if (e == header) |
791 |
throw new NoSuchElementException(); |
792 |
|
793 |
E result = e.element; |
794 |
e.previous.next = e.next; |
795 |
e.next.previous = e.previous; |
796 |
e.next = e.previous = null; |
797 |
e.element = null; |
798 |
size--; |
799 |
modCount++; |
800 |
return result; |
801 |
} |
802 |
|
803 |
/** |
804 |
* Returns a shallow copy of this <tt>LinkedList</tt>. (The elements |
805 |
* themselves are not cloned.) |
806 |
* |
807 |
* @return a shallow copy of this <tt>LinkedList</tt> instance. |
808 |
*/ |
809 |
public Object clone() { |
810 |
LinkedList<E> clone = null; |
811 |
try { |
812 |
clone = (LinkedList<E>) super.clone(); |
813 |
} catch (CloneNotSupportedException e) { |
814 |
throw new InternalError(); |
815 |
} |
816 |
|
817 |
// Put clone into "virgin" state |
818 |
clone.header = new Entry<E>(null, null, null); |
819 |
clone.header.next = clone.header.previous = clone.header; |
820 |
clone.size = 0; |
821 |
clone.modCount = 0; |
822 |
|
823 |
// Initialize clone with our elements |
824 |
for (Entry<E> e = header.next; e != header; e = e.next) |
825 |
clone.add(e.element); |
826 |
|
827 |
return clone; |
828 |
} |
829 |
|
830 |
/** |
831 |
* Returns an array containing all of the elements in this list |
832 |
* in the correct order. |
833 |
* |
834 |
* @return an array containing all of the elements in this list |
835 |
* in the correct order. |
836 |
*/ |
837 |
public Object[] toArray() { |
838 |
Object[] result = new Object[size]; |
839 |
int i = 0; |
840 |
for (Entry<E> e = header.next; e != header; e = e.next) |
841 |
result[i++] = e.element; |
842 |
return result; |
843 |
} |
844 |
|
845 |
/** |
846 |
* Returns an array containing all of the elements in this list in |
847 |
* the correct order; the runtime type of the returned array is that of |
848 |
* the specified array. If the list fits in the specified array, it |
849 |
* is returned therein. Otherwise, a new array is allocated with the |
850 |
* runtime type of the specified array and the size of this list.<p> |
851 |
* |
852 |
* If the list fits in the specified array with room to spare |
853 |
* (i.e., the array has more elements than the list), |
854 |
* the element in the array immediately following the end of the |
855 |
* collection is set to null. This is useful in determining the length |
856 |
* of the list <i>only</i> if the caller knows that the list |
857 |
* does not contain any null elements. |
858 |
* |
859 |
* @param a the array into which the elements of the list are to |
860 |
* be stored, if it is big enough; otherwise, a new array of the |
861 |
* same runtime type is allocated for this purpose. |
862 |
* @return an array containing the elements of the list. |
863 |
* @throws ArrayStoreException if the runtime type of a is not a |
864 |
* supertype of the runtime type of every element in this list. |
865 |
* @throws NullPointerException if the specified array is null. |
866 |
*/ |
867 |
public <T> T[] toArray(T[] a) { |
868 |
if (a.length < size) |
869 |
a = (T[])java.lang.reflect.Array.newInstance( |
870 |
a.getClass().getComponentType(), size); |
871 |
int i = 0; |
872 |
Object[] result = a; |
873 |
for (Entry<E> e = header.next; e != header; e = e.next) |
874 |
result[i++] = e.element; |
875 |
|
876 |
if (a.length > size) |
877 |
a[size] = null; |
878 |
|
879 |
return a; |
880 |
} |
881 |
|
882 |
private static final long serialVersionUID = 876323262645176354L; |
883 |
|
884 |
/** |
885 |
* Save the state of this <tt>LinkedList</tt> instance to a stream (that |
886 |
* is, serialize it). |
887 |
* |
888 |
* @serialData The size of the list (the number of elements it |
889 |
* contains) is emitted (int), followed by all of its |
890 |
* elements (each an Object) in the proper order. |
891 |
*/ |
892 |
private void writeObject(java.io.ObjectOutputStream s) |
893 |
throws java.io.IOException { |
894 |
// Write out any hidden serialization magic |
895 |
s.defaultWriteObject(); |
896 |
|
897 |
// Write out size |
898 |
s.writeInt(size); |
899 |
|
900 |
// Write out all elements in the proper order. |
901 |
for (Entry e = header.next; e != header; e = e.next) |
902 |
s.writeObject(e.element); |
903 |
} |
904 |
|
905 |
/** |
906 |
* Reconstitute this <tt>LinkedList</tt> instance from a stream (that is |
907 |
* deserialize it). |
908 |
*/ |
909 |
private void readObject(java.io.ObjectInputStream s) |
910 |
throws java.io.IOException, ClassNotFoundException { |
911 |
// Read in any hidden serialization magic |
912 |
s.defaultReadObject(); |
913 |
|
914 |
// Read in size |
915 |
int size = s.readInt(); |
916 |
|
917 |
// Initialize header |
918 |
header = new Entry<E>(null, null, null); |
919 |
header.next = header.previous = header; |
920 |
|
921 |
// Read in all elements in the proper order. |
922 |
for (int i=0; i<size; i++) |
923 |
addBefore((E)s.readObject(), header); |
924 |
} |
925 |
} |