--- jsr166/src/main/java/util/ArrayDeque.java 2005/09/16 11:15:41 1.19 +++ jsr166/src/main/java/util/ArrayDeque.java 2011/12/02 15:47:22 1.35 @@ -1,11 +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.util.*; // for javadoc (till 6280605 is fixed) -import java.io.*; /** * Resizable-array implementation of the {@link Deque} interface. Array @@ -45,7 +43,7 @@ import java.io.*; * Iterator} interfaces. * *

This class is a member of the - * + * * Java Collections Framework. * * @author Josh Bloch and Doug Lea @@ -53,7 +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. @@ -65,7 +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 @@ -109,7 +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]; } /** @@ -127,7 +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; } @@ -155,7 +153,7 @@ public class ArrayDeque extends Abstr * sufficient to hold 16 elements. */ public ArrayDeque() { - elements = (E[]) new Object[16]; + elements = new Object[16]; } /** @@ -263,7 +261,8 @@ 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 @@ -273,7 +272,7 @@ 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; @@ -285,28 +284,32 @@ 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)]; } /** @@ -326,7 +329,7 @@ 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); @@ -354,7 +357,7 @@ 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); @@ -479,6 +482,14 @@ 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 @@ -490,26 +501,42 @@ 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 *** @@ -571,12 +598,12 @@ 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); @@ -586,49 +613,47 @@ public class ArrayDeque extends Abstr public void remove() { if (lastRet < 0) throw new IllegalStateException(); - if (delete(lastRet)) // if left-shifted, undo increment in next() + if (delete(lastRet)) { // if left-shifted, undo increment in next() cursor = (cursor - 1) & (elements.length - 1); + fence = tail; + } lastRet = -1; - fence = tail; } } - private class DescendingIterator implements Iterator { /* * This class is nearly a mirror-image of DeqIterator, using - * (tail-1) instead of head for initial cursor, (head-1) - * instead of tail for fence, and elements.length instead of -1 - * for sentinel. It shares the same structure, but not many - * actual lines of code. + * tail instead of head for initial cursor, and head instead of + * tail for fence. */ - private int cursor = (tail - 1) & (elements.length - 1); - private int fence = (head - 1) & (elements.length - 1); - private int lastRet = elements.length; + private int cursor = tail; + private int fence = head; + private int lastRet = -1; public boolean hasNext() { return cursor != fence; } public E next() { - E result; if (cursor == fence) throw new NoSuchElementException(); - if (((head - 1) & (elements.length - 1)) != fence || - (result = elements[cursor]) == null) + cursor = (cursor - 1) & (elements.length - 1); + @SuppressWarnings("unchecked") E result = (E) elements[cursor]; + if (head != fence || result == null) throw new ConcurrentModificationException(); lastRet = cursor; - cursor = (cursor - 1) & (elements.length - 1); return result; } public void remove() { - if (lastRet >= elements.length) + if (lastRet < 0) throw new IllegalStateException(); - if (!delete(lastRet)) + if (!delete(lastRet)) { cursor = (cursor + 1) & (elements.length - 1); - lastRet = elements.length; - fence = (head - 1) & (elements.length - 1); + fence = head; + } + lastRet = -1; } } @@ -645,7 +670,7 @@ 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; @@ -703,7 +728,7 @@ public class ArrayDeque extends Abstr * @return an array containing all of the elements in this deque */ public Object[] toArray() { - return copyElements(new Object[size()]); + return copyElements(new Object[size()]); } /** @@ -728,8 +753,7 @@ public class ArrayDeque extends Abstr * The following code can be used to dump the deque into a newly * allocated array of 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(). @@ -743,12 +767,13 @@ 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; @@ -763,10 +788,9 @@ 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) { @@ -786,7 +810,8 @@ public class ArrayDeque extends Abstr * 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 @@ -801,8 +826,8 @@ public class ArrayDeque extends Abstr /** * Deserialize this deque. */ - 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 @@ -813,7 +838,6 @@ 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(); } }