--- jsr166/src/main/java/util/LinkedList.java 2003/09/12 15:38:26 1.7 +++ jsr166/src/main/java/util/LinkedList.java 2006/01/10 21:32:09 1.43 @@ -1,11 +1,12 @@ /* * %W% %E% * - * Copyright 2003 Sun Microsystems, Inc. All rights reserved. + * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util; +import java.util.*; // for javadoc (till 6280605 is fixed) /** * Linked list implementation of the List interface. Implements all @@ -14,40 +15,41 @@ package java.util; * 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}.

* - * The class implements the Queue interface, providing + * The class implements the Deque interface, providing * first-in-first-out queue operations for add, - * poll, etc. Other stack and 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.

+ * 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 @@ -55,9 +57,9 @@ package java.util; * 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.

+ * should be used only to detect bugs. * - * This class is a member of the + *

This class is a member of the * * Java Collections Framework. * @@ -66,13 +68,13 @@ package java.util; * @see List * @see ArrayList * @see Vector - * @see Collections#synchronizedList(List) * @since 1.2 + * @param the type of elements held in this collection */ public class LinkedList extends AbstractSequentialList - implements List, Queue, Cloneable, java.io.Serializable + implements List, Deque, Cloneable, java.io.Serializable { private transient Entry header = new Entry(null, null, null); private transient int size = 0; @@ -89,19 +91,19 @@ public class LinkedList * 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 E getFirst() { if (size==0) @@ -113,8 +115,8 @@ public class LinkedList /** * 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 E getLast() { if (size==0) @@ -126,54 +128,51 @@ public class LinkedList /** * 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 E removeFirst() { - E first = header.next.element; - remove(header.next); - return first; + 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 E removeLast() { - E last = header.previous.element; - remove(header.previous); - return last; + return remove(header.previous); } /** - * Inserts the given element at the beginning of this list. + * Inserts the specified element at the beginning of this list. * - * @param o the element to be inserted at the beginning of this list. + * @param e the element to add */ - public void addFirst(E 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.) + * Appends the specified element to the end of this list. + * + *

This method is equivalent to {@link #add}. * - * @param o the element to be inserted at the end of this list. + * @param e the element to add */ - public void addLast(E 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; @@ -182,7 +181,7 @@ public class LinkedList /** * 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; @@ -191,24 +190,28 @@ public class LinkedList /** * 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(E 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) { @@ -234,12 +237,12 @@ public class LinkedList * 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) { return addAll(size, c); @@ -253,13 +256,12 @@ public class LinkedList * 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. + * @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) @@ -288,9 +290,16 @@ public class LinkedList * 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; + size = 0; + modCount++; } @@ -299,11 +308,9 @@ public class LinkedList /** * 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 E get(int index) { return entry(index).element; @@ -313,11 +320,10 @@ public class LinkedList * 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()). + * @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); @@ -331,11 +337,9 @@ public class LinkedList * 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, E element) { addBefore(element, (index==size ? header : entry(index))); @@ -346,20 +350,16 @@ public class LinkedList * 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 E remove(int index) { - Entry e = entry(index); - remove(e); - return e.element; + return remove(entry(index)); } /** - * Return the indexed entry. + * Returns the indexed entry. */ private Entry entry(int index) { if (index < 0 || index >= size) @@ -380,16 +380,15 @@ public class LinkedList // 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; @@ -410,16 +409,15 @@ public class LinkedList } /** - * 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; @@ -443,7 +441,7 @@ public class LinkedList /** * Retrieves, but does not remove, the head (first element) of this list. - * @return the head of this queue, or null if this queue is empty. + * @return the head of this list, or null if this list is empty * @since 1.5 */ public E peek() { @@ -454,8 +452,8 @@ public class LinkedList /** * Retrieves, but does not remove, the head (first element) of this list. - * @return the head of this queue. - * @throws NoSuchElementException if this queue is empty. + * @return the head of this list + * @throws NoSuchElementException if this list is empty * @since 1.5 */ public E element() { @@ -463,8 +461,8 @@ public class LinkedList } /** - * Retrieves and removes the head (first element) of this list. - * @return the head of this queue, or null if this queue is empty. + * 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() { @@ -475,8 +473,9 @@ public class LinkedList /** * Retrieves and removes the head (first element) of this list. - * @return the head of this queue. - * @throws NoSuchElementException if this queue is empty. + * + * @return the head of this list + * @throws NoSuchElementException if this list is empty * @since 1.5 */ public E remove() { @@ -486,13 +485,162 @@ public class LinkedList /** * Adds the specified element as the tail (last element) of this list. * - * @param x the element to add. - * @return true (as per the general contract of - * Queue.offer) + * @param e the element to add + * @return true (as specified by {@link Queue#offer}) * @since 1.5 */ - public boolean offer(E x) { - return add(x); + 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; } /** @@ -509,12 +657,11 @@ public class LinkedList * 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()). + * sequence), starting at the specified position in the list + * @throws IndexOutOfBoundsException {@inheritDoc} * @see List#listIterator(int) */ public ListIterator listIterator(int index) { @@ -581,30 +728,31 @@ public class LinkedList 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(E o) { + public void set(E e) { if (lastReturned == header) throw new IllegalStateException(); checkForComodification(); - lastReturned.element = o; + lastReturned.element = e; } - public void add(E o) { + public void add(E e) { checkForComodification(); lastReturned = header; - addBefore(o, next); + addBefore(e, next); nextIndex++; expectedModCount++; } @@ -627,8 +775,8 @@ public class LinkedList } } - private Entry addBefore(E 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++; @@ -636,21 +784,46 @@ public class LinkedList 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; @@ -675,10 +848,17 @@ public class LinkedList /** * 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]; @@ -690,25 +870,41 @@ public class LinkedList /** * 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. + * 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[] toArray(T[] a) { if (a.length < size) @@ -732,8 +928,8 @@ public class LinkedList * is, serialize it). * * @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. + * contains) is emitted (int), followed by all of its + * elements (each an Object) in the proper order. */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {