--- jsr166/src/main/java/util/LinkedList.java 2003/08/07 15:59:46 1.2 +++ jsr166/src/main/java/util/LinkedList.java 2008/05/18 23:47:56 1.48 @@ -1,74 +1,99 @@ /* - * @(#)LinkedList.java 1.43 01/12/03 + * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * - * Copyright 2002 Sun Microsystems, Inc. All rights reserved. - * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. + * 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. Sun designates this + * particular file as subject to the "Classpath" exception as provided + * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, + * CA 95054 USA or visit www.sun.com if you need additional information or + * have any questions. */ package java.util; /** - * JSR166: Added Queue operations.

* Linked list implementation of the List interface. Implements all * optional list operations, and permits all elements (including * null). In addition to implementing the List interface, * the LinkedList class provides uniformly named methods to * get, remove and insert an element at the * beginning and end of the list. These operations allow linked lists to be - * used as a stack, queue, or double-ended queue (deque).

+ * used as a stack, {@linkplain Queue queue}, or {@linkplain Deque + * double-ended queue}.

* - * All of the stack/queue/deque operations could be easily recast in terms of - * the standard list operations. They're included here primarily for - * convenience, though they may run slightly faster than the equivalent List - * operations.

+ * The class implements the Deque interface, providing + * first-in-first-out queue operations for add, + * poll, along with other stack and deque operations.

* * 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 begining or the end, whichever is closer to the specified index.

+ * the beginning or the end, whichever is closer to the specified index.

* - * Note that this implementation is not synchronized. If multiple - * threads access a list concurrently, and at least one of the threads - * modifies the list structurally, it must 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 - * Collections.synchronizedList method. This is best done at creation time, - * to prevent accidental unsynchronized access to the list: 

- *     List list = Collections.synchronizedList(new LinkedList(...));
- *

+ *

Note that this implementation is not synchronized. + * If multiple threads access a linked list concurrently, and at least + * one of the threads modifies the list structurally, it must 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. * - * The iterators returned by the this class's iterator and + * 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:

+ *   List list = Collections.synchronizedList(new LinkedList(...));
+ * + *

The iterators returned by this class's iterator and * listIterator methods are fail-fast: if the list is - * structurally modified at any time after the iterator is created, in any way - * except through the Iterator's own remove or add methods, - * the iterator will throw a 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. + * structurally modified at any time after the iterator is created, in + * any way except through the Iterator's own remove or + * add 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. * *

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 ConcurrentModificationException on a best-effort basis. + * throw ConcurrentModificationException on a best-effort basis. * Therefore, it would be wrong to write a program that depended on this * exception for its correctness: the fail-fast behavior of iterators * should be used only to detect bugs. * + *

This class is a member of the + * + * Java Collections Framework. + * * @author Josh Bloch - * @version 1.43, 12/03/01 - * @see java.util.List - * @see java.util.ArrayList - * @see java.util.Vector - * @see java.util.Collections#synchronizedList(java.util.List) + * @version %I%, %G% + * @see List + * @see ArrayList + * @see Vector * @since 1.2 + * @param the type of elements held in this collection */ -public class LinkedList extends AbstractSequentialList - implements List, Queue, Cloneable, java.io.Serializable +public class LinkedList + extends AbstractSequentialList + implements List, Deque, Cloneable, java.io.Serializable { - private transient Entry header = new Entry(null, null, null); + private transient Entry header = new Entry(null, null, null); private transient int size = 0; /** @@ -83,21 +108,21 @@ public class LinkedList extends Abstract * 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. + * @param c the collection whose elements are to be placed into this list + * @throws NullPointerException if the specified collection is null */ - public LinkedList(Collection c) { - this(); - addAll(c); - } + public LinkedList(Collection 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. + * @return the first element in this list + * @throws NoSuchElementException if this list is empty */ - public Object getFirst() { + public E getFirst() { if (size==0) throw new NoSuchElementException(); @@ -107,10 +132,10 @@ public class LinkedList extends Abstract /** * Returns the last element in this list. * - * @return the last element in this list. - * @throws NoSuchElementException if this list is empty. + * @return the last element in this list + * @throws NoSuchElementException if this list is empty */ - public Object getLast() { + public E getLast() { if (size==0) throw new NoSuchElementException(); @@ -120,54 +145,51 @@ public class LinkedList extends Abstract /** * Removes and returns the first element from this list. * - * @return the first element from this list. - * @throws NoSuchElementException if this list is empty. + * @return the first element from this list + * @throws NoSuchElementException if this list is empty */ - public Object removeFirst() { - Object first = header.next.element; - remove(header.next); - return first; + 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. + * @return the last element from this list + * @throws NoSuchElementException if this list is empty */ - public Object removeLast() { - Object last = header.previous.element; - remove(header.previous); - return last; + public E removeLast() { + return remove(header.previous); } /** - * Inserts the given element at the beginning of this list. - * - * @param o the element to be inserted at the beginning of this list. + * Inserts the specified element at the beginning of this list. + * + * @param e the element to add */ - public void addFirst(Object o) { - addBefore(o, header.next); + public void addFirst(E e) { + addBefore(e, header.next); } /** - * Appends the given element to the end of this list. (Identical in - * function to the add method; included only for consistency.) - * - * @param o the element to be inserted at the end of this list. + * Appends the specified element to the end of this list. + * + *

This method is equivalent to {@link #add}. + * + * @param e the element to add */ - public void addLast(Object o) { - addBefore(o, header); + public void addLast(E e) { + addBefore(e, header); } /** * Returns true if this list contains the specified element. * More formally, returns true if and only if this list contains - * at least one element e such that (o==null ? e==null - * : o.equals(e)). + * at least one element e such that + * (o==null ? e==null : o.equals(e)). * - * @param o element whose presence in this list is to be tested. - * @return true if this list contains the specified element. + * @param o element whose presence in this list is to be tested + * @return true if this list contains the specified element */ public boolean contains(Object o) { return indexOf(o) != -1; @@ -176,7 +198,7 @@ public class LinkedList extends Abstract /** * Returns the number of elements in this list. * - * @return the number of elements in this list. + * @return the number of elements in this list */ public int size() { return size; @@ -185,35 +207,39 @@ public class LinkedList extends Abstract /** * Appends the specified element to the end of this list. * - * @param o element to be appended to this list. - * @return true (as per the general contract of - * Collection.add). + *

This method is equivalent to {@link #addLast}. + * + * @param e element to be appended to this list + * @return true (as specified by {@link Collection#add}) */ - public boolean add(Object o) { - addBefore(o, header); + public boolean add(E e) { + addBefore(e, header); return true; } /** - * Removes the first occurrence of the specified element in this list. If - * the list does not contain the element, it is unchanged. More formally, - * removes the element with the lowest index i such that - * (o==null ? get(i)==null : o.equals(get(i))) (if such an - * element exists). + * 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 + * i such that + * (o==null ? get(i)==null : o.equals(get(i))) + * (if such an element exists). Returns true 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 true if the list contained the specified element. + * @param o element to be removed from this list, if present + * @return true if this list contained the specified element */ public boolean remove(Object o) { if (o==null) { - for (Entry e = header.next; e != header; e = e.next) { + for (Entry e = header.next; e != header; e = e.next) { if (e.element==null) { remove(e); return true; } } } else { - for (Entry e = header.next; e != header; e = e.next) { + for (Entry e = header.next; e != header; e = e.next) { if (o.equals(e.element)) { remove(e); return true; @@ -228,14 +254,14 @@ public class LinkedList extends Abstract * 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. (This implies that the behavior of this call is undefined if - * the specified Collection is this list, and this list is nonempty.) + * progress. (Note that this will occur if the specified collection is + * this list, and it's nonempty.) * - * @param c the elements to be inserted into this list. - * @return true if this list changed as a result of the call. - * @throws NullPointerException if the specified collection is null. + * @param c collection containing elements to be added to this list + * @return true if this list changed as a result of the call + * @throws NullPointerException if the specified collection is null */ - public boolean addAll(Collection c) { + public boolean addAll(Collection c) { return addAll(size, c); } @@ -247,29 +273,27 @@ public class LinkedList extends Abstract * in the list in the order that they are returned by the * specified collection's iterator. * - * @param index index at which to insert first element - * from the specified collection. - * @param c elements to be inserted into this list. - * @return true if this list changed as a result of the call. - * @throws IndexOutOfBoundsException if the specified index is out of - * range (index < 0 || index > size()). - * @throws NullPointerException if the specified collection is null. - */ - public boolean addAll(int index, Collection c) { - int numNew = c.size(); - if (numNew==0) { - if (index < 0 || index >= size) - throw new IndexOutOfBoundsException(); - else - return false; - } + * @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 true 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 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 successor = (index==size ? header : entry(index)); - Entry predecessor = successor.previous; - Iterator it = c.iterator(); + Entry successor = (index==size ? header : entry(index)); + Entry predecessor = successor.previous; for (int i=0; i e = new Entry((E)a[i], successor, predecessor); predecessor.next = e; predecessor = e; } @@ -283,9 +307,16 @@ public class LinkedList extends Abstract * Removes all of the elements from this list. */ public void clear() { - modCount++; + Entry e = header.next; + while (e != header) { + Entry next = e.next; + e.next = e.previous = null; + e.element = null; + e = next; + } header.next = header.previous = header; size = 0; + modCount++; } @@ -294,13 +325,11 @@ public class LinkedList extends Abstract /** * Returns the element at the specified position in this list. * - * @param index index of element to return. - * @return the element at the specified position in this list. - * - * @throws IndexOutOfBoundsException if the specified index is is out of - * range (index < 0 || index >= size()). + * @param index index of the element to return + * @return the element at the specified position in this list + * @throws IndexOutOfBoundsException {@inheritDoc} */ - public Object get(int index) { + public E get(int index) { return entry(index).element; } @@ -308,15 +337,14 @@ public class LinkedList extends Abstract * Replaces the element at the specified position in this list with the * specified element. * - * @param index index of element to replace. - * @param element element to be stored at the specified position. - * @return the element previously at the specified position. - * @throws IndexOutOfBoundsException if the specified index is out of - * range (index < 0 || index >= size()). - */ - public Object set(int index, Object element) { - Entry e = entry(index); - Object oldVal = e.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 = entry(index); + E oldVal = e.element; e.element = element; return oldVal; } @@ -326,13 +354,11 @@ public class LinkedList extends Abstract * 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 if the specified index is out of - * range (index < 0 || index > size()). + * @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, Object element) { + public void add(int index, E element) { addBefore(element, (index==size ? header : entry(index))); } @@ -341,26 +367,22 @@ public class LinkedList extends Abstract * 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 removed. - * @return the element previously at the specified position. - * - * @throws IndexOutOfBoundsException if the specified index is out of - * range (index < 0 || index >= size()). + * @param index the index of the element to be removed + * @return the element previously at the specified position + * @throws IndexOutOfBoundsException {@inheritDoc} */ - public Object remove(int index) { - Entry e = entry(index); - remove(e); - return e.element; + public E remove(int index) { + return remove(entry(index)); } /** - * Return the indexed entry. + * Returns the indexed entry. */ - private Entry entry(int index) { + private Entry entry(int index) { if (index < 0 || index >= size) throw new IndexOutOfBoundsException("Index: "+index+ ", Size: "+size); - Entry e = header; + Entry e = header; if (index < (size >> 1)) { for (int i = 0; i <= index; i++) e = e.next; @@ -375,16 +397,15 @@ public class LinkedList extends Abstract // Search Operations /** - * Returns the index in this list of the first occurrence of the - * specified element, or -1 if the List does not contain this - * element. More formally, returns the lowest index i such that - * (o==null ? get(i)==null : o.equals(get(i))), or -1 if - * there is no such index. - * - * @param o element to search for. - * @return the index in this list of the first occurrence of the - * specified element, or -1 if the list does not contain this - * element. + * 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 i such that + * (o==null ? get(i)==null : o.equals(get(i))), + * 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; @@ -405,16 +426,15 @@ public class LinkedList extends Abstract } /** - * Returns the index in this list of the last occurrence of the - * specified element, or -1 if the list does not contain this - * element. More formally, returns the highest index i such that - * (o==null ? get(i)==null : o.equals(get(i))), or -1 if - * there is no such index. - * - * @param o element to search for. - * @return the index in this list of the last occurrence of the - * specified element, or -1 if the list does not contain this - * element. + * 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 i such that + * (o==null ? get(i)==null : o.equals(get(i))), + * 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; @@ -434,6 +454,212 @@ public class LinkedList extends Abstract return -1; } + // Queue operations. + + /** + * Retrieves, but does not remove, the head (first element) of this list. + * @return the head of this list, or null 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 null 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 true (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 true (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 true (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 null if this list is empty. + * + * @return the first element of this list, or null + * 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 null if this list is empty. + * + * @return the last element of this list, or null + * 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 null if this list is empty. + * + * @return the first element of this list, or null 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 null if this list is empty. + * + * @return the last element of this list, or null 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. + * + *

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. + * + *

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 true 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 true if the list contained the specified element + * @since 1.6 + */ + public boolean removeLastOccurrence(Object o) { + if (o==null) { + for (Entry e = header.previous; e != header; e = e.previous) { + if (e.element==null) { + remove(e); + return true; + } + } + } else { + for (Entry e = header.previous; e != header; e = e.previous) { + if (o.equals(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. @@ -448,21 +674,20 @@ public class LinkedList extends Abstract * than risking arbitrary, non-deterministic behavior at an undetermined * time in the future. * - * @param index index of first element to be returned from the - * list-iterator (by a call to next). + * @param index index of the first element to be returned from the + * list-iterator (by a call to next) * @return a ListIterator of the elements in this list (in proper - * sequence), starting at the specified position in the list. - * @throws IndexOutOfBoundsException if index is out of range - * (index < 0 || index > size()). - * @see java.util.List#listIterator(int) + * sequence), starting at the specified position in the list + * @throws IndexOutOfBoundsException {@inheritDoc} + * @see List#listIterator(int) */ - public ListIterator listIterator(int index) { + public ListIterator listIterator(int index) { return new ListItr(index); } - private class ListItr implements ListIterator { - private Entry lastReturned = header; - private Entry next; + private class ListItr implements ListIterator { + private Entry lastReturned = header; + private Entry next; private int nextIndex; private int expectedModCount = modCount; @@ -485,7 +710,7 @@ public class LinkedList extends Abstract return nextIndex != size; } - public Object next() { + public E next() { checkForComodification(); if (nextIndex == size) throw new NoSuchElementException(); @@ -500,7 +725,7 @@ public class LinkedList extends Abstract return nextIndex != 0; } - public Object previous() { + public E previous() { if (nextIndex == 0) throw new NoSuchElementException(); @@ -520,30 +745,31 @@ public class LinkedList extends Abstract public void remove() { checkForComodification(); + Entry lastNext = lastReturned.next; try { LinkedList.this.remove(lastReturned); } catch (NoSuchElementException e) { throw new IllegalStateException(); } if (next==lastReturned) - next = lastReturned.next; + next = lastNext; else nextIndex--; lastReturned = header; expectedModCount++; } - public void set(Object o) { + public void set(E e) { if (lastReturned == header) throw new IllegalStateException(); checkForComodification(); - lastReturned.element = o; + lastReturned.element = e; } - public void add(Object o) { + public void add(E e) { checkForComodification(); lastReturned = header; - addBefore(o, next); + addBefore(e, next); nextIndex++; expectedModCount++; } @@ -554,20 +780,20 @@ public class LinkedList extends Abstract } } - private static class Entry { - Object element; - Entry next; - Entry previous; + private static class Entry { + E element; + Entry next; + Entry previous; - Entry(Object element, Entry next, Entry previous) { + Entry(E element, Entry next, Entry previous) { this.element = element; this.next = next; this.previous = previous; } } - private Entry addBefore(Object o, Entry e) { - Entry newEntry = new Entry(o, e, e.previous); + private Entry addBefore(E e, Entry entry) { + Entry newEntry = new Entry(e, entry, entry.previous); newEntry.previous.next = newEntry; newEntry.next.previous = newEntry; size++; @@ -575,38 +801,63 @@ public class LinkedList extends Abstract return newEntry; } - private void remove(Entry e) { + private E remove(Entry 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 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 a shallow copy of this LinkedList. (The elements * themselves are not cloned.) * - * @return a shallow copy of this LinkedList instance. + * @return a shallow copy of this LinkedList instance */ public Object clone() { - LinkedList clone = null; - try { - clone = (LinkedList)super.clone(); - } catch (CloneNotSupportedException e) { + LinkedList clone = null; + try { + clone = (LinkedList) super.clone(); + } catch (CloneNotSupportedException e) { throw new InternalError(); } // Put clone into "virgin" state - clone.header = new Entry(null, null, null); + clone.header = new Entry(null, null, null); clone.header.next = clone.header.previous = clone.header; clone.size = 0; clone.modCount = 0; // Initialize clone with our elements - for (Entry e = header.next; e != header; e = e.next) + for (Entry e = header.next; e != header; e = e.next) clone.add(e.element); return clone; @@ -614,48 +865,72 @@ public class LinkedList extends Abstract /** * Returns an array containing all of the elements in this list - * in the correct order. + * in proper sequence (from first to last element). + * + *

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. + * + *

This method acts as bridge between array-based and collection-based + * APIs. * * @return an array containing all of the elements in this list - * in the correct order. + * in proper sequence */ public Object[] toArray() { Object[] result = new Object[size]; int i = 0; - for (Entry e = header.next; e != header; e = e.next) + for (Entry 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 - * the correct order; 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.

- * - * 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 - * collection is set to null. This is useful in determining the length - * of the list only if the caller knows that the list - * does not contain any null elements. + * 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. + * + *

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 null. + * (This is useful in determining the length of the list only if + * the caller knows that the list does not contain any null elements.) + * + *

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. + * + *

Suppose x is a list known to contain only strings. + * The following code can be used to dump the list into a newly + * allocated array of String: + * + * 

+     *     String[] y = x.toArray(new String[0]);
+ * + * Note that toArray(new Object[0]) is identical in function to + * toArray(). * * @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 a is not a - * supertype of the runtime type of every element in this list. - * @throws NullPointerException if the specified array is null. + * @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 Object[] toArray(Object a[]) { + public T[] toArray(T[] a) { if (a.length < size) - a = (Object[])java.lang.reflect.Array.newInstance( + a = (T[])java.lang.reflect.Array.newInstance( a.getClass().getComponentType(), size); int i = 0; - for (Entry e = header.next; e != header; e = e.next) - a[i++] = e.element; + Object[] result = a; + for (Entry e = header.next; e != header; e = e.next) + result[i++] = e.element; if (a.length > size) a[size] = null; @@ -671,9 +946,9 @@ public class LinkedList extends Abstract * * @serialData The size of the list (the number of elements it * contains) is emitted (int), followed by all of its - * elements (each an Object) in the proper order. + * elements (each an Object) in the proper order. */ - private synchronized void writeObject(java.io.ObjectOutputStream s) + private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { // Write out any hidden serialization magic s.defaultWriteObject(); @@ -690,7 +965,7 @@ public class LinkedList extends Abstract * Reconstitute this LinkedList instance from a stream (that is * deserialize it). */ - private synchronized void readObject(java.io.ObjectInputStream s) + private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in any hidden serialization magic s.defaultReadObject(); @@ -699,36 +974,11 @@ public class LinkedList extends Abstract int size = s.readInt(); // Initialize header - header = new Entry(null, null, null); + header = new Entry(null, null, null); header.next = header.previous = header; // Read in all elements in the proper order. for (int i=0; i