--- jsr166/src/main/java/util/ArrayDeque.java 2005/05/17 06:36:47 1.11
+++ jsr166/src/main/java/util/ArrayDeque.java 2011/03/15 19:47:02 1.31
@@ -1,6 +1,6 @@
/*
* 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;
@@ -44,7 +44,7 @@ import java.io.*;
* Iterator} interfaces.
*
*
This class is a member of the
- *
+ *
* Java Collections Framework.
*
* @author Josh Bloch and Doug Lea
@@ -202,7 +202,8 @@ 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 +220,7 @@ 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 +232,7 @@ 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) {
@@ -313,8 +314,8 @@ 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
@@ -341,8 +342,8 @@ 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
@@ -371,7 +372,7 @@ 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 +386,7 @@ 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 +395,8 @@ 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 +424,8 @@ 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 +478,14 @@ 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 +497,42 @@ 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 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;
}
-
- // 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 +561,16 @@ 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 +594,12 @@ public class ArrayDeque extends Abstr
}
public E next() {
- E result;
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 = elements[cursor]) == null)
+ if (tail != fence || result == null)
throw new ConcurrentModificationException();
lastRet = cursor;
cursor = (cursor + 1) & (elements.length - 1);
@@ -579,10 +609,47 @@ 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);
+ 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;
- fence = tail;
}
}
@@ -613,8 +680,8 @@ 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}.
*
@@ -650,14 +717,14 @@ 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()]);
}
/**
@@ -702,7 +769,7 @@ public class ArrayDeque extends Abstr
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;
@@ -718,9 +785,7 @@ public class ArrayDeque extends Abstr
public ArrayDeque clone() {
try {
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) {
@@ -744,16 +809,12 @@ public class ArrayDeque extends Abstr
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;
- }
}
/**
@@ -772,6 +833,5 @@ 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();
-
}
}