--- jsr166/src/main/java/util/ArrayDeque.java 2005/05/17 16:14:34 1.12 +++ jsr166/src/main/java/util/ArrayDeque.java 2013/02/01 01:02:25 1.45 @@ -1,10 +1,14 @@ /* - * Written by Josh Bloch of Google Inc. and released to the public domain, - * as explained at http://creativecommons.org/licenses/publicdomain. + * Written by Doug Lea with assistance from members of JCP JSR-166 + * Expert Group and released to the public domain, as explained at + * http://creativecommons.org/publicdomain/zero/1.0/ */ package java.util; -import java.io.*; +import java.util.Spliterator; +import java.util.stream.Stream; +import java.util.stream.Streams; +import java.util.function.Consumer; /** * Resizable-array implementation of the {@link Deque} interface. Array @@ -15,16 +19,16 @@ import java.io.*; * {@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. + *

Most {@code 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 + *

The iterators returned by this class's {@code 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 + * is created, in any way except through the iterator's own {@code 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 @@ -34,7 +38,7 @@ import java.io.*; *

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 {@code 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. @@ -44,7 +48,7 @@ import java.io.*; * Iterator} interfaces. * *

This class is a member of the - * + * * Java Collections Framework. * * @author Josh Bloch and Doug Lea @@ -52,7 +56,7 @@ import java.io.*; * @param the type of elements held in this collection */ public class ArrayDeque extends AbstractCollection - implements Deque, Cloneable, Serializable + implements Deque, Cloneable, java.io.Serializable { /** * The array in which the elements of the deque are stored. @@ -64,20 +68,20 @@ public class ArrayDeque extends Abstr * other. We also guarantee that all array cells not holding * deque elements are always null. */ - private transient E[] elements; + transient Object[] elements; // non-private to simplify nested class access /** * 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; + 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; + transient int tail; /** * The minimum capacity that we'll use for a newly created deque. @@ -88,7 +92,7 @@ public class ArrayDeque extends Abstr // ****** Array allocation and resizing utilities ****** /** - * Allocate empty array to hold the given number of elements. + * Allocates empty array to hold the given number of elements. * * @param numElements the number of elements to hold */ @@ -108,11 +112,11 @@ public class ArrayDeque extends Abstr if (initialCapacity < 0) // Too many elements, must back off initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements } - elements = (E[]) new Object[initialCapacity]; + elements = new Object[initialCapacity]; } /** - * Double the capacity of this deque. Call only when full, i.e., + * Doubles the capacity of this deque. Call only when full, i.e., * when head and tail have wrapped around to become equal. */ private void doubleCapacity() { @@ -126,7 +130,7 @@ public class ArrayDeque extends Abstr Object[] a = new Object[newCapacity]; System.arraycopy(elements, p, a, 0, r); System.arraycopy(elements, 0, a, r, p); - elements = (E[])a; + elements = a; head = 0; tail = n; } @@ -154,7 +158,7 @@ public class ArrayDeque extends Abstr * sufficient to hold 16 elements. */ public ArrayDeque() { - elements = (E[]) new Object[16]; + elements = new Object[16]; } /** @@ -202,7 +206,8 @@ public class ArrayDeque extends Abstr /** * Inserts the specified element at the end of this deque. - * This method is equivalent to {@link #add} and {@link #push}. + * + *

This method is equivalent to {@link #add}. * * @param e the element to add * @throws NullPointerException if the specified element is null @@ -219,7 +224,7 @@ public class ArrayDeque extends Abstr * Inserts the specified element at the front of this deque. * * @param e the element to add - * @return true (as per the spec for {@link Deque#offerFirst}) + * @return {@code true} (as specified by {@link Deque#offerFirst}) * @throws NullPointerException if the specified element is null */ public boolean offerFirst(E e) { @@ -231,7 +236,7 @@ public class ArrayDeque extends Abstr * Inserts the specified element at the end of this deque. * * @param e the element to add - * @return true (as per the spec for {@link Deque#offerLast}) + * @return {@code true} (as specified by {@link Deque#offerLast}) * @throws NullPointerException if the specified element is null */ public boolean offerLast(E e) { @@ -261,7 +266,9 @@ public class ArrayDeque extends Abstr public E pollFirst() { int h = head; - E result = elements[h]; // Element is null if deque empty + @SuppressWarnings("unchecked") + E result = (E) elements[h]; + // Element is null if deque empty if (result == null) return null; elements[h] = null; // Must null out slot @@ -271,7 +278,8 @@ public class ArrayDeque extends Abstr public E pollLast() { int t = (tail - 1) & (elements.length - 1); - E result = elements[t]; + @SuppressWarnings("unchecked") + E result = (E) elements[t]; if (result == null) return null; elements[t] = null; @@ -283,48 +291,53 @@ public class ArrayDeque extends Abstr * @throws NoSuchElementException {@inheritDoc} */ public E getFirst() { - E x = elements[head]; - if (x == null) + @SuppressWarnings("unchecked") + E result = (E) elements[head]; + if (result == null) throw new NoSuchElementException(); - return x; + return result; } /** * @throws NoSuchElementException {@inheritDoc} */ public E getLast() { - E x = elements[(tail - 1) & (elements.length - 1)]; - if (x == null) + @SuppressWarnings("unchecked") + E result = (E) elements[(tail - 1) & (elements.length - 1)]; + if (result == null) throw new NoSuchElementException(); - return x; + return result; } + @SuppressWarnings("unchecked") public E peekFirst() { - return elements[head]; // elements[head] is null if deque empty + // elements[head] is null if deque empty + return (E) elements[head]; } + @SuppressWarnings("unchecked") public E peekLast() { - return elements[(tail - 1) & (elements.length - 1)]; + return (E) 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 + * More formally, removes the first element {@code e} such that + * {@code o.equals(e)} (if such an element exists). + * Returns {@code 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 + * @return {@code 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; + Object x; while ( (x = elements[i]) != null) { if (o.equals(x)) { delete(i); @@ -339,20 +352,20 @@ public class ArrayDeque extends Abstr * 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 + * More formally, removes the last element {@code e} such that + * {@code o.equals(e)} (if such an element exists). + * Returns {@code 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 + * @return {@code 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; + Object x; while ( (x = elements[i]) != null) { if (o.equals(x)) { delete(i); @@ -371,7 +384,7 @@ public class ArrayDeque extends Abstr *

This method is equivalent to {@link #addLast}. * * @param e the element to add - * @return true (as per the spec for {@link Collection#add}) + * @return {@code true} (as specified by {@link Collection#add}) * @throws NullPointerException if the specified element is null */ public boolean add(E e) { @@ -385,7 +398,7 @@ public class ArrayDeque extends Abstr *

This method is equivalent to {@link #offerLast}. * * @param e the element to add - * @return true (as per the spec for {@link Queue#offer}) + * @return {@code true} (as specified by {@link Queue#offer}) * @throws NullPointerException if the specified element is null */ public boolean offer(E e) { @@ -394,7 +407,8 @@ public class ArrayDeque extends Abstr /** * Retrieves and removes the head of the queue represented by this deque. - * This method differs from {@link #poll} only in that it throws an + * + * 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}. @@ -409,12 +423,12 @@ public class ArrayDeque extends Abstr /** * 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. + * {@code 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 + * {@code null} if this deque is empty */ public E poll() { return pollFirst(); @@ -422,8 +436,8 @@ public class ArrayDeque extends Abstr /** * Retrieves, but does not remove, the head of the queue represented by - * this deque. This method differs from {@link #peek} only in that it - * throws an exception if this deque is empty. + * 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}. * @@ -436,12 +450,12 @@ public class ArrayDeque extends Abstr /** * Retrieves, but does not remove, the head of the queue represented by - * this deque, or returns null if this deque is empty. + * this deque, or returns {@code 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 + * {@code null} if this deque is empty */ public E peek() { return peekFirst(); @@ -476,6 +490,14 @@ public class ArrayDeque extends Abstr 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 @@ -487,26 +509,42 @@ public class ArrayDeque extends Abstr * @return true if elements moved backwards */ private boolean delete(int i) { - int mask = elements.length - 1; - - // Invariant: head <= i < tail mod circularity - if (((i - head) & mask) >= ((tail - head) & mask)) - throw new ConcurrentModificationException(); - - // Case 1: Deque doesn't wrap - // Case 2: Deque does wrap and removed element is in the head portion - if (i >= head) { - System.arraycopy(elements, head, elements, head + 1, i - head); - elements[head] = null; - head = (head + 1) & mask; + checkInvariants(); + final Object[] 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; } - - // Case 3: Deque wraps and removed element is in the tail portion - tail--; - System.arraycopy(elements, i + 1, elements, i, tail - i); - elements[tail] = null; - return true; } // *** Collection Methods *** @@ -521,9 +559,9 @@ public class ArrayDeque extends Abstr } /** - * Returns true if this deque contains no elements. + * Returns {@code true} if this deque contains no elements. * - * @return true if this deque contains no elements + * @return {@code true} if this deque contains no elements */ public boolean isEmpty() { return head == tail; @@ -535,12 +573,16 @@ public class ArrayDeque extends Abstr * 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 + * @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. @@ -564,12 +606,13 @@ public class ArrayDeque extends Abstr } public E next() { - E result; if (cursor == fence) throw new NoSuchElementException(); + @SuppressWarnings("unchecked") + E result = (E) elements[cursor]; // This check doesn't catch all possible comodifications, // but does catch the ones that corrupt traversal - if (tail != fence || (result = elements[cursor]) == null) + if (tail != fence || result == null) throw new ConcurrentModificationException(); lastRet = cursor; cursor = (cursor + 1) & (elements.length - 1); @@ -579,27 +622,65 @@ public class ArrayDeque extends Abstr public void remove() { if (lastRet < 0) throw new IllegalStateException(); - if (delete(lastRet)) - cursor--; + 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); + @SuppressWarnings("unchecked") + E result = (E) 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; - fence = tail; } } /** - * 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). + * Returns {@code true} if this deque contains the specified element. + * More formally, returns {@code true} if and only if this deque contains + * at least one element {@code e} such that {@code o.equals(e)}. * * @param o object to be checked for containment in this deque - * @return true if this deque contains the specified element + * @return {@code 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; + Object x; while ( (x = elements[i]) != null) { if (o.equals(x)) return true; @@ -611,15 +692,15 @@ public class ArrayDeque extends Abstr /** * 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 + * More formally, removes the first element {@code e} such that + * {@code o.equals(e)} (if such an element exists). + * Returns {@code 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 + * @return {@code true} if this deque contained the specified element */ public boolean remove(Object o) { return removeFirstOccurrence(o); @@ -650,14 +731,14 @@ public class ArrayDeque extends Abstr *

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()]); + return copyElements(new Object[size()]); } /** @@ -671,22 +752,21 @@ public class ArrayDeque extends Abstr *

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. + * {@code 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. + *

Suppose {@code 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: + * allocated array of {@code String}: * - * 

-     *     String[] y = x.toArray(new String[0]);
+ * 
 {@code String[] y = x.toArray(new String[0]);}
* - * Note that toArray(new Object[0]) is identical in function to - * toArray(). + * Note that {@code toArray(new Object[0])} is identical in function to + * {@code 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 @@ -697,12 +777,13 @@ public class ArrayDeque extends Abstr * this deque * @throws NullPointerException if the specified array is null */ + @SuppressWarnings("unchecked") 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); + copyElements(a); if (a.length > size) a[size] = null; return a; @@ -717,50 +798,42 @@ public class ArrayDeque extends Abstr */ public ArrayDeque clone() { try { + @SuppressWarnings("unchecked") ArrayDeque result = (ArrayDeque) super.clone(); - // These two lines are currently faster than cloning the array: - result.elements = (E[]) new Object[elements.length]; - System.arraycopy(elements, 0, result.elements, 0, elements.length); + result.elements = Arrays.copyOf(elements, elements.length); return result; - } catch (CloneNotSupportedException e) { throw new AssertionError(); } } - /** - * Appease the serialization gods. - */ private static final long serialVersionUID = 2340985798034038923L; /** - * Serialize this deque. + * Saves this deque to a stream (that is, serializes it). * - * @serialData The current size (int) of the deque, + * @serialData The current size ({@code 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 { + private void writeObject(java.io.ObjectOutputStream s) + throws java.io.IOException { s.defaultWriteObject(); // Write out size - int size = size(); - s.writeInt(size); + s.writeInt(size()); // Write out elements in order. - int i = head; int mask = elements.length - 1; - for (int j = 0; j < size; j++) { + for (int i = head; i != tail; i = (i + 1) & mask) s.writeObject(elements[i]); - i = (i + 1) & mask; - } } /** - * Deserialize this deque. + * Reconstitutes this deque from a stream (that is, deserializes it). */ - private void readObject(ObjectInputStream s) - throws IOException, ClassNotFoundException { + private void readObject(java.io.ObjectInputStream s) + throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); // Read in size and allocate array @@ -771,7 +844,83 @@ public class ArrayDeque extends Abstr // Read in all elements in the proper order. for (int i = 0; i < size; i++) - elements[i] = (E)s.readObject(); + elements[i] = s.readObject(); + } + + public Stream stream() { + int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED; + return Streams.stream + (() -> new DeqSpliterator(this, head, tail), flags); + } + public Stream parallelStream() { + int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED; + return Streams.parallelStream + (() -> new DeqSpliterator(this, head, tail), flags); + } + + static final class DeqSpliterator implements Spliterator { + private final ArrayDeque deq; + private final int fence; // initially tail + private int index; // current index, modified on traverse/split + + /** Create new spliterator covering the given array and range */ + DeqSpliterator(ArrayDeque deq, int origin, int fence) { + this.deq = deq; this.index = origin; this.fence = fence; + } + + public DeqSpliterator trySplit() { + int n = deq.elements.length; + int h = index, t = fence; + if (h != t && ((h + 1) & (n - 1)) != t) { + if (h > t) + t += n; + int m = ((h + t) >>> 1) & (n - 1); + return new DeqSpliterator(deq, h, index = m); + } + return null; + } + + public void forEach(Consumer block) { + if (block == null) + throw new NullPointerException(); + Object[] a = deq.elements; + int m = a.length - 1, f = fence, i = index; + index = f; + while (i != f) { + @SuppressWarnings("unchecked") E e = (E)a[i]; + i = (i + 1) & m; + if (e == null) + throw new ConcurrentModificationException(); + block.accept(e); + } + } + + public boolean tryAdvance(Consumer block) { + if (block == null) + throw new NullPointerException(); + Object[] a = deq.elements; + int m = a.length - 1, i = index; + if (i != fence) { + @SuppressWarnings("unchecked") E e = (E)a[i]; + index = (i + 1) & m; + if (e == null) + throw new ConcurrentModificationException(); + block.accept(e); + return true; + } + return false; + } + + // Other spliterator methods + public long estimateSize() { + int n = fence - index; + if (n < 0) + n += deq.elements.length; + return (long)n; + } + public boolean hasExactSize() { return true; } + public boolean hasExactSplits() { return true; } } + }