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/* |
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* %W% %E% |
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* |
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* Copyright 2005 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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import java.util.*; // for javadoc (till 6280605 is fixed) |
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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, {@linkplain Queue queue}, or {@linkplain Deque |
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* double-ended queue}. <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.<p> |
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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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* <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 <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 |
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* any way except through the Iterator's own <tt>remove</tt> or |
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* <tt>add</tt> 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 <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> |
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* |
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* <p>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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* @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 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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addBefore(e, header.next); |
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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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addBefore(e, 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 |
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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 <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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* <p>This method is equivalent to {@link #addLast}. |
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* |
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* @param e element to be appended to this list |
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* @return <tt>true</tt> (as specified by {@link Collection#add}) |
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*/ |
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public boolean add(E e) { |
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addBefore(e, 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 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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* <tt>i</tt> 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 <tt>true</tt> 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 <tt>true</tt> 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 (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. (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 <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 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 <tt>true</tt> 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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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. |
310 |
* |
311 |
* @param index index of the element to return |
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* @return the element at the specified position in this list |
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* @throws IndexOutOfBoundsException {@inheritDoc} |
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*/ |
315 |
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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/** |
320 |
* Replaces the element at the specified position in this list with the |
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* specified element. |
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* |
323 |
* @param index index of the element to replace |
324 |
* @param element element to be stored at the specified position |
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* @return the element previously at the specified position |
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* @throws IndexOutOfBoundsException {@inheritDoc} |
327 |
*/ |
328 |
public E set(int index, E element) { |
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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. |
337 |
* Shifts the element currently at that position (if any) and any |
338 |
* subsequent elements to the right (adds one to their indices). |
339 |
* |
340 |
* @param index index at which the specified element is to be inserted |
341 |
* @param element element to be inserted |
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* @throws IndexOutOfBoundsException {@inheritDoc} |
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*/ |
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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 be removed |
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* @return the element previously at the specified position |
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* @throws IndexOutOfBoundsException {@inheritDoc} |
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*/ |
357 |
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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* Returns 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 |
381 |
|
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/** |
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* Returns the index of the first occurrence of the specified element |
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* in this list, or -1 if this list does not contain the element. |
385 |
* More formally, returns the lowest index <tt>i</tt> such that |
386 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, |
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* or -1 if there is no such index. |
388 |
* |
389 |
* @param o element to search for |
390 |
* @return the index of the first occurrence of the specified element in |
391 |
* this list, or -1 if this list does not contain the element |
392 |
*/ |
393 |
public int indexOf(Object o) { |
394 |
int index = 0; |
395 |
if (o==null) { |
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for (Entry e = header.next; e != header; e = e.next) { |
397 |
if (e.element==null) |
398 |
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 of the last occurrence of the specified element |
413 |
* in this list, or -1 if this list does not contain the element. |
414 |
* More formally, returns the highest index <tt>i</tt> such that |
415 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, |
416 |
* or -1 if there is no such index. |
417 |
* |
418 |
* @param o element to search for |
419 |
* @return the index of the last occurrence of the specified element in |
420 |
* this list, or -1 if this list does not contain the element |
421 |
*/ |
422 |
public int lastIndexOf(Object o) { |
423 |
int index = size; |
424 |
if (o==null) { |
425 |
for (Entry e = header.previous; e != header; e = e.previous) { |
426 |
index--; |
427 |
if (e.element==null) |
428 |
return index; |
429 |
} |
430 |
} else { |
431 |
for (Entry e = header.previous; e != header; e = e.previous) { |
432 |
index--; |
433 |
if (o.equals(e.element)) |
434 |
return index; |
435 |
} |
436 |
} |
437 |
return -1; |
438 |
} |
439 |
|
440 |
// Queue operations. |
441 |
|
442 |
/** |
443 |
* Retrieves, but does not remove, the head (first element) of this list. |
444 |
* @return the head of this list, or <tt>null</tt> if this list is empty |
445 |
* @since 1.5 |
446 |
*/ |
447 |
public E peek() { |
448 |
if (size==0) |
449 |
return null; |
450 |
return getFirst(); |
451 |
} |
452 |
|
453 |
/** |
454 |
* Retrieves, but does not remove, the head (first element) of this list. |
455 |
* @return the head of this list |
456 |
* @throws NoSuchElementException if this list is empty |
457 |
* @since 1.5 |
458 |
*/ |
459 |
public E element() { |
460 |
return getFirst(); |
461 |
} |
462 |
|
463 |
/** |
464 |
* Retrieves and removes the head (first element) of this list |
465 |
* @return the head of this list, or <tt>null</tt> if this list is empty |
466 |
* @since 1.5 |
467 |
*/ |
468 |
public E poll() { |
469 |
if (size==0) |
470 |
return null; |
471 |
return removeFirst(); |
472 |
} |
473 |
|
474 |
/** |
475 |
* Retrieves and removes the head (first element) of this list. |
476 |
* |
477 |
* @return the head of this list |
478 |
* @throws NoSuchElementException if this list 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 e the element to add |
489 |
* @return <tt>true</tt> (as specified by {@link Queue#offer}) |
490 |
* @since 1.5 |
491 |
*/ |
492 |
public boolean offer(E e) { |
493 |
return add(e); |
494 |
} |
495 |
|
496 |
// Deque operations |
497 |
/** |
498 |
* Inserts the specified element at the front of this list. |
499 |
* |
500 |
* @param e the element to insert |
501 |
* @return <tt>true</tt> (as specified by {@link Deque#offerFirst}) |
502 |
* @since 1.6 |
503 |
*/ |
504 |
public boolean offerFirst(E e) { |
505 |
addFirst(e); |
506 |
return true; |
507 |
} |
508 |
|
509 |
/** |
510 |
* Inserts the specified element at the end of this list. |
511 |
* |
512 |
* @param e the element to insert |
513 |
* @return <tt>true</tt> (as specified by {@link Deque#offerLast}) |
514 |
* @since 1.6 |
515 |
*/ |
516 |
public boolean offerLast(E e) { |
517 |
addLast(e); |
518 |
return true; |
519 |
} |
520 |
|
521 |
/** |
522 |
* Retrieves, but does not remove, the first element of this list, |
523 |
* or returns <tt>null</tt> if this list is empty. |
524 |
* |
525 |
* @return the first element of this list, or <tt>null</tt> |
526 |
* if this list is empty |
527 |
* @since 1.6 |
528 |
*/ |
529 |
public E peekFirst() { |
530 |
if (size==0) |
531 |
return null; |
532 |
return getFirst(); |
533 |
} |
534 |
|
535 |
/** |
536 |
* Retrieves, but does not remove, the last element of this list, |
537 |
* or returns <tt>null</tt> if this list is empty. |
538 |
* |
539 |
* @return the last element of this list, or <tt>null</tt> |
540 |
* if this list is empty |
541 |
* @since 1.6 |
542 |
*/ |
543 |
public E peekLast() { |
544 |
if (size==0) |
545 |
return null; |
546 |
return getLast(); |
547 |
} |
548 |
|
549 |
/** |
550 |
* Retrieves and removes the first element of this list, |
551 |
* or returns <tt>null</tt> if this list is empty. |
552 |
* |
553 |
* @return the first element of this list, or <tt>null</tt> if |
554 |
* this list is empty |
555 |
* @since 1.6 |
556 |
*/ |
557 |
public E pollFirst() { |
558 |
if (size==0) |
559 |
return null; |
560 |
return removeFirst(); |
561 |
} |
562 |
|
563 |
/** |
564 |
* Retrieves and removes the last element of this list, |
565 |
* or returns <tt>null</tt> if this list is empty. |
566 |
* |
567 |
* @return the last element of this list, or <tt>null</tt> if |
568 |
* this list is empty |
569 |
* @since 1.6 |
570 |
*/ |
571 |
public E pollLast() { |
572 |
if (size==0) |
573 |
return null; |
574 |
return removeLast(); |
575 |
} |
576 |
|
577 |
/** |
578 |
* Pushes an element onto the stack represented by this list. In other |
579 |
* words, inserts the element at the front of this list. |
580 |
* |
581 |
* <p>This method is equivalent to {@link #addFirst}. |
582 |
* |
583 |
* @param e the element to push |
584 |
* @since 1.6 |
585 |
*/ |
586 |
public void push(E e) { |
587 |
addFirst(e); |
588 |
} |
589 |
|
590 |
/** |
591 |
* Pops an element from the stack represented by this list. In other |
592 |
* words, removes and returns the first element of this list. |
593 |
* |
594 |
* <p>This method is equivalent to {@link #removeFirst()}. |
595 |
* |
596 |
* @return the element at the front of this list (which is the top |
597 |
* of the stack represented by this list) |
598 |
* @throws NoSuchElementException if this list is empty |
599 |
* @since 1.6 |
600 |
*/ |
601 |
public E pop() { |
602 |
return removeFirst(); |
603 |
} |
604 |
|
605 |
/** |
606 |
* Removes the first occurrence of the specified element in this |
607 |
* list (when traversing the list from head to tail). If the list |
608 |
* does not contain the element, it is unchanged. |
609 |
* |
610 |
* @param o element to be removed from this list, if present |
611 |
* @return <tt>true</tt> if the list contained the specified element |
612 |
* @since 1.6 |
613 |
*/ |
614 |
public boolean removeFirstOccurrence(Object o) { |
615 |
return remove(o); |
616 |
} |
617 |
|
618 |
/** |
619 |
* Removes the last occurrence of the specified element in this |
620 |
* list (when traversing the list from head to tail). If the list |
621 |
* does not contain the element, it is unchanged. |
622 |
* |
623 |
* @param o element to be removed from this list, if present |
624 |
* @return <tt>true</tt> if the list contained the specified element |
625 |
* @since 1.6 |
626 |
*/ |
627 |
public boolean removeLastOccurrence(Object o) { |
628 |
if (o==null) { |
629 |
for (Entry<E> e = header.previous; e != header; e = e.previous) { |
630 |
if (e.element==null) { |
631 |
remove(e); |
632 |
return true; |
633 |
} |
634 |
} |
635 |
} else { |
636 |
for (Entry<E> e = header.previous; e != header; e = e.previous) { |
637 |
if (o.equals(e.element)) { |
638 |
remove(e); |
639 |
return true; |
640 |
} |
641 |
} |
642 |
} |
643 |
return false; |
644 |
} |
645 |
|
646 |
/** |
647 |
* Returns a list-iterator of the elements in this list (in proper |
648 |
* sequence), starting at the specified position in the list. |
649 |
* Obeys the general contract of <tt>List.listIterator(int)</tt>.<p> |
650 |
* |
651 |
* The list-iterator is <i>fail-fast</i>: if the list is structurally |
652 |
* modified at any time after the Iterator is created, in any way except |
653 |
* through the list-iterator's own <tt>remove</tt> or <tt>add</tt> |
654 |
* methods, the list-iterator will throw a |
655 |
* <tt>ConcurrentModificationException</tt>. Thus, in the face of |
656 |
* concurrent modification, the iterator fails quickly and cleanly, rather |
657 |
* than risking arbitrary, non-deterministic behavior at an undetermined |
658 |
* time in the future. |
659 |
* |
660 |
* @param index index of the first element to be returned from the |
661 |
* list-iterator (by a call to <tt>next</tt>) |
662 |
* @return a ListIterator of the elements in this list (in proper |
663 |
* sequence), starting at the specified position in the list |
664 |
* @throws IndexOutOfBoundsException {@inheritDoc} |
665 |
* @see List#listIterator(int) |
666 |
*/ |
667 |
public ListIterator<E> listIterator(int index) { |
668 |
return new ListItr(index); |
669 |
} |
670 |
|
671 |
private class ListItr implements ListIterator<E> { |
672 |
private Entry<E> lastReturned = header; |
673 |
private Entry<E> next; |
674 |
private int nextIndex; |
675 |
private int expectedModCount = modCount; |
676 |
|
677 |
ListItr(int index) { |
678 |
if (index < 0 || index > size) |
679 |
throw new IndexOutOfBoundsException("Index: "+index+ |
680 |
", Size: "+size); |
681 |
if (index < (size >> 1)) { |
682 |
next = header.next; |
683 |
for (nextIndex=0; nextIndex<index; nextIndex++) |
684 |
next = next.next; |
685 |
} else { |
686 |
next = header; |
687 |
for (nextIndex=size; nextIndex>index; nextIndex--) |
688 |
next = next.previous; |
689 |
} |
690 |
} |
691 |
|
692 |
public boolean hasNext() { |
693 |
return nextIndex != size; |
694 |
} |
695 |
|
696 |
public E next() { |
697 |
checkForComodification(); |
698 |
if (nextIndex == size) |
699 |
throw new NoSuchElementException(); |
700 |
|
701 |
lastReturned = next; |
702 |
next = next.next; |
703 |
nextIndex++; |
704 |
return lastReturned.element; |
705 |
} |
706 |
|
707 |
public boolean hasPrevious() { |
708 |
return nextIndex != 0; |
709 |
} |
710 |
|
711 |
public E previous() { |
712 |
if (nextIndex == 0) |
713 |
throw new NoSuchElementException(); |
714 |
|
715 |
lastReturned = next = next.previous; |
716 |
nextIndex--; |
717 |
checkForComodification(); |
718 |
return lastReturned.element; |
719 |
} |
720 |
|
721 |
public int nextIndex() { |
722 |
return nextIndex; |
723 |
} |
724 |
|
725 |
public int previousIndex() { |
726 |
return nextIndex-1; |
727 |
} |
728 |
|
729 |
public void remove() { |
730 |
checkForComodification(); |
731 |
Entry<E> lastNext = lastReturned.next; |
732 |
try { |
733 |
LinkedList.this.remove(lastReturned); |
734 |
} catch (NoSuchElementException e) { |
735 |
throw new IllegalStateException(); |
736 |
} |
737 |
if (next==lastReturned) |
738 |
next = lastNext; |
739 |
else |
740 |
nextIndex--; |
741 |
lastReturned = header; |
742 |
expectedModCount++; |
743 |
} |
744 |
|
745 |
public void set(E e) { |
746 |
if (lastReturned == header) |
747 |
throw new IllegalStateException(); |
748 |
checkForComodification(); |
749 |
lastReturned.element = e; |
750 |
} |
751 |
|
752 |
public void add(E e) { |
753 |
checkForComodification(); |
754 |
lastReturned = header; |
755 |
addBefore(e, next); |
756 |
nextIndex++; |
757 |
expectedModCount++; |
758 |
} |
759 |
|
760 |
final void checkForComodification() { |
761 |
if (modCount != expectedModCount) |
762 |
throw new ConcurrentModificationException(); |
763 |
} |
764 |
} |
765 |
|
766 |
private static class Entry<E> { |
767 |
E element; |
768 |
Entry<E> next; |
769 |
Entry<E> previous; |
770 |
|
771 |
Entry(E element, Entry<E> next, Entry<E> previous) { |
772 |
this.element = element; |
773 |
this.next = next; |
774 |
this.previous = previous; |
775 |
} |
776 |
} |
777 |
|
778 |
private Entry<E> addBefore(E e, Entry<E> entry) { |
779 |
Entry<E> newEntry = new Entry<E>(e, entry, entry.previous); |
780 |
newEntry.previous.next = newEntry; |
781 |
newEntry.next.previous = newEntry; |
782 |
size++; |
783 |
modCount++; |
784 |
return newEntry; |
785 |
} |
786 |
|
787 |
private E remove(Entry<E> e) { |
788 |
if (e == header) |
789 |
throw new NoSuchElementException(); |
790 |
|
791 |
E result = e.element; |
792 |
e.previous.next = e.next; |
793 |
e.next.previous = e.previous; |
794 |
e.next = e.previous = null; |
795 |
e.element = null; |
796 |
size--; |
797 |
modCount++; |
798 |
return result; |
799 |
} |
800 |
|
801 |
public Iterator<E> descendingIterator() { |
802 |
return new DescendingIterator(); |
803 |
} |
804 |
|
805 |
/** Adapter to provide descending iterators via ListItr.previous */ |
806 |
private class DescendingIterator implements Iterator { |
807 |
final ListItr itr = new ListItr(size()); |
808 |
public boolean hasNext() { |
809 |
return itr.hasPrevious(); |
810 |
} |
811 |
public E next() { |
812 |
return itr.previous(); |
813 |
} |
814 |
public void remove() { |
815 |
itr.remove(); |
816 |
} |
817 |
} |
818 |
|
819 |
/** |
820 |
* Returns a shallow copy of this <tt>LinkedList</tt>. (The elements |
821 |
* themselves are not cloned.) |
822 |
* |
823 |
* @return a shallow copy of this <tt>LinkedList</tt> instance |
824 |
*/ |
825 |
public Object clone() { |
826 |
LinkedList<E> clone = null; |
827 |
try { |
828 |
clone = (LinkedList<E>) super.clone(); |
829 |
} catch (CloneNotSupportedException e) { |
830 |
throw new InternalError(); |
831 |
} |
832 |
|
833 |
// Put clone into "virgin" state |
834 |
clone.header = new Entry<E>(null, null, null); |
835 |
clone.header.next = clone.header.previous = clone.header; |
836 |
clone.size = 0; |
837 |
clone.modCount = 0; |
838 |
|
839 |
// Initialize clone with our elements |
840 |
for (Entry<E> e = header.next; e != header; e = e.next) |
841 |
clone.add(e.element); |
842 |
|
843 |
return clone; |
844 |
} |
845 |
|
846 |
/** |
847 |
* Returns an array containing all of the elements in this list |
848 |
* in proper sequence (from first to last element). |
849 |
* |
850 |
* <p>The returned array will be "safe" in that no references to it are |
851 |
* maintained by this list. (In other words, this method must allocate |
852 |
* a new array). The caller is thus free to modify the returned array. |
853 |
* |
854 |
* <p>This method acts as bridge between array-based and collection-based |
855 |
* APIs. |
856 |
* |
857 |
* @return an array containing all of the elements in this list |
858 |
* in proper sequence |
859 |
*/ |
860 |
public Object[] toArray() { |
861 |
Object[] result = new Object[size]; |
862 |
int i = 0; |
863 |
for (Entry<E> e = header.next; e != header; e = e.next) |
864 |
result[i++] = e.element; |
865 |
return result; |
866 |
} |
867 |
|
868 |
/** |
869 |
* Returns an array containing all of the elements in this list in |
870 |
* proper sequence (from first to last element); the runtime type of |
871 |
* the returned array is that of the specified array. If the list fits |
872 |
* in the specified array, it is returned therein. Otherwise, a new |
873 |
* array is allocated with the runtime type of the specified array and |
874 |
* the size of this list. |
875 |
* |
876 |
* <p>If the list fits in the specified array with room to spare (i.e., |
877 |
* the array has more elements than the list), the element in the array |
878 |
* immediately following the end of the list is set to <tt>null</tt>. |
879 |
* (This is useful in determining the length of the list <i>only</i> if |
880 |
* the caller knows that the list does not contain any null elements.) |
881 |
* |
882 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
883 |
* array-based and collection-based APIs. Further, this method allows |
884 |
* precise control over the runtime type of the output array, and may, |
885 |
* under certain circumstances, be used to save allocation costs. |
886 |
* |
887 |
* <p>Suppose <tt>x</tt> is a list known to contain only strings. |
888 |
* The following code can be used to dump the list into a newly |
889 |
* allocated array of <tt>String</tt>: |
890 |
* |
891 |
* <pre> |
892 |
* String[] y = x.toArray(new String[0]);</pre> |
893 |
* |
894 |
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
895 |
* <tt>toArray()</tt>. |
896 |
* |
897 |
* @param a the array into which the elements of the list are to |
898 |
* be stored, if it is big enough; otherwise, a new array of the |
899 |
* same runtime type is allocated for this purpose. |
900 |
* @return an array containing the elements of the list |
901 |
* @throws ArrayStoreException if the runtime type of the specified array |
902 |
* is not a supertype of the runtime type of every element in |
903 |
* this list |
904 |
* @throws NullPointerException if the specified array is null |
905 |
*/ |
906 |
public <T> T[] toArray(T[] a) { |
907 |
if (a.length < size) |
908 |
a = (T[])java.lang.reflect.Array.newInstance( |
909 |
a.getClass().getComponentType(), size); |
910 |
int i = 0; |
911 |
Object[] result = a; |
912 |
for (Entry<E> e = header.next; e != header; e = e.next) |
913 |
result[i++] = e.element; |
914 |
|
915 |
if (a.length > size) |
916 |
a[size] = null; |
917 |
|
918 |
return a; |
919 |
} |
920 |
|
921 |
private static final long serialVersionUID = 876323262645176354L; |
922 |
|
923 |
/** |
924 |
* Save the state of this <tt>LinkedList</tt> instance to a stream (that |
925 |
* is, serialize it). |
926 |
* |
927 |
* @serialData The size of the list (the number of elements it |
928 |
* contains) is emitted (int), followed by all of its |
929 |
* elements (each an Object) in the proper order. |
930 |
*/ |
931 |
private void writeObject(java.io.ObjectOutputStream s) |
932 |
throws java.io.IOException { |
933 |
// Write out any hidden serialization magic |
934 |
s.defaultWriteObject(); |
935 |
|
936 |
// Write out size |
937 |
s.writeInt(size); |
938 |
|
939 |
// Write out all elements in the proper order. |
940 |
for (Entry e = header.next; e != header; e = e.next) |
941 |
s.writeObject(e.element); |
942 |
} |
943 |
|
944 |
/** |
945 |
* Reconstitute this <tt>LinkedList</tt> instance from a stream (that is |
946 |
* deserialize it). |
947 |
*/ |
948 |
private void readObject(java.io.ObjectInputStream s) |
949 |
throws java.io.IOException, ClassNotFoundException { |
950 |
// Read in any hidden serialization magic |
951 |
s.defaultReadObject(); |
952 |
|
953 |
// Read in size |
954 |
int size = s.readInt(); |
955 |
|
956 |
// Initialize header |
957 |
header = new Entry<E>(null, null, null); |
958 |
header.next = header.previous = header; |
959 |
|
960 |
// Read in all elements in the proper order. |
961 |
for (int i=0; i<size; i++) |
962 |
addBefore((E)s.readObject(), header); |
963 |
} |
964 |
} |