585 lines
15 KiB
Java
585 lines
15 KiB
Java
/* LinkedList.java -- Linked list implementation of the List interface
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Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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As a special exception, if you link this library with other files to
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produce an executable, this library does not by itself cause the
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resulting executable to be covered by the GNU General Public License.
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This exception does not however invalidate any other reasons why the
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executable file might be covered by the GNU General Public License. */
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package java.util;
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import java.io.Serializable;
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import java.io.ObjectOutputStream;
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import java.io.ObjectInputStream;
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import java.io.IOException;
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// TO DO:
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// ~ Doc comment for the class.
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// ~ Doc comments for the non-list methods.
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// ~ Some commenting on the Backing API and other general implementation notes.
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/**
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* Linked list implementation of the List interface.
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*/
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public class LinkedList extends AbstractSequentialList
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implements Serializable, Cloneable
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{
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static final long serialVersionUID = 876323262645176354L;
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/**
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* An Entry containing the head (in the next field) and the tail (in the
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* previous field) of the list. The data field is null. If the list is empty,
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* both the head and the tail point to ends itself.
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*/
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transient Entry ends = new Entry();
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/**
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* The current length of the list.
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*/
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transient int size = 0;
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/**
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* Class to represent an entry in the list. Holds a single element.
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*/
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private static class Entry {
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/**
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* The list element.
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*/
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Object data = null;
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/**
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* The next entry in the list. If this is the last entry in the list, the
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* ends field of the list is held here.
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*/
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Entry next;
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/**
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* The previous entry in the list. If this is the first entry in the list,
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* the ends field of the list is held here.
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*/
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Entry previous;
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/**
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* Create an entry with given data and linkage.
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*/
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Entry(Object d, Entry n, Entry p) {
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data = d;
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next = n;
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previous = p;
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}
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/**
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* Create an entry with no data and linking to itself, for use as the ends
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* field of the list.
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*/
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Entry() {
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next = previous = this;
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}
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/**
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* Remove this entry.
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*/
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Object remove() {
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previous.next = next;
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next.previous = previous;
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return data;
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}
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}
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private static interface Backing {
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void checkMod(int known);
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void upMod();
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void incSize(int by);
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void decSize(int by);
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}
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private final Backing back = new Backing() {
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public void checkMod(int known) {
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if (known != modCount) {
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throw new ConcurrentModificationException();
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}
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}
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public void upMod() {
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modCount++;
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}
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public void incSize(int by) {
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size += by;
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}
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public void decSize(int by) {
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size -= by;
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}
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};
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/** A ListIterator over the list. This class keeps track of its
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* position in the list, the size of the list, and the two list
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* entries it is between. This enables it to be used identically
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* for both the list itself and a sublist of the list.
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*/
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private static class Iter implements ListIterator {
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/**
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* The index of the element that will be returned by next().
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*/
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int pos;
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/**
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* The size of the backing list.
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*/
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int size;
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/**
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* The entry containing the element that will be returned by next().
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*/
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Entry next;
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/**
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* The entry containing the element that will be returned by previous().
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*/
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Entry previous;
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/**
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* The entry that will be affected by remove() or set().
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*/
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Entry recent;
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/**
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* The known value of the modCount of the backing list.
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*/
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int knownMod;
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private final Backing b;
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/**
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* Create a new Iter starting at a given Entry within the list, at a given
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* position, in a list of given size.
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*
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* @param index the index to begin iteration.
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* @exception IndexOutOfBoundsException if index < 0 || index > size.
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*/
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Iter(Backing backing, Entry n, int index, int s, int modCount) {
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b = backing;
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pos = index;
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size = s;
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next = n;
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previous = n.previous;
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knownMod = modCount;
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}
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public int nextIndex() {
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b.checkMod(knownMod);
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return pos;
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}
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public int previousIndex() {
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b.checkMod(knownMod);
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return pos - 1;
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}
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public boolean hasNext() {
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b.checkMod(knownMod);
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return pos < size;
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}
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public boolean hasPrevious() {
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b.checkMod(knownMod);
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return pos > 0;
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}
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public Object next() {
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b.checkMod(knownMod);
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if (pos >= size) {
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throw new NoSuchElementException();
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} else {
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pos++;
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recent = previous = next;
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next = recent.next;
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return recent.data;
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}
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}
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public Object previous() {
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b.checkMod(knownMod);
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if (pos <= 0) {
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throw new NoSuchElementException();
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} else {
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pos--;
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recent = next = previous;
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previous = recent.previous;
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return recent.data;
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}
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}
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public void remove() {
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b.checkMod(knownMod);
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if (recent == null) {
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throw new IllegalStateException();
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}
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// Adjust the position to before the removed element
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if (recent == previous) pos--;
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// Could use recent.remove() but this way is quicker, and also correctly
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// fixes next and previous.
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next = recent.previous.next = recent.next;
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previous = recent.next.previous = recent.previous;
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size--;
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b.decSize(1);
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knownMod++;
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b.upMod();
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recent = null;
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}
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public void add(Object o) {
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b.checkMod(knownMod);
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previous.next = next.previous = new Entry(o, next, previous);
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// New for 1.2RC1 - the semantics changed so that the iterator is
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// positioned *after* the new element.
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previous = previous.next;
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pos++;
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size++;
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b.incSize(1);
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knownMod++;
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b.upMod();
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recent = null;
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}
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public void set(Object o) {
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b.checkMod(knownMod);
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if (recent == null) {
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throw new IllegalStateException();
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}
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recent.data = o;
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}
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}
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/**
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* Obtain the Entry at a given position in a list. This method of course
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* takes linear time, but it is intelligent enough to take the shorter of the
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* paths to get to the Entry required. This implies that the first or last
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* entry in the list is obtained in constant time, which is a very desirable
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* property.
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* For speed and flexibility in which ranges are valid, range checking is not
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* done in this method, and if n is outside the range -1 <= n <= size, the
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* result will be wrong (but no exception will be thrown).
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* Note that you *can* obtain entries at position -1 and size, which are
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* equal to prehead and posttail respectively.
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* This method is static so that it can also be used in subList.
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*
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* @param n the number of the entry to get.
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* @param size the size of the list to get the entry in.
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* @param head the entry before the first element of the list (usually ends).
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* @param tail the entry after the last element of the list (usually ends).
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*/
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static Entry getEntry(int n, int size, Entry head, Entry tail) {
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// n less than size/2, iterate from start
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if (n < size >> 1) {
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while (n-- >= 0) {
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head = head.next;
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}
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return head;
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// n greater than size/2, iterate from end
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} else {
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while (++n <= size) {
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tail = tail.previous;
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}
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return tail;
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}
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}
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/**
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* Create an empty linked list.
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*/
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public LinkedList() {
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super();
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}
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/**
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* Create a linked list containing the elements, in order, of a given
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* collection.
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*
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* @param c the collection to populate this list from.
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*/
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public LinkedList(Collection c) {
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super();
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// Note: addAll could be made slightly faster, but not enough so to justify
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// re-implementing it from scratch. It is just a matter of a relatively
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// small constant factor.
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addAll(c);
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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 ends.next.data;
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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 ends.previous.data;
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}
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public Object removeFirst() {
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if (size == 0) {
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throw new NoSuchElementException();
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}
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size--;
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modCount++;
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return ends.next.remove();
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}
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public Object removeLast() {
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if (size == 0) {
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throw new NoSuchElementException();
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}
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size--;
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modCount++;
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return ends.previous.remove();
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}
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public void addFirst(Object o) {
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ends.next.previous = ends.next = new Entry(o, ends.next, ends);
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size++;
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modCount++;
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}
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public void addLast(Object o) {
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ends.previous.next = ends.previous = new Entry(o, ends, ends.previous);
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size++;
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modCount++;
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}
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/**
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* Obtain the number of elements currently in this list.
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*
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* @returns the number of elements currently 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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* Remove a range of elements from this list.
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*
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* @param fromIndex the index, inclusive, to remove from.
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* @param toIndex the index, exclusive, to remove to.
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* @exception IndexOutOfBoundsException if fromIndex > toIndex || fromIndex <
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* 0 || toIndex > size().
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*/
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// Note: normally removeRange is provided to allow efficient ways to
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// implement clear() on subLists. However, in this case clear on subLists
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// works anyway, so this implementation is included just for completeness
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// and because subclasses might try to use it.
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protected void removeRange(int fromIndex, int toIndex) {
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subList(fromIndex, toIndex).clear();
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}
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/**
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* Clear the list.
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*/
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public void clear() {
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ends.next = ends.previous = ends;
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modCount++;
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size = 0;
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}
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/**
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* Obtain a ListIterator over this list, starting at a given index. The
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* ListIterator returned by this method supports the add, remove and set
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* methods.
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*
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* @param index the index of the element to be returned by the first call to
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* next(), or size() to be initially positioned at the end of the list.
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* @exception IndexOutOfBoundsException if index < 0 || index > size().
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*/
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public ListIterator listIterator(int index) {
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// Check bounds
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if (index < 0 || index > size) {
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throw new IndexOutOfBoundsException();
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}
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return new Iter(back, getEntry(index, size, ends, ends),
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index, size, modCount);
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}
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/**
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* Obtain a List view of a subsection of this list, from fromIndex
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* (inclusive) to toIndex (exclusive). The returned list is modifiable in
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* every respect. Changes to the returned list are reflected in this list. If
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* this list is structurally modified is any way other than through the
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* returned list, any subsequent operations on the returned list will result
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* in a ConcurrentModificationException (that is, the returned list is
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* fail-fast).
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*
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* @param fromIndex the index that the returned list should start from
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* (inclusive).
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* @param toIndex the index that the returned list should go to (exclusive).
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* @returns a List backed by a subsection of this list.
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* @exception IndexOutOfBoundsException if fromIndex < 0 || toIndex > size()
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* || fromIndex > toIndex.
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*/
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public List subList(int fromIndex, int toIndex) {
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// Check bounds
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if (fromIndex > toIndex || fromIndex < 0 || toIndex > size) {
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throw new IndexOutOfBoundsException();
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}
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return new SubLinkedList(back, modCount,
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getEntry(fromIndex - 1, size, ends, ends),
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getEntry(toIndex, size, ends, ends),
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toIndex - fromIndex);
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}
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private static class SubLinkedList extends AbstractSequentialList {
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Entry head; // entry before the beginning
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Entry tail; // entry after the end
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int size;
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private final Backing b;
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private final Backing back = new Backing() {
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public void checkMod(int known) {
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if (known != modCount) {
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throw new ConcurrentModificationException();
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}
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}
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public void upMod() {
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modCount++;
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}
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public void incSize(int by) {
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size += by;
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}
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public void decSize(int by) {
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size -= by;
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}
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};
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SubLinkedList(Backing backing, int knownMod, Entry h, Entry t, int s) {
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this.modCount = knownMod;
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b = backing;
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head = h;
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tail = t;
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size = s;
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}
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public int size() {
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b.checkMod(this.modCount);
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return size;
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}
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public ListIterator listIterator(int index) {
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b.checkMod(this.modCount);
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// Check bounds
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if (index < 0 || index > size) {
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throw new IndexOutOfBoundsException();
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}
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return new Iter(back, getEntry(index, size, head, tail),
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index, size, modCount);
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}
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public void clear() {
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b.checkMod(this.modCount);
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head.next = tail;
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tail.previous = head;
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size = 0;
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b.decSize(size);
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modCount++;
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b.upMod();
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}
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// No removeRange because this class cannot be publically subclassed.
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public List subList(int fromIndex, int toIndex) {
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b.checkMod(this.modCount);
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// Check bounds
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if (fromIndex > toIndex || fromIndex < 0 || toIndex > size) {
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throw new IndexOutOfBoundsException();
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}
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return new SubLinkedList(back, this.modCount,
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getEntry(fromIndex - 1, size, head, tail),
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getEntry(toIndex, size, head, tail),
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toIndex - fromIndex);
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}
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}
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/**
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* Create a shallow copy of this LinkedList.
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* @return an object of the same class as this object, containing the
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* same elements in the same order.
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*/
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public Object clone()
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{
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LinkedList copy;
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try
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{
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copy = (LinkedList) super.clone();
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}
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catch (CloneNotSupportedException ex)
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{
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throw new InternalError(ex.getMessage());
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}
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copy.size = 0;
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copy.ends = new Entry();
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copy.addAll(this);
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return copy;
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}
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/**
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* Serialize an object to a stream.
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* @serialdata the size of the list (int), followed by all the elements
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* (Object) in proper order.
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*/
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private void writeObject(ObjectOutputStream s)
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throws IOException
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{
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s.writeInt(size);
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for (Iterator i = iterator(); i.hasNext(); )
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s.writeObject(i.next());
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}
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/**
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* Deserialize an object from a stream.
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* @serialdata the size of the list (int), followed by all the elements
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* (Object) in proper order.
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*/
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private void readObject(ObjectInputStream s)
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throws IOException, ClassNotFoundException
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{
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int serialSize = s.readInt();
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ends = new Entry();
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for (int i=0; i< serialSize; i++)
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addLast(s.readObject());
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}
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}
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