org.xerial.util.ArrayDeque Maven / Gradle / Ivy
/*
* @(#)ArrayDeque.java 1.6 06/04/21
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package org.xerial.util;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;
/**
* Resizable-array implementation of the {@link Deque} interface. Array deques
* have no capacity restrictions; they grow as necessary to support usage. They
* are not thread-safe; in the absence of external synchronization, they do not
* support concurrent access by multiple threads. Null elements are prohibited.
* This class is likely to be faster than {@link Stack} when used as a stack,
* and faster than {@link LinkedList} when used as a queue.
*
*
* Most ArrayDeque operations run in amortized constant time.
* Exceptions include {@link #remove(Object) remove},
* {@link #removeFirstOccurrence removeFirstOccurrence},
* {@link #removeLastOccurrence removeLastOccurrence}, {@link #contains
* contains}, {@link #iterator iterator.remove()}, and the bulk operations, all
* of which run in linear time.
*
*
* The iterators returned by this class's iterator method are
* fail-fast: If the deque is modified at any time after the iterator is
* created, in any way except through the iterator's own remove method,
* the iterator will generally 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. 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 and its iterator implement all of the optional methods of
* the {@link Collection} and {@link Iterator} interfaces.
*
*
* This class is a member of the Java Collections Framework.
*
* @author Josh Bloch and Doug Lea
* @since 1.6
* @param
* the type of elements held in this collection
*/
public class ArrayDeque extends AbstractCollection implements Deque, Cloneable, Serializable
{
/**
* The array in which the elements of the deque are stored. The capacity of
* the deque is the length of this array, which is always a power of two.
* The array is never allowed to become full, except transiently within an
* addX method where it is resized (see doubleCapacity) immediately upon
* becoming full, thus avoiding head and tail wrapping around to equal each
* other. We also guarantee that all array cells not holding deque elements
* are always null.
*/
private transient E[] elements;
/**
* The index of the element at the head of the deque (which is the element
* that would be removed by remove() or pop()); or an arbitrary number equal
* to tail if the deque is empty.
*/
private transient int head;
/**
* The index at which the next element would be added to the tail of the
* deque (via addLast(E), add(E), or push(E)).
*/
private transient int tail;
/**
* The minimum capacity that we'll use for a newly created deque. Must be a
* power of 2.
*/
private static final int MIN_INITIAL_CAPACITY = 8;
// ****** Array allocation and resizing utilities ******
/**
* Allocate empty array to hold the given number of elements.
*
* @param numElements
* the number of elements to hold
*/
private void allocateElements(int numElements)
{
int initialCapacity = MIN_INITIAL_CAPACITY;
// Find the best power of two to hold elements.
// Tests "<=" because arrays aren't kept full.
if (numElements >= initialCapacity)
{
initialCapacity = numElements;
initialCapacity |= (initialCapacity >>> 1);
initialCapacity |= (initialCapacity >>> 2);
initialCapacity |= (initialCapacity >>> 4);
initialCapacity |= (initialCapacity >>> 8);
initialCapacity |= (initialCapacity >>> 16);
initialCapacity++;
if (initialCapacity < 0) // Too many elements, must back off
initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
}
elements = (E[]) new Object[initialCapacity];
}
/**
* Double the capacity of this deque. Call only when full, i.e., when head
* and tail have wrapped around to become equal.
*/
private void doubleCapacity()
{
assert head == tail;
int p = head;
int n = elements.length;
int r = n - p; // number of elements to the right of p
int newCapacity = n << 1;
if (newCapacity < 0)
throw new IllegalStateException("Sorry, deque too big");
Object[] a = new Object[newCapacity];
System.arraycopy(elements, p, a, 0, r);
System.arraycopy(elements, 0, a, r, p);
elements = (E[]) a;
head = 0;
tail = n;
}
/**
* Copies the elements from our element array into the specified array, in
* order (from first to last element in the deque). It is assumed that the
* array is large enough to hold all elements in the deque.
*
* @return its argument
*/
private T[] copyElements(T[] a)
{
if (head < tail)
{
System.arraycopy(elements, head, a, 0, size());
}
else if (head > tail)
{
int headPortionLen = elements.length - head;
System.arraycopy(elements, head, a, 0, headPortionLen);
System.arraycopy(elements, 0, a, headPortionLen, tail);
}
return a;
}
/**
* Constructs an empty array deque with an initial capacity sufficient to
* hold 16 elements.
*/
public ArrayDeque()
{
elements = (E[]) new Object[16];
}
/**
* Constructs an empty array deque with an initial capacity sufficient to
* hold the specified number of elements.
*
* @param numElements
* lower bound on initial capacity of the deque
*/
public ArrayDeque(int numElements)
{
allocateElements(numElements);
}
/**
* Constructs a deque containing the elements of the specified collection,
* in the order they are returned by the collection's iterator. (The first
* element returned by the collection's iterator becomes the first element,
* or front of the deque.)
*
* @param c
* the collection whose elements are to be placed into the deque
* @throws NullPointerException
* if the specified collection is null
*/
public ArrayDeque(Collection< ? extends E> c)
{
allocateElements(c.size());
addAll(c);
}
// The main insertion and extraction methods are addFirst,
// addLast, pollFirst, pollLast. The other methods are defined in
// terms of these.
/**
* Inserts the specified element at the front of this deque.
*
* @param e
* the element to add
* @throws NullPointerException
* if the specified element is null
*/
public void addFirst(E e)
{
if (e == null)
throw new NullPointerException();
elements[head = (head - 1) & (elements.length - 1)] = e;
if (head == tail)
doubleCapacity();
}
/**
* Inserts the specified element at the end of this deque.
*
*
* This method is equivalent to {@link #add}.
*
* @param e
* the element to add
* @throws NullPointerException
* if the specified element is null
*/
public void addLast(E e)
{
if (e == null)
throw new NullPointerException();
elements[tail] = e;
if ((tail = (tail + 1) & (elements.length - 1)) == head)
doubleCapacity();
}
/**
* Inserts the specified element at the front of this deque.
*
* @param e
* the element to add
* @return true (as specified by {@link Deque#offerFirst})
* @throws NullPointerException
* if the specified element is null
*/
public boolean offerFirst(E e)
{
addFirst(e);
return true;
}
/**
* Inserts the specified element at the end of this deque.
*
* @param e
* the element to add
* @return true (as specified by {@link Deque#offerLast})
* @throws NullPointerException
* if the specified element is null
*/
public boolean offerLast(E e)
{
addLast(e);
return true;
}
/**
* @throws NoSuchElementException
* {@inheritDoc}
*/
public E removeFirst()
{
E x = pollFirst();
if (x == null)
throw new NoSuchElementException();
return x;
}
/**
* @throws NoSuchElementException
* {@inheritDoc}
*/
public E removeLast()
{
E x = pollLast();
if (x == null)
throw new NoSuchElementException();
return x;
}
public E pollFirst()
{
int h = head;
E result = elements[h]; // Element is null if deque empty
if (result == null)
return null;
elements[h] = null; // Must null out slot
head = (h + 1) & (elements.length - 1);
return result;
}
public E pollLast()
{
int t = (tail - 1) & (elements.length - 1);
E result = elements[t];
if (result == null)
return null;
elements[t] = null;
tail = t;
return result;
}
/**
* @throws NoSuchElementException
* {@inheritDoc}
*/
public E getFirst()
{
E x = elements[head];
if (x == null)
throw new NoSuchElementException();
return x;
}
/**
* @throws NoSuchElementException
* {@inheritDoc}
*/
public E getLast()
{
E x = elements[(tail - 1) & (elements.length - 1)];
if (x == null)
throw new NoSuchElementException();
return x;
}
public E peekFirst()
{
return elements[head]; // elements[head] is null if deque empty
}
public E peekLast()
{
return elements[(tail - 1) & (elements.length - 1)];
}
/**
* Removes the first occurrence of the specified element in this deque (when
* traversing the deque from head to tail). If the deque does not contain
* the element, it is unchanged. More formally, removes the first element
* e such that o.equals(e) (if such an element exists).
* Returns true if this deque contained the specified element (or
* equivalently, if this deque changed as a result of the call).
*
* @param o
* element to be removed from this deque, if present
* @return true if the deque contained the specified element
*/
public boolean removeFirstOccurrence(Object o)
{
if (o == null)
return false;
int mask = elements.length - 1;
int i = head;
E x;
while ((x = elements[i]) != null)
{
if (o.equals(x))
{
delete(i);
return true;
}
i = (i + 1) & mask;
}
return false;
}
/**
* Removes the last occurrence of the specified element in this deque (when
* traversing the deque from head to tail). If the deque does not contain
* the element, it is unchanged. More formally, removes the last element
* e such that o.equals(e) (if such an element exists).
* Returns true if this deque contained the specified element (or
* equivalently, if this deque changed as a result of the call).
*
* @param o
* element to be removed from this deque, if present
* @return true if the deque contained the specified element
*/
public boolean removeLastOccurrence(Object o)
{
if (o == null)
return false;
int mask = elements.length - 1;
int i = (tail - 1) & mask;
E x;
while ((x = elements[i]) != null)
{
if (o.equals(x))
{
delete(i);
return true;
}
i = (i - 1) & mask;
}
return false;
}
// *** Queue methods ***
/**
* Inserts the specified element at the end of this deque.
*
*
* This method is equivalent to {@link #addLast}.
*
* @param e
* the element to add
* @return true (as specified by {@link Collection#add})
* @throws NullPointerException
* if the specified element is null
*/
public boolean add(E e)
{
addLast(e);
return true;
}
/**
* Inserts the specified element at the end of this deque.
*
*
* This method is equivalent to {@link #offerLast}.
*
* @param e
* the element to add
* @return true (as specified by {@link Queue#offer})
* @throws NullPointerException
* if the specified element is null
*/
public boolean offer(E e)
{
return offerLast(e);
}
/**
* Retrieves and removes the head of the queue represented by this deque.
*
* This method differs from {@link #poll poll} only in that it throws an
* exception if this deque is empty.
*
*
* This method is equivalent to {@link #removeFirst}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException
* {@inheritDoc}
*/
public E remove()
{
return removeFirst();
}
/**
* Retrieves and removes the head of the queue represented by this deque (in
* other words, the first element of this deque), or returns null
* if this deque is empty.
*
*
* This method is equivalent to {@link #pollFirst}.
*
* @return the head of the queue represented by this deque, or null
* if this deque is empty
*/
public E poll()
{
return pollFirst();
}
/**
* Retrieves, but does not remove, the head of the queue represented by this
* deque. This method differs from {@link #peek peek} only in that it throws
* an exception if this deque is empty.
*
*
* This method is equivalent to {@link #getFirst}.
*
* @return the head of the queue represented by this deque
* @throws NoSuchElementException
* {@inheritDoc}
*/
public E element()
{
return getFirst();
}
/**
* Retrieves, but does not remove, the head of the queue represented by this
* deque, or returns null if this deque is empty.
*
*
* This method is equivalent to {@link #peekFirst}.
*
* @return the head of the queue represented by this deque, or null
* if this deque is empty
*/
public E peek()
{
return peekFirst();
}
// *** Stack methods ***
/**
* Pushes an element onto the stack represented by this deque. In other
* words, inserts the element at the front of this deque.
*
*
* This method is equivalent to {@link #addFirst}.
*
* @param e
* the element to push
* @throws NullPointerException
* if the specified element is null
*/
public void push(E e)
{
addFirst(e);
}
/**
* Pops an element from the stack represented by this deque. In other words,
* removes and returns the first element of this deque.
*
*
* This method is equivalent to {@link #removeFirst()}.
*
* @return the element at the front of this deque (which is the top of the
* stack represented by this deque)
* @throws NoSuchElementException
* {@inheritDoc}
*/
public E pop()
{
return removeFirst();
}
private void checkInvariants()
{
assert elements[tail] == null;
assert head == tail ? elements[head] == null : (elements[head] != null && elements[(tail - 1)
& (elements.length - 1)] != null);
assert elements[(head - 1) & (elements.length - 1)] == null;
}
/**
* Removes the element at the specified position in the elements array,
* adjusting head and tail as necessary. This can result in motion of
* elements backwards or forwards in the array.
*
*
* This method is called delete rather than remove to emphasize that its
* semantics differ from those of {@link List#remove(int)}.
*
* @return true if elements moved backwards
*/
private boolean delete(int i)
{
checkInvariants();
final E[] elements = this.elements;
final int mask = elements.length - 1;
final int h = head;
final int t = tail;
final int front = (i - h) & mask;
final int back = (t - i) & mask;
// Invariant: head <= i < tail mod circularity
if (front >= ((t - h) & mask))
throw new ConcurrentModificationException();
// Optimize for least element motion
if (front < back)
{
if (h <= i)
{
System.arraycopy(elements, h, elements, h + 1, front);
}
else
{ // Wrap around
System.arraycopy(elements, 0, elements, 1, i);
elements[0] = elements[mask];
System.arraycopy(elements, h, elements, h + 1, mask - h);
}
elements[h] = null;
head = (h + 1) & mask;
return false;
}
else
{
if (i < t)
{ // Copy the null tail as well
System.arraycopy(elements, i + 1, elements, i, back);
tail = t - 1;
}
else
{ // Wrap around
System.arraycopy(elements, i + 1, elements, i, mask - i);
elements[mask] = elements[0];
System.arraycopy(elements, 1, elements, 0, t);
tail = (t - 1) & mask;
}
return true;
}
}
// *** Collection Methods ***
/**
* Returns the number of elements in this deque.
*
* @return the number of elements in this deque
*/
public int size()
{
return (tail - head) & (elements.length - 1);
}
/**
* Returns true if this deque contains no elements.
*
* @return true if this deque contains no elements
*/
public boolean isEmpty()
{
return head == tail;
}
/**
* Returns an iterator over the elements in this deque. The elements will be
* ordered from first (head) to last (tail). This is the same order that
* elements would be dequeued (via successive calls to {@link #remove} or
* popped (via successive calls to {@link #pop}).
*
* @return an iterator over the elements in this deque
*/
public Iterator iterator()
{
return new DeqIterator();
}
public Iterator descendingIterator()
{
return new DescendingIterator();
}
private class DeqIterator implements Iterator
{
/**
* Index of element to be returned by subsequent call to next.
*/
private int cursor = head;
/**
* Tail recorded at construction (also in remove), to stop iterator and
* also to check for comodification.
*/
private int fence = tail;
/**
* Index of element returned by most recent call to next. Reset to -1 if
* element is deleted by a call to remove.
*/
private int lastRet = -1;
public boolean hasNext()
{
return cursor != fence;
}
public E next()
{
if (cursor == fence)
throw new NoSuchElementException();
E result = elements[cursor];
// This check doesn't catch all possible comodifications,
// but does catch the ones that corrupt traversal
if (tail != fence || result == null)
throw new ConcurrentModificationException();
lastRet = cursor;
cursor = (cursor + 1) & (elements.length - 1);
return result;
}
public void remove()
{
if (lastRet < 0)
throw new IllegalStateException();
if (delete(lastRet))
{ // if left-shifted, undo increment in next()
cursor = (cursor - 1) & (elements.length - 1);
fence = tail;
}
lastRet = -1;
}
}
private class DescendingIterator implements Iterator
{
/*
* This class is nearly a mirror-image of DeqIterator, using
* tail instead of head for initial cursor, and head instead of
* tail for fence.
*/
private int cursor = tail;
private int fence = head;
private int lastRet = -1;
public boolean hasNext()
{
return cursor != fence;
}
public E next()
{
if (cursor == fence)
throw new NoSuchElementException();
cursor = (cursor - 1) & (elements.length - 1);
E result = elements[cursor];
if (head != fence || result == null)
throw new ConcurrentModificationException();
lastRet = cursor;
return result;
}
public void remove()
{
if (lastRet < 0)
throw new IllegalStateException();
if (!delete(lastRet))
{
cursor = (cursor + 1) & (elements.length - 1);
fence = head;
}
lastRet = -1;
}
}
/**
* Returns true if this deque contains the specified element. More
* formally, returns true if and only if this deque contains at
* least one element e such that o.equals(e).
*
* @param o
* object to be checked for containment in this deque
* @return true if this deque contains the specified element
*/
public boolean contains(Object o)
{
if (o == null)
return false;
int mask = elements.length - 1;
int i = head;
E x;
while ((x = elements[i]) != null)
{
if (o.equals(x))
return true;
i = (i + 1) & mask;
}
return false;
}
/**
* Removes a single instance of the specified element from this deque. If
* the deque does not contain the element, it is unchanged. More formally,
* removes the first element e such that o.equals(e) (if
* such an element exists). Returns true if this deque contained
* the specified element (or equivalently, if this deque changed as a result
* of the call).
*
*
* This method is equivalent to {@link #removeFirstOccurrence}.
*
* @param o
* element to be removed from this deque, if present
* @return true if this deque contained the specified element
*/
public boolean remove(Object o)
{
return removeFirstOccurrence(o);
}
/**
* Removes all of the elements from this deque. The deque will be empty
* after this call returns.
*/
public void clear()
{
int h = head;
int t = tail;
if (h != t)
{ // clear all cells
head = tail = 0;
int i = h;
int mask = elements.length - 1;
do
{
elements[i] = null;
i = (i + 1) & mask;
}
while (i != t);
}
}
/**
* Returns an array containing all of the elements in this deque in proper
* sequence (from first to last element).
*
*
* The returned array will be "safe" in that no references to it are
* maintained by this deque. (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 deque
*/
public Object[] toArray()
{
return copyElements(new Object[size()]);
}
/**
* Returns an array containing all of the elements in this deque in proper
* sequence (from first to last element); the runtime type of the returned
* array is that of the specified array. If the deque 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 deque.
*
*
* If this deque fits in the specified array with room to spare (i.e., the
* array has more elements than this deque), the element in the array
* immediately following the end of the deque is set to null.
*
*
* 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 deque known to contain only strings. The
* following code can be used to dump the deque 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 deque 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 all of the elements in this deque
* @throws ArrayStoreException
* if the runtime type of the specified array is not a supertype
* of the runtime type of every element in this deque
* @throws NullPointerException
* if the specified array is null
*/
public T[] toArray(T[] a)
{
int size = size();
if (a.length < size)
a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), size);
copyElements(a);
if (a.length > size)
a[size] = null;
return a;
}
// *** Object methods ***
/**
* Returns a copy of this deque.
*
* @return a copy of this deque
*/
public ArrayDeque clone()
{
try
{
ArrayDeque result = (ArrayDeque) super.clone();
result.elements = copyOf(elements, elements.length);
return result;
}
catch (CloneNotSupportedException e)
{
throw new AssertionError();
}
}
private static T[] copyOf(T[] original, int newLength)
{
return (T[]) copyOf(original, newLength, original.getClass());
}
private static T[] copyOf(U[] original, int newLength, Class< ? extends T[]> newType)
{
T[] copy = ((Object) newType == (Object) Object[].class) ? (T[]) new Object[newLength] : (T[]) Array
.newInstance(newType.getComponentType(), newLength);
System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength));
return copy;
}
/**
* Appease the serialization gods.
*/
private static final long serialVersionUID = 2340985798034038923L;
/**
* Serialize this deque.
*
* @serialData The current size (int) of the deque, followed by all
* of its elements (each an object reference) in first-to-last
* order.
*/
private void writeObject(ObjectOutputStream s) throws IOException
{
s.defaultWriteObject();
// Write out size
s.writeInt(size());
// Write out elements in order.
int mask = elements.length - 1;
for (int i = head; i != tail; i = (i + 1) & mask)
s.writeObject(elements[i]);
}
/**
* Deserialize this deque.
*/
private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException
{
s.defaultReadObject();
// Read in size and allocate array
int size = s.readInt();
allocateElements(size);
head = 0;
tail = size;
// Read in all elements in the proper order.
for (int i = 0; i < size; i++)
elements[i] = (E) s.readObject();
}
}