--- jsr166/src/main/java/util/ArrayDeque.java 2005/05/16 06:16:12 1.9 +++ jsr166/src/main/java/util/ArrayDeque.java 2011/12/12 20:53:11 1.38 @@ -1,10 +1,9 @@ /* * Written by Josh Bloch of Google Inc. and released to the public domain, - * as explained at http://creativecommons.org/licenses/publicdomain. + * as explained at http://creativecommons.org/publicdomain/zero/1.0/. */ package java.util; -import java.io.*; /** * Resizable-array implementation of the {@link Deque} interface. Array @@ -44,7 +43,7 @@ import java.io.*; * Iterator} interfaces. * *

This class is a member of the - * + * * Java Collections Framework. * * @author Josh Bloch and Doug Lea @@ -52,7 +51,7 @@ 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. @@ -64,7 +63,7 @@ public class ArrayDeque extends Abstr * other. We also guarantee that all array cells not holding * deque elements are always null. */ - private transient E[] elements; + private transient Object[] elements; /** * The index of the element at the head of the deque (which is the @@ -108,7 +107,7 @@ 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]; } /** @@ -126,7 +125,7 @@ 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 +153,7 @@ public class ArrayDeque extends Abstr * sufficient to hold 16 elements. */ public ArrayDeque() { - elements = (E[]) new Object[16]; + elements = new Object[16]; } /** @@ -202,7 +201,8 @@ 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 +219,7 @@ 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 true (as specified by {@link Deque#offerFirst}) * @throws NullPointerException if the specified element is null */ public boolean offerFirst(E e) { @@ -231,7 +231,7 @@ 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 true (as specified by {@link Deque#offerLast}) * @throws NullPointerException if the specified element is null */ public boolean offerLast(E e) { @@ -261,7 +261,9 @@ 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 +273,8 @@ 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; @@ -283,28 +286,33 @@ 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)]; } /** @@ -313,8 +321,8 @@ public class ArrayDeque extends Abstr * 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). + * 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 @@ -324,7 +332,7 @@ public class ArrayDeque extends Abstr 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); @@ -341,8 +349,8 @@ public class ArrayDeque extends Abstr * 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). + * 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 @@ -352,7 +360,7 @@ public class ArrayDeque extends Abstr 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 +379,7 @@ 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 true (as specified by {@link Collection#add}) * @throws NullPointerException if the specified element is null */ public boolean add(E e) { @@ -385,7 +393,7 @@ 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 true (as specified by {@link Queue#offer}) * @throws NullPointerException if the specified element is null */ public boolean offer(E e) { @@ -394,7 +402,8 @@ 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}. @@ -422,8 +431,8 @@ 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}. * @@ -476,6 +485,14 @@ 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 +504,42 @@ 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 *** @@ -535,12 +568,16 @@ 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 +601,13 @@ 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); @@ -579,10 +617,48 @@ 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; } } @@ -599,7 +675,7 @@ public class ArrayDeque extends Abstr 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; @@ -613,8 +689,8 @@ public class ArrayDeque extends Abstr * 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). + * 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}. * @@ -645,39 +721,64 @@ public class ArrayDeque extends Abstr /** * Returns an array containing all of the elements in this deque - * 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 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 - * in the correct order */ public Object[] toArray() { - return copyElements(new Object[size()]); + return copyElements(new Object[size()]); } /** - * Returns an array containing all of the elements in this deque in the - * correct order; 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. + * 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: * - *

If the deque fits in the specified array with room to spare (i.e., - * the array has more elements than the deque), the element in the array - * immediately following the end of the collection is set to null. + * 

 {@code 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 the elements of the deque - * @throws ArrayStoreException if the runtime type of a is not a supertype - * of the runtime type of every element in this deque + * @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 */ + @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; @@ -692,50 +793,42 @@ 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, * 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 @@ -746,7 +839,6 @@ 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(); } }