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	/*
	* Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package sun.awt.util;

	import java.util.AbstractSequentialList;
	import java.util.Collection;
	import java.util.ConcurrentModificationException;
	import java.util.Deque;
	import java.util.Iterator;
	import java.util.List;
	import java.util.ListIterator;
	import java.util.NoSuchElementException;

	/**
	* Linked list implementation of the <tt>List</tt> interface. Implements all
	* optional list operations, and permits all elements (including
	* <tt>null</tt>). In addition to implementing the <tt>List</tt> interface,
	* the <tt>IdentityLinkedList</tt> class provides uniformly named methods to
	* <tt>get</tt>, <tt>remove</tt> and <tt>insert</tt> an element at the
	* beginning and end of the list. These operations allow linked lists to be
	* used as a stack, {@linkplain Queue queue}, or {@linkplain Deque
	* double-ended queue}. <p>
	*
	* The class implements the <tt>Deque</tt> interface, providing
	* first-in-first-out queue operations for <tt>add</tt>,
	* <tt>poll</tt>, along with other stack and deque operations.<p>
	*
	* All of the operations perform as could be expected for a doubly-linked
	* list. Operations that index into the list will traverse the list from
	* the beginning or the end, whichever is closer to the specified index.<p>
	*
	* <p><strong>Note that this implementation is not synchronized.</strong>
	* If multiple threads access a linked list concurrently, and at least
	* one of the threads modifies the list structurally, it <i>must</i> be
	* synchronized externally. (A structural modification is any operation
	* that adds or deletes one or more elements; merely setting the value of
	* an element is not a structural modification.) This is typically
	* accomplished by synchronizing on some object that naturally
	* encapsulates the list.
	*
	* If no such object exists, the list should be "wrapped" using the
	* {@link Collections#synchronizedList Collections.synchronizedList}
	* method. This is best done at creation time, to prevent accidental
	* unsynchronized access to the list:<pre>
	* List list = Collections.synchronizedList(new IdentityLinkedList(...));</pre>
	*
	* <p>The iterators returned by this class's <tt>iterator</tt> and
	* <tt>listIterator</tt> methods are <i>fail-fast</i>: if the list is
	* structurally modified at any time after the iterator is created, in
	* any way except through the Iterator's own <tt>remove</tt> or
	* <tt>add</tt> methods, the iterator will throw a {@link
	* ConcurrentModificationException}. Thus, in the face of concurrent
	* modification, the iterator fails quickly and cleanly, rather than
	* risking arbitrary, non-deterministic behavior at an undetermined
	* time in the future.
	*
	* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
	* as it is, generally speaking, impossible to make any hard guarantees in the
	* presence of unsynchronized concurrent modification. Fail-fast iterators
	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
	* Therefore, it would be wrong to write a program that depended on this
	* exception for its correctness: <i>the fail-fast behavior of iterators
	* should be used only to detect bugs.</i>
	*/

	public class IdentityLinkedList<E>
	extends AbstractSequentialList<E>
	implements List<E>, Deque<E>
	{
	private transient Entry<E> header = new Entry<E>(null, null, null);
	private transient int size = 0;

	/**
	* Constructs an empty list.
	*/
	public IdentityLinkedList() {
	header.next = header.previous = header;
	}

	/**
	* Constructs a list containing the elements of the specified
	* collection, in the order they are returned by the collection's
	* iterator.
	*
	* @param c the collection whose elements are to be placed into this list
	* @throws NullPointerException if the specified collection is null
	*/
	public IdentityLinkedList(Collection<? extends E> c) {
	this();
	addAll(c);
	}

	/**
	* Returns the first element in this list.
	*
	* @return the first element in this list
	* @throws NoSuchElementException if this list is empty
	*/
	public E getFirst() {
	if (size==0)
	throw new NoSuchElementException();

	return header.next.element;
	}

	/**
	* Returns the last element in this list.
	*
	* @return the last element in this list
	* @throws NoSuchElementException if this list is empty
	*/
	public E getLast() {
	if (size==0)
	throw new NoSuchElementException();

	return header.previous.element;
	}

	/**
	* Removes and returns the first element from this list.
	*
	* @return the first element from this list
	* @throws NoSuchElementException if this list is empty
	*/
	public E removeFirst() {
	return remove(header.next);
	}

	/**
	* Removes and returns the last element from this list.
	*
	* @return the last element from this list
	* @throws NoSuchElementException if this list is empty
	*/
	public E removeLast() {
	return remove(header.previous);
	}

	/**
	* Inserts the specified element at the beginning of this list.
	*
	* @param e the element to add
	*/
	public void addFirst(E e) {
	addBefore(e, header.next);
	}

	/**
	* Appends the specified element to the end of this list.
	*
	* <p>This method is equivalent to {@link #add}.
	*
	* @param e the element to add
	*/
	public void addLast(E e) {
	addBefore(e, header);
	}

	/**
	* Returns <tt>true</tt> if this list contains the specified element.
	* More formally, returns <tt>true</tt> if and only if this list contains
	* at least one element <tt>e</tt> such that
	* <tt>(o==null ? e==null : o == e)</tt>.
	*
	* @param o element whose presence in this list is to be tested
	* @return <tt>true</tt> if this list contains the specified element
	*/
	public boolean contains(Object o) {
	return indexOf(o) != -1;
	}

	/**
	* Returns the number of elements in this list.
	*
	* @return the number of elements in this list
	*/
	public int size() {
	return size;
	}

	/**
	* Appends the specified element to the end of this list.
	*
	* <p>This method is equivalent to {@link #addLast}.
	*
	* @param e element to be appended to this list
	* @return <tt>true</tt> (as specified by {@link Collection#add})
	*/
	public boolean add(E e) {
	addBefore(e, header);
	return true;
	}

	/**
	* Removes the first occurrence of the specified element from this list,
	* if it is present. If this list does not contain the element, it is
	* unchanged. More formally, removes the element with the lowest index
	* <tt>i</tt> such that <tt>get(i)==o</tt>
	* (if such an element exists). Returns <tt>true</tt> if this list
	* contained the specified element (or equivalently, if this list
	* changed as a result of the call).
	*
	* @param o element to be removed from this list, if present
	* @return <tt>true</tt> if this list contained the specified element
	*/
	public boolean remove(Object o) {
	for (Entry<E> e = header.next; e != header; e = e.next) {
	if (o == e.element) {
	remove(e);
	return true;
	}
	}
	return false;
	}

	/**
	* Appends all of the elements in the specified collection to the end of
	* this list, in the order that they are returned by the specified
	* collection's iterator. The behavior of this operation is undefined if
	* the specified collection is modified while the operation is in
	* progress. (Note that this will occur if the specified collection is
	* this list, and it's nonempty.)
	*
	* @param c collection containing elements to be added to this list
	* @return <tt>true</tt> if this list changed as a result of the call
	* @throws NullPointerException if the specified collection is null
	*/
	public boolean addAll(Collection<? extends E> c) {
	return addAll(size, c);
	}

	/**
	* Inserts all of the elements in the specified collection into this
	* list, starting at the specified position. Shifts the element
	* currently at that position (if any) and any subsequent elements to
	* the right (increases their indices). The new elements will appear
	* in the list in the order that they are returned by the
	* specified collection's iterator.
	*
	* @param index index at which to insert the first element
	* from the specified collection
	* @param c collection containing elements to be added to this list
	* @return <tt>true</tt> if this list changed as a result of the call
	* @throws IndexOutOfBoundsException {@inheritDoc}
	* @throws NullPointerException if the specified collection is null
	*/
	public boolean addAll(int index, Collection<? extends E> c) {
	if (index < 0 \|\| index > size)
	throw new IndexOutOfBoundsException("Index: "+index+
	", Size: "+size);
	Object[] a = c.toArray();
	int numNew = a.length;
	if (numNew==0)
	return false;
	modCount++;

	Entry<E> successor = (index==size ? header : entry(index));
	Entry<E> predecessor = successor.previous;
	for (int i=0; i<numNew; i++) {
	Entry<E> e = new Entry<E>((E)a[i], successor, predecessor);
	predecessor.next = e;
	predecessor = e;
	}
	successor.previous = predecessor;

	size += numNew;
	return true;
	}

	/**
	* Removes all of the elements from this list.
	*/
	public void clear() {
	Entry<E> e = header.next;
	while (e != header) {
	Entry<E> next = e.next;
	e.next = e.previous = null;
	e.element = null;
	e = next;
	}
	header.next = header.previous = header;
	size = 0;
	modCount++;
	}


	// Positional Access Operations

	/**
	* Returns the element at the specified position in this list.
	*
	* @param index index of the element to return
	* @return the element at the specified position in this list
	* @throws IndexOutOfBoundsException {@inheritDoc}
	*/
	public E get(int index) {
	return entry(index).element;
	}

	/**
	* Replaces the element at the specified position in this list with the
	* specified element.
	*
	* @param index index of the element to replace
	* @param element element to be stored at the specified position
	* @return the element previously at the specified position
	* @throws IndexOutOfBoundsException {@inheritDoc}
	*/
	public E set(int index, E element) {
	Entry<E> e = entry(index);
	E oldVal = e.element;
	e.element = element;
	return oldVal;
	}

	/**
	* Inserts the specified element at the specified position in this list.
	* Shifts the element currently at that position (if any) and any
	* subsequent elements to the right (adds one to their indices).
	*
	* @param index index at which the specified element is to be inserted
	* @param element element to be inserted
	* @throws IndexOutOfBoundsException {@inheritDoc}
	*/
	public void add(int index, E element) {
	addBefore(element, (index==size ? header : entry(index)));
	}

	/**
	* Removes the element at the specified position in this list. Shifts any
	* subsequent elements to the left (subtracts one from their indices).
	* Returns the element that was removed from the list.
	*
	* @param index the index of the element to be removed
	* @return the element previously at the specified position
	* @throws IndexOutOfBoundsException {@inheritDoc}
	*/
	public E remove(int index) {
	return remove(entry(index));
	}

	/**
	* Returns the indexed entry.
	*/
	private Entry<E> entry(int index) {
	if (index < 0 \|\| index >= size)
	throw new IndexOutOfBoundsException("Index: "+index+
	", Size: "+size);
	Entry<E> e = header;
	if (index < (size >> 1)) {
	for (int i = 0; i <= index; i++)
	e = e.next;
	} else {
	for (int i = size; i > index; i--)
	e = e.previous;
	}
	return e;
	}


	// Search Operations

	/**
	* Returns the index of the first occurrence of the specified element
	* in this list, or -1 if this list does not contain the element.
	* More formally, returns the lowest index <tt>i</tt> such that
	* <tt>get(i)==o</tt>,
	* or -1 if there is no such index.
	*
	* @param o element to search for
	* @return the index of the first occurrence of the specified element in
	* this list, or -1 if this list does not contain the element
	*/
	public int indexOf(Object o) {
	int index = 0;
	for (Entry e = header.next; e != header; e = e.next) {
	if (o == e.element) {
	return index;
	}
	index++;
	}
	return -1;
	}

	/**
	* Returns the index of the last occurrence of the specified element
	* in this list, or -1 if this list does not contain the element.
	* More formally, returns the highest index <tt>i</tt> such that
	* <tt>get(i)==o</tt>,
	* or -1 if there is no such index.
	*
	* @param o element to search for
	* @return the index of the last occurrence of the specified element in
	* this list, or -1 if this list does not contain the element
	*/
	public int lastIndexOf(Object o) {
	int index = size;
	for (Entry e = header.previous; e != header; e = e.previous) {
	index--;
	if (o == e.element) {
	return index;
	}
	}
	return -1;
	}

	// Queue operations.

	/**
	* Retrieves, but does not remove, the head (first element) of this list.
	* @return the head of this list, or <tt>null</tt> if this list is empty
	* @since 1.5
	*/
	public E peek() {
	if (size==0)
	return null;
	return getFirst();
	}

	/**
	* Retrieves, but does not remove, the head (first element) of this list.
	* @return the head of this list
	* @throws NoSuchElementException if this list is empty
	* @since 1.5
	*/
	public E element() {
	return getFirst();
	}

	/**
	* Retrieves and removes the head (first element) of this list
	* @return the head of this list, or <tt>null</tt> if this list is empty
	* @since 1.5
	*/
	public E poll() {
	if (size==0)
	return null;
	return removeFirst();
	}

	/**
	* Retrieves and removes the head (first element) of this list.
	*
	* @return the head of this list
	* @throws NoSuchElementException if this list is empty
	* @since 1.5
	*/
	public E remove() {
	return removeFirst();
	}

	/**
	* Adds the specified element as the tail (last element) of this list.
	*
	* @param e the element to add
	* @return <tt>true</tt> (as specified by {@link Queue#offer})
	* @since 1.5
	*/
	public boolean offer(E e) {
	return add(e);
	}

	// Deque operations
	/**
	* Inserts the specified element at the front of this list.
	*
	* @param e the element to insert
	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
	* @since 1.6
	*/
	public boolean offerFirst(E e) {
	addFirst(e);
	return true;
	}

	/**
	* Inserts the specified element at the end of this list.
	*
	* @param e the element to insert
	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
	* @since 1.6
	*/
	public boolean offerLast(E e) {
	addLast(e);
	return true;
	}

	/**
	* Retrieves, but does not remove, the first element of this list,
	* or returns <tt>null</tt> if this list is empty.
	*
	* @return the first element of this list, or <tt>null</tt>
	* if this list is empty
	* @since 1.6
	*/
	public E peekFirst() {
	if (size==0)
	return null;
	return getFirst();
	}

	/**
	* Retrieves, but does not remove, the last element of this list,
	* or returns <tt>null</tt> if this list is empty.
	*
	* @return the last element of this list, or <tt>null</tt>
	* if this list is empty
	* @since 1.6
	*/
	public E peekLast() {
	if (size==0)
	return null;
	return getLast();
	}

	/**
	* Retrieves and removes the first element of this list,
	* or returns <tt>null</tt> if this list is empty.
	*
	* @return the first element of this list, or <tt>null</tt> if
	* this list is empty
	* @since 1.6
	*/
	public E pollFirst() {
	if (size==0)
	return null;
	return removeFirst();
	}

	/**
	* Retrieves and removes the last element of this list,
	* or returns <tt>null</tt> if this list is empty.
	*
	* @return the last element of this list, or <tt>null</tt> if
	* this list is empty
	* @since 1.6
	*/
	public E pollLast() {
	if (size==0)
	return null;
	return removeLast();
	}

	/**
	* Pushes an element onto the stack represented by this list. In other
	* words, inserts the element at the front of this list.
	*
	* <p>This method is equivalent to {@link #addFirst}.
	*
	* @param e the element to push
	* @since 1.6
	*/
	public void push(E e) {
	addFirst(e);
	}

	/**
	* Pops an element from the stack represented by this list. In other
	* words, removes and returns the first element of this list.
	*
	* <p>This method is equivalent to {@link #removeFirst()}.
	*
	* @return the element at the front of this list (which is the top
	* of the stack represented by this list)
	* @throws NoSuchElementException if this list is empty
	* @since 1.6
	*/
	public E pop() {
	return removeFirst();
	}

	/**
	* Removes the first occurrence of the specified element in this
	* list (when traversing the list from head to tail). If the list
	* does not contain the element, it is unchanged.
	*
	* @param o element to be removed from this list, if present
	* @return <tt>true</tt> if the list contained the specified element
	* @since 1.6
	*/
	public boolean removeFirstOccurrence(Object o) {
	return remove(o);
	}

	/**
	* Removes the last occurrence of the specified element in this
	* list (when traversing the list from head to tail). If the list
	* does not contain the element, it is unchanged.
	*
	* @param o element to be removed from this list, if present
	* @return <tt>true</tt> if the list contained the specified element
	* @since 1.6
	*/
	public boolean removeLastOccurrence(Object o) {
	for (Entry<E> e = header.previous; e != header; e = e.previous) {
	if (o == e.element) {
	remove(e);
	return true;
	}
	}
	return false;
	}

	/**
	* Returns a list-iterator of the elements in this list (in proper
	* sequence), starting at the specified position in the list.
	* Obeys the general contract of <tt>List.listIterator(int)</tt>.<p>
	*
	* The list-iterator is <i>fail-fast</i>: if the list is structurally
	* modified at any time after the Iterator is created, in any way except
	* through the list-iterator's own <tt>remove</tt> or <tt>add</tt>
	* methods, the list-iterator will throw a
	* <tt>ConcurrentModificationException</tt>. Thus, in the face of
	* concurrent modification, the iterator fails quickly and cleanly, rather
	* than risking arbitrary, non-deterministic behavior at an undetermined
	* time in the future.
	*
	* @param index index of the first element to be returned from the
	* list-iterator (by a call to <tt>next</tt>)
	* @return a ListIterator of the elements in this list (in proper
	* sequence), starting at the specified position in the list
	* @throws IndexOutOfBoundsException {@inheritDoc}
	* @see List#listIterator(int)
	*/
	public ListIterator<E> listIterator(int index) {
	return new ListItr(index);
	}

	private class ListItr implements ListIterator<E> {
	private Entry<E> lastReturned = header;
	private Entry<E> next;
	private int nextIndex;
	private int expectedModCount = modCount;

	ListItr(int index) {
	if (index < 0 \|\| index > size)
	throw new IndexOutOfBoundsException("Index: "+index+
	", Size: "+size);
	if (index < (size >> 1)) {
	next = header.next;
	for (nextIndex=0; nextIndex<index; nextIndex++)
	next = next.next;
	} else {
	next = header;
	for (nextIndex=size; nextIndex>index; nextIndex--)
	next = next.previous;
	}
	}

	public boolean hasNext() {
	return nextIndex != size;
	}

	public E next() {
	checkForComodification();
	if (nextIndex == size)
	throw new NoSuchElementException();

	lastReturned = next;
	next = next.next;
	nextIndex++;
	return lastReturned.element;
	}

	public boolean hasPrevious() {
	return nextIndex != 0;
	}

	public E previous() {
	if (nextIndex == 0)
	throw new NoSuchElementException();

	lastReturned = next = next.previous;
	nextIndex--;
	checkForComodification();
	return lastReturned.element;
	}

	public int nextIndex() {
	return nextIndex;
	}

	public int previousIndex() {
	return nextIndex-1;
	}

	public void remove() {
	checkForComodification();
	Entry<E> lastNext = lastReturned.next;
	try {
	IdentityLinkedList.this.remove(lastReturned);
	} catch (NoSuchElementException e) {
	throw new IllegalStateException();
	}
	if (next==lastReturned)
	next = lastNext;
	else
	nextIndex--;
	lastReturned = header;
	expectedModCount++;
	}

	public void set(E e) {
	if (lastReturned == header)
	throw new IllegalStateException();
	checkForComodification();
	lastReturned.element = e;
	}

	public void add(E e) {
	checkForComodification();
	lastReturned = header;
	addBefore(e, next);
	nextIndex++;
	expectedModCount++;
	}

	final void checkForComodification() {
	if (modCount != expectedModCount)
	throw new ConcurrentModificationException();
	}
	}

	private static class Entry<E> {
	E element;
	Entry<E> next;
	Entry<E> previous;

	Entry(E element, Entry<E> next, Entry<E> previous) {
	this.element = element;
	this.next = next;
	this.previous = previous;
	}
	}

	private Entry<E> addBefore(E e, Entry<E> entry) {
	Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);
	newEntry.previous.next = newEntry;
	newEntry.next.previous = newEntry;
	size++;
	modCount++;
	return newEntry;
	}

	private E remove(Entry<E> e) {
	if (e == header)
	throw new NoSuchElementException();

	E result = e.element;
	e.previous.next = e.next;
	e.next.previous = e.previous;
	e.next = e.previous = null;
	e.element = null;
	size--;
	modCount++;
	return result;
	}

	/**
	* @since 1.6
	*/
	public Iterator<E> descendingIterator() {
	return new DescendingIterator();
	}

	/** Adapter to provide descending iterators via ListItr.previous */
	private class DescendingIterator implements Iterator {
	final ListItr itr = new ListItr(size());
	public boolean hasNext() {
	return itr.hasPrevious();
	}
	public E next() {
	return itr.previous();
	}
	public void remove() {
	itr.remove();
	}
	}

	/**
	* Returns an array containing all of the elements in this list
	* in proper sequence (from first to last element).
	*
	* <p>The returned array will be "safe" in that no references to it are
	* maintained by this list. (In other words, this method must allocate
	* a new array). The caller is thus free to modify the returned array.
	*
	* <p>This method acts as bridge between array-based and collection-based
	* APIs.
	*
	* @return an array containing all of the elements in this list
	* in proper sequence
	*/
	public Object[] toArray() {
	Object[] result = new Object[size];
	int i = 0;
	for (Entry<E> e = header.next; e != header; e = e.next)
	result[i++] = e.element;
	return result;
	}

	/**
	* Returns an array containing all of the elements in this list in
	* proper sequence (from first to last element); the runtime type of
	* the returned array is that of the specified array. If the list fits
	* in the specified array, it is returned therein. Otherwise, a new
	* array is allocated with the runtime type of the specified array and
	* the size of this list.
	*
	* <p>If the list fits in the specified array with room to spare (i.e.,
	* the array has more elements than the list), the element in the array
	* immediately following the end of the list is set to <tt>null</tt>.
	* (This is useful in determining the length of the list <i>only</i> if
	* the caller knows that the list does not contain any null elements.)
	*
	* <p>Like the {@link #toArray()} method, this method acts as bridge between
	* array-based and collection-based APIs. Further, this method allows
	* precise control over the runtime type of the output array, and may,
	* under certain circumstances, be used to save allocation costs.
	*
	* <p>Suppose <tt>x</tt> is a list known to contain only strings.
	* The following code can be used to dump the list into a newly
	* allocated array of <tt>String</tt>:
	*
	* <pre>
	* String[] y = x.toArray(new String[0]);</pre>
	*
	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
	* <tt>toArray()</tt>.
	*
	* @param a the array into which the elements of the list are to
	* be stored, if it is big enough; otherwise, a new array of the
	* same runtime type is allocated for this purpose.
	* @return an array containing the elements of the list
	* @throws ArrayStoreException if the runtime type of the specified array
	* is not a supertype of the runtime type of every element in
	* this list
	* @throws NullPointerException if the specified array is null
	*/
	public <T> T[] toArray(T[] a) {
	if (a.length < size)
	a = (T[])java.lang.reflect.Array.newInstance(
	a.getClass().getComponentType(), size);
	int i = 0;
	Object[] result = a;
	for (Entry<E> e = header.next; e != header; e = e.next)
	result[i++] = e.element;

	if (a.length > size)
	a[size] = null;

	return a;
	}
	}

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