--- jsr166/src/main/java/util/ArrayDeque.java 2005/09/15 16:55:24 1.17
+++ jsr166/src/main/java/util/ArrayDeque.java 2011/12/12 20:53:11 1.38
@@ -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 +261,9 @@ 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
@@ -273,7 +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;
@@ -285,28 +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)];
}
/**
@@ -326,7 +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);
@@ -354,7 +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);
@@ -479,6 +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
@@ -490,26 +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 ***
@@ -538,20 +568,12 @@ 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();
}
- /**
- * Returns an iterator over the elements in this deque in reverse
- * sequential order. The elements will be returned in order from
- * last (tail) to first (head).
- *
- * @return an iterator over the elements in this deque in reverse
- * sequence
- */
public Iterator descendingIterator() {
return new DescendingIterator();
}
@@ -579,12 +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);
@@ -594,49 +617,48 @@ 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;
}
}
@@ -653,7 +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;
@@ -711,7 +733,7 @@ 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()]);
}
/**
@@ -736,8 +758,7 @@ 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().
@@ -751,12 +772,13 @@ 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;
@@ -771,50 +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
@@ -825,7 +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();
}
}