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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) { |
208 |
if (o==null) { |
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for (Entry e = header.next; e != header; e = e.next) { |
210 |
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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*/ |
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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. |
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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. |
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) { |
261 |
if (index < 0 || index >= size) |
262 |
throw new IndexOutOfBoundsException(); |
263 |
else |
264 |
return false; |
265 |
} |
266 |
modCount++; |
267 |
|
268 |
Entry successor = (index==size ? header : entry(index)); |
269 |
Entry predecessor = successor.previous; |
270 |
Iterator it = c.iterator(); |
271 |
for (int i=0; i<numNew; i++) { |
272 |
Entry e = new Entry(it.next(), successor, predecessor); |
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predecessor.next = e; |
274 |
predecessor = e; |
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} |
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successor.previous = predecessor; |
277 |
|
278 |
size += numNew; |
279 |
return true; |
280 |
} |
281 |
|
282 |
/** |
283 |
* Removes all of the elements from this list. |
284 |
*/ |
285 |
public void clear() { |
286 |
modCount++; |
287 |
header.next = header.previous = header; |
288 |
size = 0; |
289 |
} |
290 |
|
291 |
|
292 |
// Positional Access Operations |
293 |
|
294 |
/** |
295 |
* Returns the element at the specified position in this list. |
296 |
* |
297 |
* @param index index of element to return. |
298 |
* @return the element at the specified position in this list. |
299 |
* |
300 |
* @throws IndexOutOfBoundsException if the specified index is is out of |
301 |
* range (<tt>index < 0 || index >= size()</tt>). |
302 |
*/ |
303 |
public Object get(int index) { |
304 |
return entry(index).element; |
305 |
} |
306 |
|
307 |
/** |
308 |
* Replaces the element at the specified position in this list with the |
309 |
* specified element. |
310 |
* |
311 |
* @param index index of element to replace. |
312 |
* @param element element to be stored at the specified position. |
313 |
* @return the element previously at the specified position. |
314 |
* @throws IndexOutOfBoundsException if the specified index is out of |
315 |
* range (<tt>index < 0 || index >= size()</tt>). |
316 |
*/ |
317 |
public Object set(int index, Object element) { |
318 |
Entry e = entry(index); |
319 |
Object oldVal = e.element; |
320 |
e.element = element; |
321 |
return oldVal; |
322 |
} |
323 |
|
324 |
/** |
325 |
* Inserts the specified element at the specified position in this list. |
326 |
* Shifts the element currently at that position (if any) and any |
327 |
* subsequent elements to the right (adds one to their indices). |
328 |
* |
329 |
* @param index index at which the specified element is to be inserted. |
330 |
* @param element element to be inserted. |
331 |
* |
332 |
* @throws IndexOutOfBoundsException if the specified index is out of |
333 |
* range (<tt>index < 0 || index > size()</tt>). |
334 |
*/ |
335 |
public void add(int index, Object element) { |
336 |
addBefore(element, (index==size ? header : entry(index))); |
337 |
} |
338 |
|
339 |
/** |
340 |
* Removes the element at the specified position in this list. Shifts any |
341 |
* subsequent elements to the left (subtracts one from their indices). |
342 |
* Returns the element that was removed from the list. |
343 |
* |
344 |
* @param index the index of the element to removed. |
345 |
* @return the element previously at the specified position. |
346 |
* |
347 |
* @throws IndexOutOfBoundsException if the specified index is out of |
348 |
* range (<tt>index < 0 || index >= size()</tt>). |
349 |
*/ |
350 |
public Object remove(int index) { |
351 |
Entry e = entry(index); |
352 |
remove(e); |
353 |
return e.element; |
354 |
} |
355 |
|
356 |
/** |
357 |
* Return the indexed entry. |
358 |
*/ |
359 |
private Entry entry(int index) { |
360 |
if (index < 0 || index >= size) |
361 |
throw new IndexOutOfBoundsException("Index: "+index+ |
362 |
", Size: "+size); |
363 |
Entry e = header; |
364 |
if (index < (size >> 1)) { |
365 |
for (int i = 0; i <= index; i++) |
366 |
e = e.next; |
367 |
} else { |
368 |
for (int i = size; i > index; i--) |
369 |
e = e.previous; |
370 |
} |
371 |
return e; |
372 |
} |
373 |
|
374 |
|
375 |
// Search Operations |
376 |
|
377 |
/** |
378 |
* Returns the index in this list of the first occurrence of the |
379 |
* specified element, or -1 if the List does not contain this |
380 |
* element. More formally, returns the lowest index i such that |
381 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, or -1 if |
382 |
* there is no such index. |
383 |
* |
384 |
* @param o element to search for. |
385 |
* @return the index in this list of the first occurrence of the |
386 |
* specified element, or -1 if the list does not contain this |
387 |
* element. |
388 |
*/ |
389 |
public int indexOf(Object o) { |
390 |
int index = 0; |
391 |
if (o==null) { |
392 |
for (Entry e = header.next; e != header; e = e.next) { |
393 |
if (e.element==null) |
394 |
return index; |
395 |
index++; |
396 |
} |
397 |
} else { |
398 |
for (Entry e = header.next; e != header; e = e.next) { |
399 |
if (o.equals(e.element)) |
400 |
return index; |
401 |
index++; |
402 |
} |
403 |
} |
404 |
return -1; |
405 |
} |
406 |
|
407 |
/** |
408 |
* Returns the index in this list of the last occurrence of the |
409 |
* specified element, or -1 if the list does not contain this |
410 |
* element. More formally, returns the highest index i such that |
411 |
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, or -1 if |
412 |
* there is no such index. |
413 |
* |
414 |
* @param o element to search for. |
415 |
* @return the index in this list of the last occurrence of the |
416 |
* specified element, or -1 if the list does not contain this |
417 |
* element. |
418 |
*/ |
419 |
public int lastIndexOf(Object o) { |
420 |
int index = size; |
421 |
if (o==null) { |
422 |
for (Entry e = header.previous; e != header; e = e.previous) { |
423 |
index--; |
424 |
if (e.element==null) |
425 |
return index; |
426 |
} |
427 |
} else { |
428 |
for (Entry e = header.previous; e != header; e = e.previous) { |
429 |
index--; |
430 |
if (o.equals(e.element)) |
431 |
return index; |
432 |
} |
433 |
} |
434 |
return -1; |
435 |
} |
436 |
|
437 |
/** |
438 |
* Returns a list-iterator of the elements in this list (in proper |
439 |
* sequence), starting at the specified position in the list. |
440 |
* Obeys the general contract of <tt>List.listIterator(int)</tt>.<p> |
441 |
* |
442 |
* The list-iterator is <i>fail-fast</i>: if the list is structurally |
443 |
* modified at any time after the Iterator is created, in any way except |
444 |
* through the list-iterator's own <tt>remove</tt> or <tt>add</tt> |
445 |
* methods, the list-iterator will throw a |
446 |
* <tt>ConcurrentModificationException</tt>. Thus, in the face of |
447 |
* concurrent modification, the iterator fails quickly and cleanly, rather |
448 |
* than risking arbitrary, non-deterministic behavior at an undetermined |
449 |
* time in the future. |
450 |
* |
451 |
* @param index index of first element to be returned from the |
452 |
* list-iterator (by a call to <tt>next</tt>). |
453 |
* @return a ListIterator of the elements in this list (in proper |
454 |
* sequence), starting at the specified position in the list. |
455 |
* @throws IndexOutOfBoundsException if index is out of range |
456 |
* (<tt>index < 0 || index > size()</tt>). |
457 |
* @see java.util.List#listIterator(int) |
458 |
*/ |
459 |
public ListIterator listIterator(int index) { |
460 |
return new ListItr(index); |
461 |
} |
462 |
|
463 |
private class ListItr implements ListIterator { |
464 |
private Entry lastReturned = header; |
465 |
private Entry next; |
466 |
private int nextIndex; |
467 |
private int expectedModCount = modCount; |
468 |
|
469 |
ListItr(int index) { |
470 |
if (index < 0 || index > size) |
471 |
throw new IndexOutOfBoundsException("Index: "+index+ |
472 |
", Size: "+size); |
473 |
if (index < (size >> 1)) { |
474 |
next = header.next; |
475 |
for (nextIndex=0; nextIndex<index; nextIndex++) |
476 |
next = next.next; |
477 |
} else { |
478 |
next = header; |
479 |
for (nextIndex=size; nextIndex>index; nextIndex--) |
480 |
next = next.previous; |
481 |
} |
482 |
} |
483 |
|
484 |
public boolean hasNext() { |
485 |
return nextIndex != size; |
486 |
} |
487 |
|
488 |
public Object next() { |
489 |
checkForComodification(); |
490 |
if (nextIndex == size) |
491 |
throw new NoSuchElementException(); |
492 |
|
493 |
lastReturned = next; |
494 |
next = next.next; |
495 |
nextIndex++; |
496 |
return lastReturned.element; |
497 |
} |
498 |
|
499 |
public boolean hasPrevious() { |
500 |
return nextIndex != 0; |
501 |
} |
502 |
|
503 |
public Object previous() { |
504 |
if (nextIndex == 0) |
505 |
throw new NoSuchElementException(); |
506 |
|
507 |
lastReturned = next = next.previous; |
508 |
nextIndex--; |
509 |
checkForComodification(); |
510 |
return lastReturned.element; |
511 |
} |
512 |
|
513 |
public int nextIndex() { |
514 |
return nextIndex; |
515 |
} |
516 |
|
517 |
public int previousIndex() { |
518 |
return nextIndex-1; |
519 |
} |
520 |
|
521 |
public void remove() { |
522 |
checkForComodification(); |
523 |
try { |
524 |
LinkedList.this.remove(lastReturned); |
525 |
} catch (NoSuchElementException e) { |
526 |
throw new IllegalStateException(); |
527 |
} |
528 |
if (next==lastReturned) |
529 |
next = lastReturned.next; |
530 |
else |
531 |
nextIndex--; |
532 |
lastReturned = header; |
533 |
expectedModCount++; |
534 |
} |
535 |
|
536 |
public void set(Object o) { |
537 |
if (lastReturned == header) |
538 |
throw new IllegalStateException(); |
539 |
checkForComodification(); |
540 |
lastReturned.element = o; |
541 |
} |
542 |
|
543 |
public void add(Object o) { |
544 |
checkForComodification(); |
545 |
lastReturned = header; |
546 |
addBefore(o, next); |
547 |
nextIndex++; |
548 |
expectedModCount++; |
549 |
} |
550 |
|
551 |
final void checkForComodification() { |
552 |
if (modCount != expectedModCount) |
553 |
throw new ConcurrentModificationException(); |
554 |
} |
555 |
} |
556 |
|
557 |
private static class Entry { |
558 |
Object element; |
559 |
Entry next; |
560 |
Entry previous; |
561 |
|
562 |
Entry(Object element, Entry next, Entry previous) { |
563 |
this.element = element; |
564 |
this.next = next; |
565 |
this.previous = previous; |
566 |
} |
567 |
} |
568 |
|
569 |
private Entry addBefore(Object o, Entry e) { |
570 |
Entry newEntry = new Entry(o, e, e.previous); |
571 |
newEntry.previous.next = newEntry; |
572 |
newEntry.next.previous = newEntry; |
573 |
size++; |
574 |
modCount++; |
575 |
return newEntry; |
576 |
} |
577 |
|
578 |
private void remove(Entry e) { |
579 |
if (e == header) |
580 |
throw new NoSuchElementException(); |
581 |
|
582 |
e.previous.next = e.next; |
583 |
e.next.previous = e.previous; |
584 |
size--; |
585 |
modCount++; |
586 |
} |
587 |
|
588 |
/** |
589 |
* Returns a shallow copy of this <tt>LinkedList</tt>. (The elements |
590 |
* themselves are not cloned.) |
591 |
* |
592 |
* @return a shallow copy of this <tt>LinkedList</tt> instance. |
593 |
*/ |
594 |
public Object clone() { |
595 |
LinkedList clone = null; |
596 |
try { |
597 |
clone = (LinkedList)super.clone(); |
598 |
} catch (CloneNotSupportedException e) { |
599 |
throw new InternalError(); |
600 |
} |
601 |
|
602 |
// Put clone into "virgin" state |
603 |
clone.header = new Entry(null, null, null); |
604 |
clone.header.next = clone.header.previous = clone.header; |
605 |
clone.size = 0; |
606 |
clone.modCount = 0; |
607 |
|
608 |
// Initialize clone with our elements |
609 |
for (Entry e = header.next; e != header; e = e.next) |
610 |
clone.add(e.element); |
611 |
|
612 |
return clone; |
613 |
} |
614 |
|
615 |
/** |
616 |
* Returns an array containing all of the elements in this list |
617 |
* in the correct order. |
618 |
* |
619 |
* @return an array containing all of the elements in this list |
620 |
* in the correct order. |
621 |
*/ |
622 |
public Object[] toArray() { |
623 |
Object[] result = new Object[size]; |
624 |
int i = 0; |
625 |
for (Entry e = header.next; e != header; e = e.next) |
626 |
result[i++] = e.element; |
627 |
return result; |
628 |
} |
629 |
|
630 |
/** |
631 |
* Returns an array containing all of the elements in this list in |
632 |
* the correct order; the runtime type of the returned array is that of |
633 |
* the specified array. If the list fits in the specified array, it |
634 |
* is returned therein. Otherwise, a new array is allocated with the |
635 |
* runtime type of the specified array and the size of this list.<p> |
636 |
* |
637 |
* If the list fits in the specified array with room to spare |
638 |
* (i.e., the array has more elements than the list), |
639 |
* the element in the array immediately following the end of the |
640 |
* collection is set to null. This is useful in determining the length |
641 |
* of the list <i>only</i> if the caller knows that the list |
642 |
* does not contain any null elements. |
643 |
* |
644 |
* @param a the array into which the elements of the list are to |
645 |
* be stored, if it is big enough; otherwise, a new array of the |
646 |
* same runtime type is allocated for this purpose. |
647 |
* @return an array containing the elements of the list. |
648 |
* @throws ArrayStoreException if the runtime type of a is not a |
649 |
* supertype of the runtime type of every element in this list. |
650 |
* @throws NullPointerException if the specified array is null. |
651 |
*/ |
652 |
public Object[] toArray(Object a[]) { |
653 |
if (a.length < size) |
654 |
a = (Object[])java.lang.reflect.Array.newInstance( |
655 |
a.getClass().getComponentType(), size); |
656 |
int i = 0; |
657 |
for (Entry e = header.next; e != header; e = e.next) |
658 |
a[i++] = e.element; |
659 |
|
660 |
if (a.length > size) |
661 |
a[size] = null; |
662 |
|
663 |
return a; |
664 |
} |
665 |
|
666 |
private static final long serialVersionUID = 876323262645176354L; |
667 |
|
668 |
/** |
669 |
* Save the state of this <tt>LinkedList</tt> instance to a stream (that |
670 |
* is, serialize it). |
671 |
* |
672 |
* @serialData The size of the list (the number of elements it |
673 |
* contains) is emitted (int), followed by all of its |
674 |
* elements (each an Object) in the proper order. |
675 |
*/ |
676 |
private synchronized void writeObject(java.io.ObjectOutputStream s) |
677 |
throws java.io.IOException { |
678 |
// Write out any hidden serialization magic |
679 |
s.defaultWriteObject(); |
680 |
|
681 |
// Write out size |
682 |
s.writeInt(size); |
683 |
|
684 |
// Write out all elements in the proper order. |
685 |
for (Entry e = header.next; e != header; e = e.next) |
686 |
s.writeObject(e.element); |
687 |
} |
688 |
|
689 |
/** |
690 |
* Reconstitute this <tt>LinkedList</tt> instance from a stream (that is |
691 |
* deserialize it). |
692 |
*/ |
693 |
private synchronized void readObject(java.io.ObjectInputStream s) |
694 |
throws java.io.IOException, ClassNotFoundException { |
695 |
// Read in any hidden serialization magic |
696 |
s.defaultReadObject(); |
697 |
|
698 |
// Read in size |
699 |
int size = s.readInt(); |
700 |
|
701 |
// Initialize header |
702 |
header = new Entry(null, null, null); |
703 |
header.next = header.previous = header; |
704 |
|
705 |
// Read in all elements in the proper order. |
706 |
for (int i=0; i<size; i++) |
707 |
add(s.readObject()); |
708 |
} |
709 |
|
710 |
public Object peek() { |
711 |
if (size==0) |
712 |
return null; |
713 |
return getFirst(); |
714 |
} |
715 |
|
716 |
public Object element() { |
717 |
return getFirst(); |
718 |
} |
719 |
|
720 |
public Object poll() { |
721 |
if (size==0) |
722 |
return null; |
723 |
return removeFirst(); |
724 |
} |
725 |
|
726 |
public Object remove() { |
727 |
return removeFirst(); |
728 |
} |
729 |
|
730 |
public boolean offer(Object x) { |
731 |
return add(x); |
732 |
} |
733 |
|
734 |
} |