--- jsr166/src/main/java/util/ArrayDeque.java 2005/03/22 01:29:00 1.5
+++ jsr166/src/main/java/util/ArrayDeque.java 2013/05/02 06:02:17 1.55
@@ -1,10 +1,12 @@
/*
* 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.*;
+import java.io.Serializable;
+import java.util.function.Consumer;
+import java.util.stream.Stream;
/**
* Resizable-array implementation of the {@link Deque} interface. Array
@@ -15,34 +17,39 @@ 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.
- * 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.
+ *
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
- * 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 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 arbitrary, non-deterministic behavior at
- * an undetermined time in the future.
+ *
The iterators returned by this class's {@link #iterator() 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
+ * {@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
+ * arbitrary, non-deterministic behavior at an undetermined time in the
+ * future.
*
*
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.
*
*
This class and its iterator implement all of the
- * optional methods of the {@link Collection} and {@link
- * Iterator} interfaces. This class is a member of the Java Collections
- * Framework.
+ * optional methods of the {@link Collection} and {@link
+ * Iterator} interfaces.
+ *
+ *
This class is a member of the
+ *
+ * Java Collections Framework.
*
* @author Josh Bloch and Doug Lea
* @since 1.6
@@ -61,20 +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.
@@ -85,9 +92,9 @@ 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.
+ * @param numElements the number of elements to hold
*/
private void allocateElements(int numElements) {
int initialCapacity = MIN_INITIAL_CAPACITY;
@@ -105,11 +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() {
@@ -123,35 +130,17 @@ 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;
}
/**
- * Copy the elements from our element array into the specified array,
- * in order (from first to last element in the deque). It is assumed
- * that the array is large enough to hold all elements in the deque.
- *
- * @return its argument
- */
- private T[] copyElements(T[] a) {
- if (head < tail) {
- System.arraycopy(elements, head, a, 0, size());
- } else if (head > tail) {
- int headPortionLen = elements.length - head;
- System.arraycopy(elements, head, a, 0, headPortionLen);
- System.arraycopy(elements, 0, a, headPortionLen, tail);
- }
- return a;
- }
-
- /**
* Constructs an empty array deque with an initial capacity
* sufficient to hold 16 elements.
*/
public ArrayDeque() {
- elements = (E[]) new Object[16];
+ elements = new Object[16];
}
/**
@@ -186,8 +175,8 @@ public class ArrayDeque extends Abstr
/**
* Inserts the specified element at the front of this deque.
*
- * @param e the element to insert
- * @throws NullPointerException if e is null
+ * @param e the element to add
+ * @throws NullPointerException if the specified element is null
*/
public void addFirst(E e) {
if (e == null)
@@ -198,12 +187,12 @@ public class ArrayDeque extends Abstr
}
/**
- * Inserts the specified element to the end of this deque.
- * This method is equivalent to {@link Collection#add} and
- * {@link #push}.
+ * Inserts the specified element at the end of this deque.
*
- * @param e the element to insert
- * @throws NullPointerException if e is null
+ * This method is equivalent to {@link #add}.
+ *
+ * @param e the element to add
+ * @throws NullPointerException if the specified element is null
*/
public void addLast(E e) {
if (e == null)
@@ -214,45 +203,11 @@ public class ArrayDeque extends Abstr
}
/**
- * Retrieves and removes the first element of this deque, or
- * null if this deque is empty.
- *
- * @return the first element of this deque, or null if
- * this deque is empty
- */
- public E pollFirst() {
- int h = head;
- E result = elements[h]; // Element is null if deque empty
- if (result == null)
- return null;
- elements[h] = null; // Must null out slot
- head = (h + 1) & (elements.length - 1);
- return result;
- }
-
- /**
- * Retrieves and removes the last element of this deque, or
- * null if this deque is empty.
- *
- * @return the last element of this deque, or null if
- * this deque is empty
- */
- public E pollLast() {
- int t = (tail - 1) & (elements.length - 1);
- E result = elements[t];
- if (result == null)
- return null;
- elements[t] = null;
- tail = t;
- return result;
- }
-
- /**
* Inserts the specified element at the front of this deque.
*
- * @param e the element to insert
- * @return true (as per the spec for {@link Deque#offerFirst})
- * @throws NullPointerException if e is null
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Deque#offerFirst})
+ * @throws NullPointerException if the specified element is null
*/
public boolean offerFirst(E e) {
addFirst(e);
@@ -260,11 +215,11 @@ public class ArrayDeque extends Abstr
}
/**
- * Inserts the specified element to the end of this deque.
+ * Inserts the specified element at the end of this deque.
*
- * @param e the element to insert
- * @return true (as per the spec for {@link Deque#offerLast})
- * @throws NullPointerException if e is null
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Deque#offerLast})
+ * @throws NullPointerException if the specified element is null
*/
public boolean offerLast(E e) {
addLast(e);
@@ -272,12 +227,7 @@ public class ArrayDeque extends Abstr
}
/**
- * Retrieves and removes the first element of this deque. This method
- * differs from the pollFirst method in that it throws an
- * exception if this deque is empty.
- *
- * @return the first element of this deque
- * @throws NoSuchElementException if this deque is empty
+ * @throws NoSuchElementException {@inheritDoc}
*/
public E removeFirst() {
E x = pollFirst();
@@ -287,12 +237,7 @@ public class ArrayDeque extends Abstr
}
/**
- * Retrieves and removes the last element of this deque. This method
- * differs from the pollLast method in that it throws an
- * exception if this deque is empty.
- *
- * @return the last element of this deque
- * @throws NoSuchElementException if this deque is empty
+ * @throws NoSuchElementException {@inheritDoc}
*/
public E removeLast() {
E x = pollLast();
@@ -301,74 +246,80 @@ public class ArrayDeque extends Abstr
return x;
}
- /**
- * Retrieves, but does not remove, the first element of this deque,
- * returning null if this deque is empty.
- *
- * @return the first element of this deque, or null if
- * this deque is empty
- */
- public E peekFirst() {
- return elements[head]; // elements[head] is null if deque empty
+ public E pollFirst() {
+ int h = head;
+ @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
+ head = (h + 1) & (elements.length - 1);
+ return result;
}
- /**
- * Retrieves, but does not remove, the last element of this deque,
- * returning null if this deque is empty.
- *
- * @return the last element of this deque, or null if this deque
- * is empty
- */
- public E peekLast() {
- return elements[(tail - 1) & (elements.length - 1)];
+ public E pollLast() {
+ int t = (tail - 1) & (elements.length - 1);
+ @SuppressWarnings("unchecked")
+ E result = (E) elements[t];
+ if (result == null)
+ return null;
+ elements[t] = null;
+ tail = t;
+ return result;
}
/**
- * Retrieves, but does not remove, the first element of this
- * deque. This method differs from the peekFirst method only
- * in that it throws an exception if this deque is empty.
- *
- * @return the first element of this deque
- * @throws NoSuchElementException if this deque is empty
+ * @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;
}
/**
- * Retrieves, but does not remove, the last element of this
- * deque. This method differs from the peekLast method only
- * in that it throws an exception if this deque is empty.
- *
- * @return the last element of this deque
- * @throws NoSuchElementException if this deque is empty
+ * @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() {
+ // elements[head] is null if deque empty
+ return (E) elements[head];
+ }
+
+ @SuppressWarnings("unchecked")
+ public E peekLast() {
+ 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). More
- * formally, removes the first element e such that (o==null ?
- * e==null : o.equals(e)). If the deque does not contain the
- * element, it is unchanged.
+ * 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 {@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);
@@ -381,20 +332,22 @@ public class ArrayDeque extends Abstr
/**
* Removes the last occurrence of the specified element in this
- * deque (when traversing the deque from head to tail). More
- * formally, removes the last element e such that (o==null ?
- * e==null : o.equals(e)). If the deque
- * does not contain the element, it is unchanged.
+ * 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 {@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);
@@ -408,26 +361,13 @@ public class ArrayDeque extends Abstr
// *** Queue methods ***
/**
- * Inserts the specified element to the end of this deque.
- *
- * This method is equivalent to {@link #offerLast}.
- *
- * @param e the element to insert
- * @return true (as per the spec for {@link Queue#offer})
- * @throws NullPointerException if e is null
- */
- public boolean offer(E e) {
- return offerLast(e);
- }
-
- /**
- * Inserts the specified element to the end of this deque.
+ * Inserts the specified element at the end of this deque.
*
*
This method is equivalent to {@link #addLast}.
*
- * @param e the element to insert
- * @return true (as per the spec for {@link Collection#add})
- * @throws NullPointerException if e is null
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Collection#add})
+ * @throws NullPointerException if the specified element is null
*/
public boolean add(E e) {
addLast(e);
@@ -435,61 +375,74 @@ public class ArrayDeque extends Abstr
}
/**
- * Retrieves and removes the head of the queue represented by
- * this deque, or null if this deque is empty. In other words,
- * retrieves and removes the first element of this deque, or null
- * if this deque is empty.
+ * Inserts the specified element at the end of this deque.
*
- * This method is equivalent to {@link #pollFirst}.
+ *
This method is equivalent to {@link #offerLast}.
*
- * @return the first element of this deque, or null if
- * this deque is empty
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Queue#offer})
+ * @throws NullPointerException if the specified element is null
*/
- public E poll() {
- return pollFirst();
+ public boolean offer(E e) {
+ return offerLast(e);
}
/**
* Retrieves and removes the head of the queue represented by this deque.
- * This method differs from the poll method 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}.
*
* @return the head of the queue represented by this deque
- * @throws NoSuchElementException if this deque is empty
+ * @throws NoSuchElementException {@inheritDoc}
*/
public E remove() {
return removeFirst();
}
/**
- * Retrieves, but does not remove, the head of the queue represented by
- * this deque, returning null if this deque is empty.
+ * Retrieves and removes the head of the queue represented by this deque
+ * (in other words, the first element of this deque), or returns
+ * {@code null} if this deque is empty.
*
- *
This method is equivalent to {@link #peekFirst}
+ *
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 peek() {
- return peekFirst();
+ public E poll() {
+ return pollFirst();
}
/**
* Retrieves, but does not remove, the head of the queue represented by
- * this deque. This method differs from the peek method only in
+ * 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}
+ *
This method is equivalent to {@link #getFirst}.
*
* @return the head of the queue represented by this deque
- * @throws NoSuchElementException if this deque is empty
+ * @throws NoSuchElementException {@inheritDoc}
*/
public E element() {
return getFirst();
}
+ /**
+ * Retrieves, but does not remove, the head of the queue represented by
+ * 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
+ * {@code null} if this deque is empty
+ */
+ public E peek() {
+ return peekFirst();
+ }
+
// *** Stack methods ***
/**
@@ -499,7 +452,7 @@ public class ArrayDeque extends Abstr
* This method is equivalent to {@link #addFirst}.
*
* @param e the element to push
- * @throws NullPointerException if e is null
+ * @throws NullPointerException if the specified element is null
*/
public void push(E e) {
addFirst(e);
@@ -512,38 +465,68 @@ public class ArrayDeque extends Abstr
* This method is equivalent to {@link #removeFirst()}.
*
* @return the element at the front of this deque (which is the top
- * of the stack represented by this deque)
- * @throws NoSuchElementException if this deque is empty
+ * of the stack represented by this deque)
+ * @throws NoSuchElementException {@inheritDoc}
*/
public E pop() {
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;
+ }
+
/**
- * Remove the element at the specified position in the elements array,
- * adjusting head, tail, and size as necessary. This can result in
- * motion of elements backwards or forwards in the array.
+ * Removes the element at the specified position in the elements array,
+ * adjusting head and tail as necessary. This can result in motion of
+ * elements backwards or forwards in the array.
*
*
This method is called delete rather than remove to emphasize
- * that its semantics differ from those of List.remove(int).
+ * that its semantics differ from those of {@link List#remove(int)}.
*
* @return true if elements moved backwards
*/
private boolean delete(int i) {
- // Case 1: Deque doesn't wrap
- // Case 2: Deque does wrap and removed element is in the head portion
- if ((head < tail || tail == 0) || i >= head) {
- System.arraycopy(elements, head, elements, head + 1, i - head);
- elements[head] = null;
- head = (head + 1) & (elements.length - 1);
+ 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 ***
@@ -558,9 +541,9 @@ public class ArrayDeque extends Abstr
}
/**
- * Returns true if this collection contains no elements.
+ * Returns {@code true} if this deque contains no elements.
*
- * @return true if this collection contains no elements.
+ * @return {@code true} if this deque contains no elements
*/
public boolean isEmpty() {
return head == tail;
@@ -572,12 +555,16 @@ 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.
@@ -601,12 +588,13 @@ 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);
@@ -616,28 +604,65 @@ 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;
+ }
+ }
+
+ /**
+ * 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 class DescendingIterator implements Iterator {
+ 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
- * e.equals(o).
+ * 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;
@@ -648,17 +673,24 @@ public class ArrayDeque extends Abstr
/**
* Removes a single instance of the specified element from this deque.
- * This method is equivalent to {@link #removeFirstOccurrence}.
+ * If the deque does not contain the element, it is unchanged.
+ * 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(Object)}.
*
- * @param e element to be removed from this deque, if present
- * @return true if this deque contained the specified element
+ * @param o element to be removed from this deque, if present
+ * @return {@code true} if this deque contained the specified element
*/
- public boolean remove(Object e) {
- return removeFirstOccurrence(e);
+ public boolean remove(Object o) {
+ return removeFirstOccurrence(o);
}
/**
* Removes all of the elements from this deque.
+ * The deque will be empty after this call returns.
*/
public void clear() {
int h = head;
@@ -670,47 +702,88 @@ public class ArrayDeque extends Abstr
do {
elements[i] = null;
i = (i + 1) & mask;
- } while(i != t);
+ } while (i != t);
}
}
/**
* 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()]);
+ final int head = this.head;
+ final int tail = this.tail;
+ boolean wrap = (tail < head);
+ int end = wrap ? tail + elements.length : tail;
+ Object[] a = Arrays.copyOfRange(elements, head, end);
+ if (wrap)
+ System.arraycopy(elements, 0, a, elements.length - head, tail);
+ return a;
}
/**
- * 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
+ * {@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 {@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 {@code String}:
+ *
+ *
{@code String[] y = x.toArray(new String[0]);}
*
- * 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.
+ * 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
- * 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
+ * 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 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);
- if (a.length > size)
- a[size] = null;
+ final int head = this.head;
+ final int tail = this.tail;
+ boolean wrap = (tail < head);
+ int size = (tail - head) + (wrap ? elements.length : 0);
+ int firstLeg = size - (wrap ? tail : 0);
+ int len = a.length;
+ if (size > len) {
+ a = (T[]) Arrays.copyOfRange(elements, head, head + size,
+ a.getClass());
+ } else {
+ System.arraycopy(elements, head, a, 0, firstLeg);
+ if (size < len)
+ a[size] = null;
+ }
+ if (wrap)
+ System.arraycopy(elements, 0, a, firstLeg, tail);
return a;
}
@@ -723,50 +796,42 @@ 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
@@ -777,7 +842,88 @@ 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 Spliterator spliterator() {
+ return new DeqSpliterator(this, -1, -1);
+ }
+ static final class DeqSpliterator implements Spliterator {
+ private final ArrayDeque deq;
+ private int fence; // -1 until first use
+ private int index; // current index, modified on traverse/split
+
+ /** Creates new spliterator covering the given array and range */
+ DeqSpliterator(ArrayDeque deq, int origin, int fence) {
+ this.deq = deq;
+ this.index = origin;
+ this.fence = fence;
+ }
+
+ private int getFence() { // force initialization
+ int t;
+ if ((t = fence) < 0) {
+ t = fence = deq.tail;
+ index = deq.head;
+ }
+ return t;
+ }
+
+ public Spliterator trySplit() {
+ int t = getFence(), h = index, n = deq.elements.length;
+ 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 forEachRemaining(Consumer consumer) {
+ if (consumer == null)
+ throw new NullPointerException();
+ Object[] a = deq.elements;
+ int m = a.length - 1, f = getFence(), i = index;
+ index = f;
+ while (i != f) {
+ @SuppressWarnings("unchecked") E e = (E)a[i];
+ i = (i + 1) & m;
+ if (e == null)
+ throw new ConcurrentModificationException();
+ consumer.accept(e);
+ }
+ }
+
+ public boolean tryAdvance(Consumer consumer) {
+ if (consumer == null)
+ throw new NullPointerException();
+ Object[] a = deq.elements;
+ int m = a.length - 1, f = getFence(), i = index;
+ if (i != fence) {
+ @SuppressWarnings("unchecked") E e = (E)a[i];
+ index = (i + 1) & m;
+ if (e == null)
+ throw new ConcurrentModificationException();
+ consumer.accept(e);
+ return true;
+ }
+ return false;
+ }
+
+ public long estimateSize() {
+ int n = getFence() - index;
+ if (n < 0)
+ n += deq.elements.length;
+ return (long) n;
+ }
+
+ @Override
+ public int characteristics() {
+ return Spliterator.ORDERED | Spliterator.SIZED |
+ Spliterator.NONNULL | Spliterator.SUBSIZED;
+ }
}
+
}