package java.util;
import com.jopdesign.sys.GC;
import com.jopdesign.sys.Native;
import java.lang.Cloneable;
/*
* %W% %E%
*
* Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
/**
* Linked list implementation of the <tt>List</tt> interface. Implements all
* optional list operations, and permits all elements (including <tt>null</tt>).
* In addition to implementing the <tt>List</tt> interface, the
* <tt>LinkedList</tt> class provides uniformly named methods to <tt>get</tt>,
* <tt>remove</tt> and <tt>insert</tt> an element at the beginning and end of
* the list. These operations allow linked lists to be used as a stack,
* {@linkplain Queue queue}, or {@linkplain Deque double-ended queue}.
* <p>
*
* The class implements the <tt>Deque</tt> interface, providing
* first-in-first-out queue operations for <tt>add</tt>, <tt>poll</tt>, along
* with other stack and deque operations.
* <p>
*
* All of the operations perform as could be expected for a doubly-linked list.
* Operations that index into the list will traverse the list from the beginning
* or the end, whichever is closer to the specified index.
* <p>
*
* <p>
* <strong>Note that this implementation is not synchronized.</strong> If
* multiple threads access a linked list concurrently, and at least one of the
* threads modifies the list structurally, it <i>must</i> be synchronized
* externally. (A structural modification is any operation that adds or deletes
* one or more elements; merely setting the value of an element is not a
* structural modification.) This is typically accomplished by synchronizing on
* some object that naturally encapsulates the list.
*
* If no such object exists, the list should be "wrapped" using the
* {@link Collections#synchronizedList Collections.synchronizedList} method.
* This is best done at creation time, to prevent accidental unsynchronized
* access to the list:
*
* <pre>
* List list = Collections.synchronizedList(new LinkedList(...));
* </pre>
*
* <p>
* The iterators returned by this class's <tt>iterator</tt> and
* <tt>listIterator</tt> methods are <i>fail-fast</i>: if the list is
* structurally modified at any time after the iterator is created, in any way
* except through the Iterator's own <tt>remove</tt> or <tt>add</tt> methods,
* the iterator will throw a {@link ConcurrentModificationException}. Thus, in
* the face of concurrent modification, the iterator fails quickly and cleanly,
* rather than risking arbitrary, non-deterministic behavior at an undetermined
* time in the future.
*
* <p>
* Note that the fail-fast behavior of an iterator cannot be guaranteed as it
* is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators throw
* <tt>ConcurrentModificationException</tt> on a best-effort basis. Therefore,
* it would be wrong to write a program that depended on this exception for its
* correctness: <i>the fail-fast behavior of iterators should be used only to
* detect bugs.</i>
*
* <p>
* This class is a member of the <a href="{@docRoot}
* /../technotes/guides/collections/index.html"> Java Collections Framework</a>.
*
* @author Josh Bloch
* @version %I%, %G%
* @see List
* @see ArrayList
* @see Vector
* @since 1.2
* @param <E>
* the type of elements held in this collection
*/
public class LinkedList<E> extends AbstractSequentialList<E> implements
List<E>, Deque<E> // , Cloneable //, java.io.Serializable
{
private transient Entry<E> header = new Entry<E>(null, null, null);
private transient int size = 0;
/**
* Constructs an empty list.
*/
public LinkedList() {
header.next = header.previous = header;
}
/**
* Constructs a list containing the elements of the specified collection, in
* the order they are returned by the collection's iterator.
*
* @param c
* the collection whose elements are to be placed into this list
* @throws NullPointerException
* if the specified collection is null
*/
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
/**
* Returns the first element in this list.
*
* @return the first element in this list
* @throws NoSuchElementException
* if this list is empty
*/
public E getFirst() {
if (size == 0)
throw new NoSuchElementException();
return header.next.element;
}
/**
* Returns the last element in this list.
*
* @return the last element in this list
* @throws NoSuchElementException
* if this list is empty
*/
public E getLast() {
if (size == 0)
throw new NoSuchElementException();
return header.previous.element;
}
/**
* Removes and returns the first element from this list.
*
* @return the first element from this list
* @throws NoSuchElementException
* if this list is empty
*/
public E removeFirst() {
return remove(header.next);
}
/**
* Removes and returns the last element from this list.
*
* @return the last element from this list
* @throws NoSuchElementException
* if this list is empty
*/
public E removeLast() {
return remove(header.previous);
}
/**
* Inserts the specified element at the beginning of this list.
*
* @param e
* the element to add
*/
public void addFirst(E e) {
addBefore(e, header.next);
}
/**
* Appends the specified element to the end of this list.
*
* <p>
* This method is equivalent to {@link #add}.
*
* @param e
* the element to add
*/
public void addLast(E e) {
addBefore(e, header);
}
/**
* Returns <tt>true</tt> if this list contains the specified element. More
* formally, returns <tt>true</tt> if and only if this list contains at
* least one element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o
* element whose presence in this list is to be tested
* @return <tt>true</tt> if this list contains the specified element
*/
public boolean contains(Object o) {
return indexOf(o) != -1;
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size() {
return size;
}
/**
* Appends the specified element to the end of this list.
*
* <p>
* This method is equivalent to {@link #addLast}.
*
* @param e
* element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
*/
public boolean add(E e) {
addBefore(e, header);
return true;
}
/**
* Removes the first occurrence of the specified element from this list, if
* it is present. If this list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns <tt>true</tt> if this list contained
* the specified element (or equivalently, if this list changed as a result
* of the call).
*
* @param o
* element to be removed from this list, if present
* @return <tt>true</tt> if this list contained the specified element
*/
public boolean remove(Object o) {
if (o == null) {
for (Entry<E> e = header.next; e != header; e = e.next) {
if (e.element == null) {
remove(e);
return true;
}
}
} else {
for (Entry<E> e = header.next; e != header; e = e.next) {
if (o.equals(e.element)) {
remove(e);
return true;
}
}
}
return false;
}
/**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the specified
* collection's iterator. The behavior of this operation is undefined if the
* specified collection is modified while the operation is in progress.
* (Note that this will occur if the specified collection is this list, and
* it's nonempty.)
*
* @param c
* collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws NullPointerException
* if the specified collection is null
*/
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
/**
* Inserts all of the elements in the specified collection into this list,
* starting at the specified position. Shifts the element currently at that
* position (if any) and any subsequent elements to the right (increases
* their indices). The new elements will appear in the list in the order
* that they are returned by the specified collection's iterator.
*
* @param index
* index at which to insert the first element from the specified
* collection
* @param c
* collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws IndexOutOfBoundsException
* {@inheritDoc}
* @throws NullPointerException
* if the specified collection is null
*/
public boolean addAll(int index, Collection<? extends E> c) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: " + index + ", Size: "
+ size);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
modCount++;
Entry<E> successor = (index == size ? header : entry(index));
Entry<E> predecessor = successor.previous;
for (int i = 0; i < numNew; i++) {
Entry<E> e = new Entry<E>((E) a[i], successor, predecessor);
predecessor.next = e;
predecessor = e;
}
successor.previous = predecessor;
size += numNew;
return true;
}
/**
* Removes all of the elements from this list.
*/
public void clear() {
Entry<E> e = header.next;
while (e != header) {
Entry<E> next = e.next;
e.next = e.previous = null;
e.element = null;
e = next;
}
header.next = header.previous = header;
size = 0;
modCount++;
}
// Positional Access Operations
/**
* Returns the element at the specified position in this list.
*
* @param index
* index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public E get(int index) {
return entry(index).element;
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @param index
* index of the element to replace
* @param element
* element to be stored at the specified position
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public E set(int index, E element) {
Entry<E> e = entry(index);
E oldVal = e.element;
e.element = element;
return oldVal;
}
/**
* Inserts the specified element at the specified position in this list.
* Shifts the element currently at that position (if any) and any subsequent
* elements to the right (adds one to their indices).
*
* @param index
* index at which the specified element is to be inserted
* @param element
* element to be inserted
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public void add(int index, E element) {
addBefore(element, (index == size ? header : entry(index)));
}
/**
* Removes the element at the specified position in this list. Shifts any
* subsequent elements to the left (subtracts one from their indices).
* Returns the element that was removed from the list.
*
* @param index
* the index of the element to be removed
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException
* {@inheritDoc}
*/
public E remove(int index) {
return remove(entry(index));
}
/**
* Returns the indexed entry.
*/
private Entry<E> entry(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException("Index: " + index + ", Size: "
+ size);
Entry<E> e = header;
if (index < (size >> 1)) {
for (int i = 0; i <= index; i++)
e = e.next;
} else {
for (int i = size; i > index; i--)
e = e.previous;
}
return e;
}
// Search Operations
/**
* Returns the index of the first occurrence of the specified element in
* this list, or -1 if this list does not contain the element. More
* formally, returns the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o
* element to search for
* @return the index of the first occurrence of the specified element in
* this list, or -1 if this list does not contain the element
*/
public int indexOf(Object o) {
int index = 0;
if (o == null) {
for (Entry e = header.next; e != header; e = e.next) {
if (e.element == null)
return index;
index++;
}
} else {
for (Entry e = header.next; e != header; e = e.next) {
if (o.equals(e.element))
return index;
index++;
}
}
return -1;
}
/**
* Returns the index of the last occurrence of the specified element in this
* list, or -1 if this list does not contain the element. More formally,
* returns the highest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o
* element to search for
* @return the index of the last occurrence of the specified element in this
* list, or -1 if this list does not contain the element
*/
public int lastIndexOf(Object o) {
int index = size;
if (o == null) {
for (Entry e = header.previous; e != header; e = e.previous) {
index--;
if (e.element == null)
return index;
}
} else {
for (Entry e = header.previous; e != header; e = e.previous) {
index--;
if (o.equals(e.element))
return index;
}
}
return -1;
}
// Queue operations.
/**
* Retrieves, but does not remove, the head (first element) of this list.
*
* @return the head of this list, or <tt>null</tt> if this list is empty
* @since 1.5
*/
public E peek() {
if (size == 0)
return null;
return getFirst();
}
/**
* Retrieves, but does not remove, the head (first element) of this list.
*
* @return the head of this list
* @throws NoSuchElementException
* if this list is empty
* @since 1.5
*/
public E element() {
return getFirst();
}
/**
* Retrieves and removes the head (first element) of this list
*
* @return the head of this list, or <tt>null</tt> if this list is empty
* @since 1.5
*/
public E poll() {
if (size == 0)
return null;
return removeFirst();
}
/**
* Retrieves and removes the head (first element) of this list.
*
* @return the head of this list
* @throws NoSuchElementException
* if this list is empty
* @since 1.5
*/
public E remove() {
return removeFirst();
}
/**
* Adds the specified element as the tail (last element) of this list.
*
* @param e
* the element to add
* @return <tt>true</tt> (as specified by {@link Queue#offer})
* @since 1.5
*/
public boolean offer(E e) {
return add(e);
}
// Deque operations
/**
* Inserts the specified element at the front of this list.
*
* @param e
* the element to insert
* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
* @since 1.6
*/
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
/**
* Inserts the specified element at the end of this list.
*
* @param e
* the element to insert
* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
* @since 1.6
*/
public boolean offerLast(E e) {
addLast(e);
return true;
}
/**
* Retrieves, but does not remove, the first element of this list, or
* returns <tt>null</tt> if this list is empty.
*
* @return the first element of this list, or <tt>null</tt> if this list is
* empty
* @since 1.6
*/
public E peekFirst() {
if (size == 0)
return null;
return getFirst();
}
/**
* Retrieves, but does not remove, the last element of this list, or returns
* <tt>null</tt> if this list is empty.
*
* @return the last element of this list, or <tt>null</tt> if this list is
* empty
* @since 1.6
*/
public E peekLast() {
if (size == 0)
return null;
return getLast();
}
/**
* Retrieves and removes the first element of this list, or returns
* <tt>null</tt> if this list is empty.
*
* @return the first element of this list, or <tt>null</tt> if this list is
* empty
* @since 1.6
*/
public E pollFirst() {
if (size == 0)
return null;
return removeFirst();
}
/**
* Retrieves and removes the last element of this list, or returns
* <tt>null</tt> if this list is empty.
*
* @return the last element of this list, or <tt>null</tt> if this list is
* empty
* @since 1.6
*/
public E pollLast() {
if (size == 0)
return null;
return removeLast();
}
/**
* Pushes an element onto the stack represented by this list. In other
* words, inserts the element at the front of this list.
*
* <p>
* This method is equivalent to {@link #addFirst}.
*
* @param e
* the element to push
* @since 1.6
*/
public void push(E e) {
addFirst(e);
}
/**
* Pops an element from the stack represented by this list. In other words,
* removes and returns the first element of this list.
*
* <p>
* This method is equivalent to {@link #removeFirst()}.
*
* @return the element at the front of this list (which is the top of the
* stack represented by this list)
* @throws NoSuchElementException
* if this list is empty
* @since 1.6
*/
public E pop() {
return removeFirst();
}
/**
* Removes the first occurrence of the specified element in this list (when
* traversing the list from head to tail). If the list does not contain the
* element, it is unchanged.
*
* @param o
* element to be removed from this list, if present
* @return <tt>true</tt> if the list contained the specified element
* @since 1.6
*/
public boolean removeFirstOccurrence(Object o) {
return remove(o);
}
/**
* Removes the last occurrence of the specified element in this list (when
* traversing the list from head to tail). If the list does not contain the
* element, it is unchanged.
*
* @param o
* element to be removed from this list, if present
* @return <tt>true</tt> if the list contained the specified element
* @since 1.6
*/
public boolean removeLastOccurrence(Object o) {
if (o == null) {
for (Entry<E> e = header.previous; e != header; e = e.previous) {
if (e.element == null) {
remove(e);
return true;
}
}
} else {
for (Entry<E> 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. Obeys the
* general contract of <tt>List.listIterator(int)</tt>.
* <p>
*
* The list-iterator is <i>fail-fast</i>: if the list is structurally
* modified at any time after the Iterator is created, in any way except
* through the list-iterator's own <tt>remove</tt> or <tt>add</tt> methods,
* the list-iterator will throw a <tt>ConcurrentModificationException</tt>.
* Thus, in the face of concurrent modification, the iterator fails quickly
* and cleanly, rather than risking arbitrary, non-deterministic behavior at
* an undetermined time in the future.
*
* @param index
* index of the first element to be returned from the
* list-iterator (by a call to <tt>next</tt>)
* @return a ListIterator of the elements in this list (in proper sequence),
* starting at the specified position in the list
* @throws IndexOutOfBoundsException
* {@inheritDoc}
* @see List#listIterator(int)
*/
public ListIterator<E> listIterator(int index) {
return new ListItr(index);
}
private class ListItr implements ListIterator<E> {
private Entry<E> lastReturned = header;
private Entry<E> next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: " + index
+ ", Size: " + size);
if (index < (size >> 1)) {
next = header.next;
for (nextIndex = 0; nextIndex < index; nextIndex++)
next = next.next;
} else {
next = header;
for (nextIndex = size; nextIndex > index; nextIndex--)
next = next.previous;
}
}
public boolean hasNext() {
return nextIndex != size;
}
public E next() {
checkForComodification();
if (nextIndex == size)
throw new NoSuchElementException();
lastReturned = next;
next = next.next;
nextIndex++;
return lastReturned.element;
}
public boolean hasPrevious() {
return nextIndex != 0;
}
public E previous() {
if (nextIndex == 0)
throw new NoSuchElementException();
lastReturned = next = next.previous;
nextIndex--;
checkForComodification();
return lastReturned.element;
}
public int nextIndex() {
return nextIndex;
}
public int previousIndex() {
return nextIndex - 1;
}
public void remove() {
checkForComodification();
Entry<E> lastNext = lastReturned.next;
try {
LinkedList.this.remove(lastReturned);
} catch (NoSuchElementException e) {
throw new IllegalStateException();
}
if (next == lastReturned)
next = lastNext;
else
nextIndex--;
lastReturned = header;
expectedModCount++;
}
public void set(E e) {
if (lastReturned == header)
throw new IllegalStateException();
checkForComodification();
lastReturned.element = e;
}
public void add(E e) {
checkForComodification();
lastReturned = header;
addBefore(e, next);
nextIndex++;
expectedModCount++;
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
private static class Entry<E> {
E element;
Entry<E> next;
Entry<E> previous;
Entry(E element, Entry<E> next, Entry<E> previous) {
this.element = element;
this.next = next;
this.previous = previous;
}
}
private Entry<E> addBefore(E e, Entry<E> entry) {
Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);
newEntry.previous.next = newEntry;
newEntry.next.previous = newEntry;
size++;
modCount++;
return newEntry;
}
private E remove(Entry<E> e) {
if (e == header)
throw new NoSuchElementException();
E result = e.element;
e.previous.next = e.next;
e.next.previous = e.previous;
e.next = e.previous = null;
e.element = null;
size--;
modCount++;
return result;
}
/**
* @since 1.6
*/
public Iterator<E> descendingIterator() {
return new DescendingIterator();
}
/** Adapter to provide descending iterators via ListItr.previous */
private class DescendingIterator implements Iterator {
final ListItr itr = new ListItr(size());
public boolean hasNext() {
return itr.hasPrevious();
}
public E next() {
return itr.previous();
}
public void remove() {
itr.remove();
}
}
/**
* Returns a shallow copy of this <tt>LinkedList</tt>. (The elements
* themselves are not cloned.)
*
* @return a shallow copy of this <tt>LinkedList</tt> instance
*/
// public Object clone() {
// LinkedList<E> clone = null;
// try {
// clone = (LinkedList<E>) super.clone();
// } catch (CloneNotSupportedException e) {
// throw new InternalError();
// }
//
// // Put clone into "virgin" state
// clone.header = new Entry<E>(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> e = header.next; e != header; e = e.next)
// clone.add(e.element);
//
// return clone;
// }
/**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element).
*
* <p>
* The returned array will be "safe" in that no references to it are
* maintained by this list. (In other words, this method must allocate a new
* array). The caller is thus free to modify the returned array.
*
* <p>
* This method acts as bridge between array-based and collection-based APIs.
*
* @return an array containing all of the elements in this list in proper
* sequence
*/
public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (Entry<E> e = header.next; e != header; e = e.next)
result[i++] = e.element;
return result;
}
/**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element); the runtime type of the returned
* array is that of the specified array. If the list fits in the specified
* array, it is returned therein. Otherwise, a new array is allocated with
* the runtime type of the specified array and the size of this list.
*
* <p>
* If the list fits in the specified array with room to spare (i.e., the
* array has more elements than the list), the element in the array
* immediately following the end of the list is set to <tt>null</tt>. (This
* is useful in determining the length of the list <i>only</i> if the caller
* knows that the list does not contain any null elements.)
*
* <p>
* Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may, under
* certain circumstances, be used to save allocation costs.
*
* <p>
* Suppose <tt>x</tt> is a list known to contain only strings. The following
* code can be used to dump the list into a newly allocated array of
* <tt>String</tt>:
*
* <pre>
* String[] y = x.toArray(new String[0]);
* </pre>
*
* Note that <tt>toArray(new Object[0])</tt> is identical in function to
* <tt>toArray()</tt>.
*
* @param a
* the array into which the elements of the list are to be
* stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the list
* @throws ArrayStoreException
* if the runtime type of the specified array is not a supertype
* of the runtime type of every element in this list
* @throws NullPointerException
* if the specified array is null
*/
public <T> T[] toArray(T[] a) {
if (a.length < size) {
int arrRef = Native.toInt(a);
int arrType = Native.rdMem(arrRef + GC.OFF_TYPE);
// Does this works??
a = (T[]) Native.toObject(GC.newArray(size, arrType));
// a = (T[]) java.lang.reflect.Array.newInstance(a.getClass()
// .getComponentType(), size);
}
int i = 0;
Object[] result = a;
for (Entry<E> e = header.next; e != header; e = e.next)
result[i++] = e.element;
if (a.length > size)
a[size] = null;
return a;
}
// private static final long serialVersionUID = 876323262645176354L;
/**
* Save the state of this <tt>LinkedList</tt> instance to a stream (that 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.
*/
// private void writeObject(java.io.ObjectOutputStream s)
// throws java.io.IOException {
// // Write out any hidden serialization magic
// s.defaultWriteObject();
//
// // Write out size
// s.writeInt(size);
//
// // Write out all elements in the proper order.
// for (Entry e = header.next; e != header; e = e.next)
// s.writeObject(e.element);
// }
/**
* Reconstitute this <tt>LinkedList</tt> instance from a stream (that is
* deserialize it).
*/
// private void readObject(java.io.ObjectInputStream s)
// throws java.io.IOException, ClassNotFoundException {
// // Read in any hidden serialization magic
// s.defaultReadObject();
//
// // Read in size
// int size = s.readInt();
//
// // Initialize header
// header = new Entry<E>(null, null, null);
// header.next = header.previous = header;
//
// // Read in all elements in the proper order.
// for (int i=0; i<size; i++)
// addBefore((E)s.readObject(), header);
// }
}