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/* |
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* @(#)LinkedList.java 1.43 01/12/03 |
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* |
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* Copyright 2002 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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* <b>JSR166: Added Queue operations</b>.<p> |
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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 (deque).<p> |
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* |
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* All of the stack/queue/deque operations could be easily recast in terms of |
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* the standard list operations. They're included here primarily for |
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* convenience, though they may run slightly faster than the equivalent List |
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* 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 begining 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> |
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* |
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* @author Josh Bloch |
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* @version 1.43, 12/03/01 |
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* @see java.util.List |
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* @see java.util.ArrayList |
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* @see java.util.Vector |
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* @see java.util.Collections#synchronizedList(java.util.List) |
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* @since 1.2 |
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*/ |
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|
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public class LinkedList extends AbstractSequentialList |
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implements List, Queue, Cloneable, java.io.Serializable |
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{ |
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private transient Entry header = new Entry(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 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 Object 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 Object 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 Object removeFirst() { |
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Object first = header.next.element; |
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remove(header.next); |
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return first; |
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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 Object removeLast() { |
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Object last = header.previous.element; |
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remove(header.previous); |
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return last; |
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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(Object 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(Object 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(Object 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 = 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 = 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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*/ |
238 |
public boolean addAll(Collection 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 |
247 |
* in the list in the order that they are returned by the |
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* specified collection's iterator. |
249 |
* |
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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. |
254 |
* @throws IndexOutOfBoundsException if the specified index is out of |
255 |
* range (<tt>index < 0 || index > size()</tt>). |
256 |
* @throws NullPointerException if the specified collection is null. |
257 |
*/ |
258 |
public boolean addAll(int index, Collection c) { |
259 |
int numNew = c.size(); |
260 |
if (numNew==0) |
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return false; |
262 |
modCount++; |
263 |
|
264 |
Entry successor = (index==size ? header : entry(index)); |
265 |
Entry predecessor = successor.previous; |
266 |
Iterator it = c.iterator(); |
267 |
for (int i=0; i<numNew; i++) { |
268 |
Entry e = new Entry(it.next(), 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; |
273 |
|
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size += numNew; |
275 |
return true; |
276 |
} |
277 |
|
278 |
/** |
279 |
* Removes all of the elements from this list. |
280 |
*/ |
281 |
public void clear() { |
282 |
modCount++; |
283 |
header.next = header.previous = header; |
284 |
size = 0; |
285 |
} |
286 |
|
287 |
|
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// Positional Access Operations |
289 |
|
290 |
/** |
291 |
* Returns the element at the specified position in this list. |
292 |
* |
293 |
* @param index index of element to return. |
294 |
* @return the element at the specified position in this list. |
295 |
* |
296 |
* @throws IndexOutOfBoundsException if the specified index is is out of |
297 |
* range (<tt>index < 0 || index >= size()</tt>). |
298 |
*/ |
299 |
public Object get(int index) { |
300 |
return entry(index).element; |
301 |
} |
302 |
|
303 |
/** |
304 |
* Replaces the element at the specified position in this list with the |
305 |
* specified element. |
306 |
* |
307 |
* @param index index of element to replace. |
308 |
* @param element element to be stored at the specified position. |
309 |
* @return the element previously at the specified position. |
310 |
* @throws IndexOutOfBoundsException if the specified index is out of |
311 |
* range (<tt>index < 0 || index >= size()</tt>). |
312 |
*/ |
313 |
public Object set(int index, Object element) { |
314 |
Entry e = entry(index); |
315 |
Object oldVal = e.element; |
316 |
e.element = element; |
317 |
return oldVal; |
318 |
} |
319 |
|
320 |
/** |
321 |
* Inserts the specified element at the specified position in this list. |
322 |
* Shifts the element currently at that position (if any) and any |
323 |
* subsequent elements to the right (adds one to their indices). |
324 |
* |
325 |
* @param index index at which the specified element is to be inserted. |
326 |
* @param element element to be inserted. |
327 |
* |
328 |
* @throws IndexOutOfBoundsException if the specified index is out of |
329 |
* range (<tt>index < 0 || index > size()</tt>). |
330 |
*/ |
331 |
public void add(int index, Object element) { |
332 |
addBefore(element, (index==size ? header : entry(index))); |
333 |
} |
334 |
|
335 |
/** |
336 |
* Removes the element at the specified position in this list. Shifts any |
337 |
* subsequent elements to the left (subtracts one from their indices). |
338 |
* Returns the element that was removed from the list. |
339 |
* |
340 |
* @param index the index of the element to removed. |
341 |
* @return the element previously at the specified position. |
342 |
* |
343 |
* @throws IndexOutOfBoundsException if the specified index is out of |
344 |
* range (<tt>index < 0 || index >= size()</tt>). |
345 |
*/ |
346 |
public Object remove(int index) { |
347 |
Entry e = entry(index); |
348 |
remove(e); |
349 |
return e.element; |
350 |
} |
351 |
|
352 |
/** |
353 |
* Return the indexed entry. |
354 |
*/ |
355 |
private Entry entry(int index) { |
356 |
if (index < 0 || index >= size) |
357 |
throw new IndexOutOfBoundsException("Index: "+index+ |
358 |
", Size: "+size); |
359 |
Entry e = header; |
360 |
if (index < (size >> 1)) { |
361 |
for (int i = 0; i <= index; i++) |
362 |
e = e.next; |
363 |
} else { |
364 |
for (int i = size; i > index; i--) |
365 |
e = e.previous; |
366 |
} |
367 |
return e; |
368 |
} |
369 |
|
370 |
|
371 |
// Search Operations |
372 |
|
373 |
/** |
374 |
* Returns the index in this list of the first occurrence of the |
375 |
* specified element, or -1 if the List does not contain this |
376 |
* element. More formally, returns the lowest index i such that |
377 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, or -1 if |
378 |
* there is no such index. |
379 |
* |
380 |
* @param o element to search for. |
381 |
* @return the index in this list of the first occurrence of the |
382 |
* specified element, or -1 if the list does not contain this |
383 |
* element. |
384 |
*/ |
385 |
public int indexOf(Object o) { |
386 |
int index = 0; |
387 |
if (o==null) { |
388 |
for (Entry e = header.next; e != header; e = e.next) { |
389 |
if (e.element==null) |
390 |
return index; |
391 |
index++; |
392 |
} |
393 |
} else { |
394 |
for (Entry e = header.next; e != header; e = e.next) { |
395 |
if (o.equals(e.element)) |
396 |
return index; |
397 |
index++; |
398 |
} |
399 |
} |
400 |
return -1; |
401 |
} |
402 |
|
403 |
/** |
404 |
* Returns the index in this list of the last occurrence of the |
405 |
* specified element, or -1 if the list does not contain this |
406 |
* element. More formally, returns the highest index i such that |
407 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, or -1 if |
408 |
* there is no such index. |
409 |
* |
410 |
* @param o element to search for. |
411 |
* @return the index in this list of the last occurrence of the |
412 |
* specified element, or -1 if the list does not contain this |
413 |
* element. |
414 |
*/ |
415 |
public int lastIndexOf(Object o) { |
416 |
int index = size; |
417 |
if (o==null) { |
418 |
for (Entry e = header.previous; e != header; e = e.previous) { |
419 |
index--; |
420 |
if (e.element==null) |
421 |
return index; |
422 |
} |
423 |
} else { |
424 |
for (Entry e = header.previous; e != header; e = e.previous) { |
425 |
index--; |
426 |
if (o.equals(e.element)) |
427 |
return index; |
428 |
} |
429 |
} |
430 |
return -1; |
431 |
} |
432 |
|
433 |
/** |
434 |
* Returns a list-iterator of the elements in this list (in proper |
435 |
* sequence), starting at the specified position in the list. |
436 |
* Obeys the general contract of <tt>List.listIterator(int)</tt>.<p> |
437 |
* |
438 |
* The list-iterator is <i>fail-fast</i>: if the list is structurally |
439 |
* modified at any time after the Iterator is created, in any way except |
440 |
* through the list-iterator's own <tt>remove</tt> or <tt>add</tt> |
441 |
* methods, the list-iterator will throw a |
442 |
* <tt>ConcurrentModificationException</tt>. Thus, in the face of |
443 |
* concurrent modification, the iterator fails quickly and cleanly, rather |
444 |
* than risking arbitrary, non-deterministic behavior at an undetermined |
445 |
* time in the future. |
446 |
* |
447 |
* @param index index of first element to be returned from the |
448 |
* list-iterator (by a call to <tt>next</tt>). |
449 |
* @return a ListIterator of the elements in this list (in proper |
450 |
* sequence), starting at the specified position in the list. |
451 |
* @throws IndexOutOfBoundsException if index is out of range |
452 |
* (<tt>index < 0 || index > size()</tt>). |
453 |
* @see java.util.List#listIterator(int) |
454 |
*/ |
455 |
public ListIterator listIterator(int index) { |
456 |
return new ListItr(index); |
457 |
} |
458 |
|
459 |
private class ListItr implements ListIterator { |
460 |
private Entry lastReturned = header; |
461 |
private Entry next; |
462 |
private int nextIndex; |
463 |
private int expectedModCount = modCount; |
464 |
|
465 |
ListItr(int index) { |
466 |
if (index < 0 || index > size) |
467 |
throw new IndexOutOfBoundsException("Index: "+index+ |
468 |
", Size: "+size); |
469 |
if (index < (size >> 1)) { |
470 |
next = header.next; |
471 |
for (nextIndex=0; nextIndex<index; nextIndex++) |
472 |
next = next.next; |
473 |
} else { |
474 |
next = header; |
475 |
for (nextIndex=size; nextIndex>index; nextIndex--) |
476 |
next = next.previous; |
477 |
} |
478 |
} |
479 |
|
480 |
public boolean hasNext() { |
481 |
return nextIndex != size; |
482 |
} |
483 |
|
484 |
public Object next() { |
485 |
checkForComodification(); |
486 |
if (nextIndex == size) |
487 |
throw new NoSuchElementException(); |
488 |
|
489 |
lastReturned = next; |
490 |
next = next.next; |
491 |
nextIndex++; |
492 |
return lastReturned.element; |
493 |
} |
494 |
|
495 |
public boolean hasPrevious() { |
496 |
return nextIndex != 0; |
497 |
} |
498 |
|
499 |
public Object previous() { |
500 |
if (nextIndex == 0) |
501 |
throw new NoSuchElementException(); |
502 |
|
503 |
lastReturned = next = next.previous; |
504 |
nextIndex--; |
505 |
checkForComodification(); |
506 |
return lastReturned.element; |
507 |
} |
508 |
|
509 |
public int nextIndex() { |
510 |
return nextIndex; |
511 |
} |
512 |
|
513 |
public int previousIndex() { |
514 |
return nextIndex-1; |
515 |
} |
516 |
|
517 |
public void remove() { |
518 |
checkForComodification(); |
519 |
try { |
520 |
LinkedList.this.remove(lastReturned); |
521 |
} catch (NoSuchElementException e) { |
522 |
throw new IllegalStateException(); |
523 |
} |
524 |
if (next==lastReturned) |
525 |
next = lastReturned.next; |
526 |
else |
527 |
nextIndex--; |
528 |
lastReturned = header; |
529 |
expectedModCount++; |
530 |
} |
531 |
|
532 |
public void set(Object o) { |
533 |
if (lastReturned == header) |
534 |
throw new IllegalStateException(); |
535 |
checkForComodification(); |
536 |
lastReturned.element = o; |
537 |
} |
538 |
|
539 |
public void add(Object o) { |
540 |
checkForComodification(); |
541 |
lastReturned = header; |
542 |
addBefore(o, next); |
543 |
nextIndex++; |
544 |
expectedModCount++; |
545 |
} |
546 |
|
547 |
final void checkForComodification() { |
548 |
if (modCount != expectedModCount) |
549 |
throw new ConcurrentModificationException(); |
550 |
} |
551 |
} |
552 |
|
553 |
private static class Entry { |
554 |
Object element; |
555 |
Entry next; |
556 |
Entry previous; |
557 |
|
558 |
Entry(Object element, Entry next, Entry previous) { |
559 |
this.element = element; |
560 |
this.next = next; |
561 |
this.previous = previous; |
562 |
} |
563 |
} |
564 |
|
565 |
private Entry addBefore(Object o, Entry e) { |
566 |
Entry newEntry = new Entry(o, e, e.previous); |
567 |
newEntry.previous.next = newEntry; |
568 |
newEntry.next.previous = newEntry; |
569 |
size++; |
570 |
modCount++; |
571 |
return newEntry; |
572 |
} |
573 |
|
574 |
private void remove(Entry e) { |
575 |
if (e == header) |
576 |
throw new NoSuchElementException(); |
577 |
|
578 |
e.previous.next = e.next; |
579 |
e.next.previous = e.previous; |
580 |
size--; |
581 |
modCount++; |
582 |
} |
583 |
|
584 |
/** |
585 |
* Returns a shallow copy of this <tt>LinkedList</tt>. (The elements |
586 |
* themselves are not cloned.) |
587 |
* |
588 |
* @return a shallow copy of this <tt>LinkedList</tt> instance. |
589 |
*/ |
590 |
public Object clone() { |
591 |
LinkedList clone = null; |
592 |
try { |
593 |
clone = (LinkedList)super.clone(); |
594 |
} catch (CloneNotSupportedException e) { |
595 |
throw new InternalError(); |
596 |
} |
597 |
|
598 |
// Put clone into "virgin" state |
599 |
clone.header = new Entry(null, null, null); |
600 |
clone.header.next = clone.header.previous = clone.header; |
601 |
clone.size = 0; |
602 |
clone.modCount = 0; |
603 |
|
604 |
// Initialize clone with our elements |
605 |
for (Entry e = header.next; e != header; e = e.next) |
606 |
clone.add(e.element); |
607 |
|
608 |
return clone; |
609 |
} |
610 |
|
611 |
/** |
612 |
* Returns an array containing all of the elements in this list |
613 |
* in the correct order. |
614 |
* |
615 |
* @return an array containing all of the elements in this list |
616 |
* in the correct order. |
617 |
*/ |
618 |
public Object[] toArray() { |
619 |
Object[] result = new Object[size]; |
620 |
int i = 0; |
621 |
for (Entry e = header.next; e != header; e = e.next) |
622 |
result[i++] = e.element; |
623 |
return result; |
624 |
} |
625 |
|
626 |
/** |
627 |
* Returns an array containing all of the elements in this list in |
628 |
* the correct order; the runtime type of the returned array is that of |
629 |
* the specified array. If the list fits in the specified array, it |
630 |
* is returned therein. Otherwise, a new array is allocated with the |
631 |
* runtime type of the specified array and the size of this list.<p> |
632 |
* |
633 |
* If the list fits in the specified array with room to spare |
634 |
* (i.e., the array has more elements than the list), |
635 |
* the element in the array immediately following the end of the |
636 |
* collection is set to null. This is useful in determining the length |
637 |
* of the list <i>only</i> if the caller knows that the list |
638 |
* does not contain any null elements. |
639 |
* |
640 |
* @param a the array into which the elements of the list are to |
641 |
* be stored, if it is big enough; otherwise, a new array of the |
642 |
* same runtime type is allocated for this purpose. |
643 |
* @return an array containing the elements of the list. |
644 |
* @throws ArrayStoreException if the runtime type of a is not a |
645 |
* supertype of the runtime type of every element in this list. |
646 |
* @throws NullPointerException if the specified array is null. |
647 |
*/ |
648 |
public Object[] toArray(Object a[]) { |
649 |
if (a.length < size) |
650 |
a = (Object[])java.lang.reflect.Array.newInstance( |
651 |
a.getClass().getComponentType(), size); |
652 |
int i = 0; |
653 |
for (Entry e = header.next; e != header; e = e.next) |
654 |
a[i++] = e.element; |
655 |
|
656 |
if (a.length > size) |
657 |
a[size] = null; |
658 |
|
659 |
return a; |
660 |
} |
661 |
|
662 |
private static final long serialVersionUID = 876323262645176354L; |
663 |
|
664 |
/** |
665 |
* Save the state of this <tt>LinkedList</tt> instance to a stream (that |
666 |
* is, serialize it). |
667 |
* |
668 |
* @serialData The size of the list (the number of elements it |
669 |
* contains) is emitted (int), followed by all of its |
670 |
* elements (each an Object) in the proper order. |
671 |
*/ |
672 |
private synchronized void writeObject(java.io.ObjectOutputStream s) |
673 |
throws java.io.IOException { |
674 |
// Write out any hidden serialization magic |
675 |
s.defaultWriteObject(); |
676 |
|
677 |
// Write out size |
678 |
s.writeInt(size); |
679 |
|
680 |
// Write out all elements in the proper order. |
681 |
for (Entry e = header.next; e != header; e = e.next) |
682 |
s.writeObject(e.element); |
683 |
} |
684 |
|
685 |
/** |
686 |
* Reconstitute this <tt>LinkedList</tt> instance from a stream (that is |
687 |
* deserialize it). |
688 |
*/ |
689 |
private synchronized void readObject(java.io.ObjectInputStream s) |
690 |
throws java.io.IOException, ClassNotFoundException { |
691 |
// Read in any hidden serialization magic |
692 |
s.defaultReadObject(); |
693 |
|
694 |
// Read in size |
695 |
int size = s.readInt(); |
696 |
|
697 |
// Initialize header |
698 |
header = new Entry(null, null, null); |
699 |
header.next = header.previous = header; |
700 |
|
701 |
// Read in all elements in the proper order. |
702 |
for (int i=0; i<size; i++) |
703 |
add(s.readObject()); |
704 |
} |
705 |
|
706 |
public Object peek() { |
707 |
if (size==0) |
708 |
return null; |
709 |
return header.previous.element; |
710 |
} |
711 |
|
712 |
public Object element() { |
713 |
if (size==0) |
714 |
throw new NoSuchElementException(); |
715 |
return header.previous.element; |
716 |
} |
717 |
|
718 |
public Object poll() { |
719 |
if (size==0) |
720 |
return null; |
721 |
Object last = header.previous.element; |
722 |
remove(header.previous); |
723 |
return last; |
724 |
} |
725 |
|
726 |
public Object remove() { |
727 |
if (size==0) |
728 |
throw new NoSuchElementException(); |
729 |
Object last = header.previous.element; |
730 |
remove(header.previous); |
731 |
return last; |
732 |
} |
733 |
|
734 |
public boolean offer(Object x) { |
735 |
return add(x); |
736 |
} |
737 |
|
738 |
} |