--- jsr166/src/main/java/util/ArrayDeque.java 2011/12/02 15:47:22 1.35
+++ jsr166/src/main/java/util/ArrayDeque.java 2016/11/05 16:21:06 1.109
@@ -5,6 +5,11 @@
package java.util;
+import java.io.Serializable;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+import java.util.function.UnaryOperator;
+
/**
* Resizable-array implementation of the {@link Deque} interface. Array
* deques have no capacity restrictions; they grow as necessary to support
@@ -14,17 +19,19 @@ package java.util;
* {@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
+ *
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
@@ -33,7 +40,7 @@ package java.util;
*
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.
@@ -47,105 +54,122 @@ package java.util;
* Java Collections Framework.
*
* @author Josh Bloch and Doug Lea
+ * @param the type of elements held in this deque
* @since 1.6
- * @param the type of elements held in this collection
*/
public class ArrayDeque extends AbstractCollection
- implements Deque, Cloneable, java.io.Serializable
+ implements Deque, Cloneable, Serializable
{
+ /*
+ * VMs excel at optimizing simple array loops where indices are
+ * incrementing or decrementing over a valid slice, e.g.
+ *
+ * for (int i = start; i < end; i++) ... elements[i]
+ *
+ * Because in a circular array, elements are in general stored in
+ * two disjoint such slices, we help the VM by writing unusual
+ * nested loops for all traversals over the elements.
+ */
+
/**
* The array in which the elements of the deque are stored.
- * The capacity of the deque is the length of this array, which is
- * always a power of two. The array is never allowed to become
- * full, except transiently within an addX method where it is
- * resized (see doubleCapacity) immediately upon becoming full,
- * thus avoiding head and tail wrapping around to equal each
- * other. We also guarantee that all array cells not holding
- * deque elements are always null.
+ * We guarantee that all array cells not holding deque elements
+ * are always null.
*/
- private transient Object[] elements;
+ transient Object[] elements;
/**
* 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.
+ * arbitrary number 0 <= head < elements.length 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.
- * Must be a power of 2.
- */
- private static final int MIN_INITIAL_CAPACITY = 8;
-
- // ****** Array allocation and resizing utilities ******
-
- /**
- * Allocate empty array to hold the given number of elements.
- *
- * @param numElements the number of elements to hold
- */
- private void allocateElements(int numElements) {
- int initialCapacity = MIN_INITIAL_CAPACITY;
- // Find the best power of two to hold elements.
- // Tests "<=" because arrays aren't kept full.
- if (numElements >= initialCapacity) {
- initialCapacity = numElements;
- initialCapacity |= (initialCapacity >>> 1);
- initialCapacity |= (initialCapacity >>> 2);
- initialCapacity |= (initialCapacity >>> 4);
- initialCapacity |= (initialCapacity >>> 8);
- initialCapacity |= (initialCapacity >>> 16);
- initialCapacity++;
+ * The maximum size of array to allocate.
+ * Some VMs reserve some header words in an array.
+ * Attempts to allocate larger arrays may result in
+ * OutOfMemoryError: Requested array size exceeds VM limit
+ */
+ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
+
+ /**
+ * Increases the capacity of this deque by at least the given amount.
+ *
+ * @param needed the required minimum extra capacity; must be positive
+ */
+ private void grow(int needed) {
+ // overflow-conscious code
+ final int oldCapacity = elements.length;
+ int newCapacity;
+ // Double capacity if small; else grow by 50%
+ int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
+ if (jump < needed
+ || (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
+ newCapacity = newCapacity(needed, jump);
+ elements = Arrays.copyOf(elements, newCapacity);
+ // Exceptionally, here tail == head needs to be disambiguated
+ if (tail < head || (tail == head && elements[head] != null)) {
+ // wrap around; slide first leg forward to end of array
+ int newSpace = newCapacity - oldCapacity;
+ System.arraycopy(elements, head,
+ elements, head + newSpace,
+ oldCapacity - head);
+ Arrays.fill(elements, head, head + newSpace, null);
+ head += newSpace;
+ }
+ // checkInvariants();
+ }
- if (initialCapacity < 0) // Too many elements, must back off
- initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
+ /** Capacity calculation for edge conditions, especially overflow. */
+ private int newCapacity(int needed, int jump) {
+ final int oldCapacity = elements.length, minCapacity;
+ if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
+ if (minCapacity < 0)
+ throw new IllegalStateException("Sorry, deque too big");
+ return Integer.MAX_VALUE;
}
- elements = new Object[initialCapacity];
+ if (needed > jump)
+ return minCapacity;
+ return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
+ ? oldCapacity + jump
+ : MAX_ARRAY_SIZE;
}
/**
- * Double the capacity of this deque. Call only when full, i.e.,
- * when head and tail have wrapped around to become equal.
+ * Increases the internal storage of this collection, if necessary,
+ * to ensure that it can hold at least the given number of elements.
+ *
+ * @param minCapacity the desired minimum capacity
+ * @since TBD
*/
- private void doubleCapacity() {
- assert head == tail;
- int p = head;
- int n = elements.length;
- int r = n - p; // number of elements to the right of p
- int newCapacity = n << 1;
- if (newCapacity < 0)
- throw new IllegalStateException("Sorry, deque too big");
- Object[] a = new Object[newCapacity];
- System.arraycopy(elements, p, a, 0, r);
- System.arraycopy(elements, 0, a, r, p);
- elements = a;
- head = 0;
- tail = n;
+ /* public */ void ensureCapacity(int minCapacity) {
+ int needed;
+ if ((needed = (minCapacity + 1 - elements.length)) > 0)
+ grow(needed);
+ // checkInvariants();
}
/**
- * Copies 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.
+ * Minimizes the internal storage of this collection.
*
- * @return its argument
+ * @since TBD
*/
- 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);
+ /* public */ void trimToSize() {
+ int size;
+ if ((size = size()) + 1 < elements.length) {
+ elements = toArray(new Object[size + 1]);
+ head = 0;
+ tail = size;
}
- return a;
+ // checkInvariants();
}
/**
@@ -160,10 +184,10 @@ public class ArrayDeque extends Abstr
* Constructs an empty array deque with an initial capacity
* sufficient to hold the specified number of elements.
*
- * @param numElements lower bound on initial capacity of the deque
+ * @param numElements lower bound on initial capacity of the deque
*/
public ArrayDeque(int numElements) {
- allocateElements(numElements);
+ elements = new Object[Math.max(1, numElements + 1)];
}
/**
@@ -177,10 +201,69 @@ public class ArrayDeque extends Abstr
* @throws NullPointerException if the specified collection is null
*/
public ArrayDeque(Collection c) {
- allocateElements(c.size());
+ elements = new Object[c.size() + 1];
addAll(c);
}
+ /**
+ * Increments i, mod modulus.
+ * Precondition and postcondition: 0 <= i < modulus.
+ */
+ static final int inc(int i, int modulus) {
+ if (++i >= modulus) i = 0;
+ return i;
+ }
+
+ /**
+ * Decrements i, mod modulus.
+ * Precondition and postcondition: 0 <= i < modulus.
+ */
+ static final int dec(int i, int modulus) {
+ if (--i < 0) i = modulus - 1;
+ return i;
+ }
+
+ /**
+ * Adds i and j, mod modulus.
+ * Precondition and postcondition: 0 <= i < modulus, 0 <= j <= modulus.
+ */
+ static final int add(int i, int j, int modulus) {
+ if ((i += j) - modulus >= 0) i -= modulus;
+ return i;
+ }
+
+ /**
+ * Subtracts j from i, mod modulus.
+ * Index i must be logically ahead of j.
+ * Returns the "circular distance" from j to i.
+ * Precondition and postcondition: 0 <= i < modulus, 0 <= j < modulus.
+ */
+ static final int sub(int i, int j, int modulus) {
+ if ((i -= j) < 0) i += modulus;
+ return i;
+ }
+
+ /**
+ * Returns element at array index i.
+ * This is a slight abuse of generics, accepted by javac.
+ */
+ @SuppressWarnings("unchecked")
+ static final E elementAt(Object[] es, int i) {
+ return (E) es[i];
+ }
+
+ /**
+ * A version of elementAt that checks for null elements.
+ * This check doesn't catch all possible comodifications,
+ * but does catch ones that corrupt traversal.
+ */
+ static final E nonNullElementAt(Object[] es, int i) {
+ @SuppressWarnings("unchecked") E e = (E) es[i];
+ if (e == null)
+ throw new ConcurrentModificationException();
+ return e;
+ }
+
// The main insertion and extraction methods are addFirst,
// addLast, pollFirst, pollLast. The other methods are defined in
// terms of these.
@@ -194,9 +277,11 @@ public class ArrayDeque extends Abstr
public void addFirst(E e) {
if (e == null)
throw new NullPointerException();
- elements[head = (head - 1) & (elements.length - 1)] = e;
+ final Object[] es = elements;
+ es[head = dec(head, es.length)] = e;
if (head == tail)
- doubleCapacity();
+ grow(1);
+ // checkInvariants();
}
/**
@@ -210,16 +295,38 @@ public class ArrayDeque extends Abstr
public void addLast(E e) {
if (e == null)
throw new NullPointerException();
- elements[tail] = e;
- if ( (tail = (tail + 1) & (elements.length - 1)) == head)
- doubleCapacity();
+ final Object[] es = elements;
+ es[tail] = e;
+ if (head == (tail = inc(tail, es.length)))
+ grow(1);
+ // checkInvariants();
+ }
+
+ /**
+ * Adds all of the elements in the specified collection at the end
+ * of this deque, as if by calling {@link #addLast} on each one,
+ * in the order that they are returned by the collection's
+ * iterator.
+ *
+ * @param c the elements to be inserted into this deque
+ * @return {@code true} if this deque changed as a result of the call
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
+ */
+ public boolean addAll(Collection c) {
+ final int s = size(), needed;
+ if ((needed = s + c.size() - elements.length + 1) > 0)
+ grow(needed);
+ c.forEach((e) -> addLast(e));
+ // checkInvariants();
+ return size() > s;
}
/**
* Inserts the specified element at the front of this deque.
*
* @param e the element to add
- * @return true (as specified by {@link Deque#offerFirst})
+ * @return {@code true} (as specified by {@link Deque#offerFirst})
* @throws NullPointerException if the specified element is null
*/
public boolean offerFirst(E e) {
@@ -231,7 +338,7 @@ public class ArrayDeque extends Abstr
* Inserts the specified element at the end of this deque.
*
* @param e the element to add
- * @return true (as specified by {@link Deque#offerLast})
+ * @return {@code true} (as specified by {@link Deque#offerLast})
* @throws NullPointerException if the specified element is null
*/
public boolean offerLast(E e) {
@@ -243,99 +350,104 @@ public class ArrayDeque extends Abstr
* @throws NoSuchElementException {@inheritDoc}
*/
public E removeFirst() {
- E x = pollFirst();
- if (x == null)
+ E e = pollFirst();
+ if (e == null)
throw new NoSuchElementException();
- return x;
+ // checkInvariants();
+ return e;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E removeLast() {
- E x = pollLast();
- if (x == null)
+ E e = pollLast();
+ if (e == null)
throw new NoSuchElementException();
- return x;
+ // checkInvariants();
+ return e;
}
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;
+ final Object[] es;
+ final int h;
+ E e = elementAt(es = elements, h = head);
+ if (e != null) {
+ es[h] = null;
+ head = inc(h, es.length);
+ }
+ // checkInvariants();
+ return e;
}
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;
+ final Object[] es;
+ final int t;
+ E e = elementAt(es = elements, t = dec(tail, es.length));
+ if (e != null)
+ es[tail = t] = null;
+ // checkInvariants();
+ return e;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E getFirst() {
- @SuppressWarnings("unchecked") E result = (E) elements[head];
- if (result == null)
+ E e = elementAt(elements, head);
+ if (e == null)
throw new NoSuchElementException();
- return result;
+ // checkInvariants();
+ return e;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E getLast() {
- @SuppressWarnings("unchecked")
- E result = (E) elements[(tail - 1) & (elements.length - 1)];
- if (result == null)
+ final Object[] es = elements;
+ E e = elementAt(es, dec(tail, es.length));
+ if (e == null)
throw new NoSuchElementException();
- return result;
+ // checkInvariants();
+ return e;
}
- @SuppressWarnings("unchecked")
public E peekFirst() {
- // elements[head] is null if deque empty
- return (E) elements[head];
+ // checkInvariants();
+ return elementAt(elements, head);
}
- @SuppressWarnings("unchecked")
public E peekLast() {
- return (E) elements[(tail - 1) & (elements.length - 1)];
+ // checkInvariants();
+ final Object[] es;
+ return elementAt(es = elements, dec(tail, es.length));
}
/**
* Removes the first occurrence of the specified element in this
* 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 e such that
- * o.equals(e) (if such an element exists).
- * Returns true if this deque contained the specified element
+ * 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;
- Object x;
- while ( (x = elements[i]) != null) {
- if (o.equals(x)) {
- delete(i);
- return true;
+ if (o != null) {
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ if (o.equals(es[i])) {
+ delete(i);
+ return true;
+ }
+ if (to == end) break;
}
- i = (i + 1) & mask;
}
return false;
}
@@ -344,26 +456,26 @@ public class ArrayDeque extends Abstr
* Removes the last occurrence of the specified element in this
* 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 e such that
- * o.equals(e) (if such an element exists).
- * Returns true if this deque contained the specified element
+ * 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;
- Object x;
- while ( (x = elements[i]) != null) {
- if (o.equals(x)) {
- delete(i);
- return true;
+ if (o != null) {
+ final Object[] es = elements;
+ for (int i = tail, end = head, to = (i >= end) ? end : 0;
+ ; i = es.length, to = end) {
+ while (--i >= to)
+ if (o.equals(es[i])) {
+ delete(i);
+ return true;
+ }
+ if (to == end) break;
}
- i = (i - 1) & mask;
}
return false;
}
@@ -376,7 +488,7 @@ public class ArrayDeque extends Abstr
* This method is equivalent to {@link #addLast}.
*
* @param e the element to add
- * @return true (as specified by {@link Collection#add})
+ * @return {@code true} (as specified by {@link Collection#add})
* @throws NullPointerException if the specified element is null
*/
public boolean add(E e) {
@@ -390,7 +502,7 @@ public class ArrayDeque extends Abstr
* This method is equivalent to {@link #offerLast}.
*
* @param e the element to add
- * @return true (as specified by {@link Queue#offer})
+ * @return {@code true} (as specified by {@link Queue#offer})
* @throws NullPointerException if the specified element is null
*/
public boolean offer(E e) {
@@ -415,12 +527,12 @@ public class ArrayDeque extends Abstr
/**
* Retrieves and removes the head of the queue represented by this deque
* (in other words, the first element of this deque), or returns
- * null if this deque is empty.
+ * {@code null} if this deque is empty.
*
* 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 poll() {
return pollFirst();
@@ -442,12 +554,12 @@ public class ArrayDeque extends Abstr
/**
* Retrieves, but does not remove, the head of the queue represented by
- * this deque, or returns null if this deque is empty.
+ * 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
- * null if this deque is empty
+ * {@code null} if this deque is empty
*/
public E peek() {
return peekFirst();
@@ -482,59 +594,50 @@ 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
- * elements backwards or forwards in the array.
+ * Removes the element at the specified position in the elements array.
+ * This can result in forward or backwards motion of array elements.
+ * We optimize for least element motion.
*
* This method is called delete rather than remove to emphasize
* that its semantics differ from those of {@link List#remove(int)}.
*
- * @return true if elements moved backwards
+ * @return true if elements near tail moved backwards
*/
- private boolean delete(int i) {
- checkInvariants();
- final Object[] elements = this.elements;
- final int mask = elements.length - 1;
+ boolean delete(int i) {
+ // checkInvariants();
+ final Object[] es = elements;
+ final int capacity = es.length;
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
+ // number of elements before to-be-deleted elt
+ final int front = sub(i, h, capacity);
+ final int back = size() - front - 1; // number of elements after
if (front < back) {
+ // move front elements forwards
if (h <= i) {
- System.arraycopy(elements, h, elements, h + 1, front);
+ System.arraycopy(es, h, es, 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);
+ System.arraycopy(es, 0, es, 1, i);
+ es[0] = es[capacity - 1];
+ System.arraycopy(es, h, es, h + 1, front - (i + 1));
}
- elements[h] = null;
- head = (h + 1) & mask;
+ es[h] = null;
+ head = inc(h, capacity);
+ // checkInvariants();
return false;
} else {
- if (i < t) { // Copy the null tail as well
- System.arraycopy(elements, i + 1, elements, i, back);
- tail = t - 1;
+ // move back elements backwards
+ tail = dec(tail, capacity);
+ if (i <= tail) {
+ System.arraycopy(es, i + 1, es, i, back);
} 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;
+ int firstLeg = capacity - (i + 1);
+ System.arraycopy(es, i + 1, es, i, firstLeg);
+ es[capacity - 1] = es[0];
+ System.arraycopy(es, 1, es, 0, back - firstLeg - 1);
}
+ es[tail] = null;
+ // checkInvariants();
return true;
}
}
@@ -547,13 +650,13 @@ public class ArrayDeque extends Abstr
* @return the number of elements in this deque
*/
public int size() {
- return (tail - head) & (elements.length - 1);
+ return sub(tail, head, elements.length);
}
/**
- * Returns true if this deque contains no elements.
+ * Returns {@code true} if this deque contains no elements.
*
- * @return true if this deque contains no elements
+ * @return {@code true} if this deque contains no elements
*/
public boolean isEmpty() {
return head == tail;
@@ -576,105 +679,344 @@ public class ArrayDeque extends Abstr
}
private class DeqIterator implements Iterator {
- /**
- * Index of element to be returned by subsequent call to next.
- */
- private int cursor = head;
+ /** Index of element to be returned by subsequent call to next. */
+ int cursor;
- /**
- * Tail recorded at construction (also in remove), to stop
- * iterator and also to check for comodification.
- */
- private int fence = tail;
+ /** Number of elements yet to be returned. */
+ int remaining = size();
/**
* Index of element returned by most recent call to next.
* Reset to -1 if element is deleted by a call to remove.
*/
- private int lastRet = -1;
+ int lastRet = -1;
+
+ DeqIterator() { cursor = head; }
- public boolean hasNext() {
- return cursor != fence;
+ public final boolean hasNext() {
+ return remaining > 0;
}
public E next() {
- if (cursor == fence)
+ if (remaining <= 0)
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 == null)
- throw new ConcurrentModificationException();
+ final Object[] es = elements;
+ E e = nonNullElementAt(es, cursor);
lastRet = cursor;
- cursor = (cursor + 1) & (elements.length - 1);
- return result;
+ cursor = inc(cursor, es.length);
+ remaining--;
+ return e;
}
- public void remove() {
+ void postDelete(boolean leftShifted) {
+ if (leftShifted)
+ cursor = dec(cursor, elements.length);
+ }
+
+ public final void remove() {
if (lastRet < 0)
throw new IllegalStateException();
- if (delete(lastRet)) { // if left-shifted, undo increment in next()
- cursor = (cursor - 1) & (elements.length - 1);
- fence = tail;
- }
+ postDelete(delete(lastRet));
lastRet = -1;
}
+
+ public void forEachRemaining(Consumer action) {
+ Objects.requireNonNull(action);
+ int r;
+ if ((r = remaining) <= 0)
+ return;
+ remaining = 0;
+ final Object[] es = elements;
+ if (es[cursor] == null || sub(tail, cursor, es.length) != r)
+ throw new ConcurrentModificationException();
+ for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ action.accept(elementAt(es, i));
+ if (to == end) {
+ if (end != tail)
+ throw new ConcurrentModificationException();
+ lastRet = dec(end, es.length);
+ break;
+ }
+ }
+ }
}
- 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;
+ private class DescendingIterator extends DeqIterator {
+ DescendingIterator() { cursor = dec(tail, elements.length); }
- public boolean hasNext() {
- return cursor != fence;
+ public final E next() {
+ if (remaining <= 0)
+ throw new NoSuchElementException();
+ final Object[] es = elements;
+ E e = nonNullElementAt(es, cursor);
+ lastRet = cursor;
+ cursor = dec(cursor, es.length);
+ remaining--;
+ return e;
}
- 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)
+ void postDelete(boolean leftShifted) {
+ if (!leftShifted)
+ cursor = inc(cursor, elements.length);
+ }
+
+ public final void forEachRemaining(Consumer action) {
+ Objects.requireNonNull(action);
+ int r;
+ if ((r = remaining) <= 0)
+ return;
+ remaining = 0;
+ final Object[] es = elements;
+ if (es[cursor] == null || sub(cursor, head, es.length) + 1 != r)
throw new ConcurrentModificationException();
- lastRet = cursor;
- return result;
+ for (int i = cursor, end = head, to = (i >= end) ? end : 0;
+ ; i = es.length - 1, to = end) {
+ for (; i >= to; i--)
+ action.accept(elementAt(es, i));
+ if (to == end) {
+ if (end != head)
+ throw new ConcurrentModificationException();
+ lastRet = head;
+ break;
+ }
+ }
+ }
+ }
+
+ /**
+ * Creates a late-binding
+ * and fail-fast {@link Spliterator} over the elements in this
+ * deque.
+ *
+ * The {@code Spliterator} reports {@link Spliterator#SIZED},
+ * {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
+ * {@link Spliterator#NONNULL}. Overriding implementations should document
+ * the reporting of additional characteristic values.
+ *
+ * @return a {@code Spliterator} over the elements in this deque
+ * @since 1.8
+ */
+ public Spliterator spliterator() {
+ return new DeqSpliterator();
+ }
+
+ final class DeqSpliterator implements Spliterator {
+ private int fence; // -1 until first use
+ private int cursor; // current index, modified on traverse/split
+
+ /** Constructs late-binding spliterator over all elements. */
+ DeqSpliterator() {
+ this.fence = -1;
}
- public void remove() {
- if (lastRet < 0)
- throw new IllegalStateException();
- if (!delete(lastRet)) {
- cursor = (cursor + 1) & (elements.length - 1);
- fence = head;
+ /** Constructs spliterator over the given range. */
+ DeqSpliterator(int origin, int fence) {
+ this.cursor = origin;
+ this.fence = fence;
+ }
+
+ /** Ensures late-binding initialization; then returns fence. */
+ private int getFence() { // force initialization
+ int t;
+ if ((t = fence) < 0) {
+ t = fence = tail;
+ cursor = head;
+ }
+ return t;
+ }
+
+ public DeqSpliterator trySplit() {
+ final Object[] es = elements;
+ final int i, n;
+ return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
+ ? null
+ : new DeqSpliterator(i, cursor = add(i, n, es.length));
+ }
+
+ public void forEachRemaining(Consumer action) {
+ if (action == null)
+ throw new NullPointerException();
+ final int end = getFence(), cursor = this.cursor;
+ final Object[] es = elements;
+ if (cursor != end) {
+ this.cursor = end;
+ // null check at both ends of range is sufficient
+ if (es[cursor] == null || es[dec(end, es.length)] == null)
+ throw new ConcurrentModificationException();
+ for (int i = cursor, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ action.accept(elementAt(es, i));
+ if (to == end) break;
+ }
+ }
+ }
+
+ public boolean tryAdvance(Consumer action) {
+ if (action == null)
+ throw new NullPointerException();
+ int t, i;
+ if ((t = fence) < 0) t = getFence();
+ if (t == (i = cursor))
+ return false;
+ final Object[] es;
+ action.accept(nonNullElementAt(es = elements, i));
+ cursor = inc(i, es.length);
+ return true;
+ }
+
+ public long estimateSize() {
+ return sub(getFence(), cursor, elements.length);
+ }
+
+ public int characteristics() {
+ return Spliterator.NONNULL
+ | Spliterator.ORDERED
+ | Spliterator.SIZED
+ | Spliterator.SUBSIZED;
+ }
+ }
+
+ public void forEach(Consumer action) {
+ Objects.requireNonNull(action);
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ action.accept(elementAt(es, i));
+ if (to == end) {
+ if (end != tail) throw new ConcurrentModificationException();
+ break;
+ }
+ }
+ // checkInvariants();
+ }
+
+ /**
+ * Replaces each element of this deque with the result of applying the
+ * operator to that element, as specified by {@link List#replaceAll}.
+ *
+ * @param operator the operator to apply to each element
+ * @since TBD
+ */
+ /* public */ void replaceAll(UnaryOperator operator) {
+ Objects.requireNonNull(operator);
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ es[i] = operator.apply(elementAt(es, i));
+ if (to == end) {
+ if (end != tail) throw new ConcurrentModificationException();
+ break;
+ }
+ }
+ // checkInvariants();
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean removeIf(Predicate filter) {
+ Objects.requireNonNull(filter);
+ return bulkRemove(filter);
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean removeAll(Collection c) {
+ Objects.requireNonNull(c);
+ return bulkRemove(e -> c.contains(e));
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean retainAll(Collection c) {
+ Objects.requireNonNull(c);
+ return bulkRemove(e -> !c.contains(e));
+ }
+
+ /** Implementation of bulk remove methods. */
+ private boolean bulkRemove(Predicate filter) {
+ // checkInvariants();
+ final Object[] es = elements;
+ // Optimize for initial run of survivors
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ if (filter.test(elementAt(es, i)))
+ return bulkRemoveModified(filter, i, to);
+ if (to == end) {
+ if (end != tail) throw new ConcurrentModificationException();
+ break;
}
- lastRet = -1;
+ }
+ return false;
+ }
+
+ /**
+ * Helper for bulkRemove, in case of at least one deletion.
+ * @param i valid index of first element to be deleted
+ */
+ private boolean bulkRemoveModified(
+ Predicate filter, int i, int to) {
+ final Object[] es = elements;
+ final int capacity = es.length;
+ // a two-finger algorithm, with hare i reading, tortoise j writing
+ int j = i++;
+ final int end = tail;
+ try {
+ for (;; j = 0) { // j rejoins i on second leg
+ E e;
+ // In this loop, i and j are on the same leg, with i > j
+ for (; i < to; i++)
+ if (!filter.test(e = elementAt(es, i)))
+ es[j++] = e;
+ if (to == end) break;
+ // In this loop, j is on the first leg, i on the second
+ for (i = 0, to = end; i < to && j < capacity; i++)
+ if (!filter.test(e = elementAt(es, i)))
+ es[j++] = e;
+ if (i >= to) {
+ if (j == capacity) j = 0; // "corner" case
+ break;
+ }
+ }
+ return true;
+ } catch (Throwable ex) {
+ // copy remaining elements
+ for (; i != end; i = inc(i, capacity), j = inc(j, capacity))
+ es[j] = es[i];
+ throw ex;
+ } finally {
+ if (end != tail) throw new ConcurrentModificationException();
+ circularClear(es, tail = j, end);
+ // checkInvariants();
}
}
/**
- * 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 o.equals(e).
+ * 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;
- Object x;
- while ( (x = elements[i]) != null) {
- if (o.equals(x))
- return true;
- i = (i + 1) & mask;
+ if (o != null) {
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ if (o.equals(es[i]))
+ return true;
+ if (to == end) break;
+ }
}
return false;
}
@@ -682,15 +1024,15 @@ public class ArrayDeque extends Abstr
/**
* Removes a single instance of the specified element from this deque.
* 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
+ * 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}.
+ *
This method is equivalent to {@link #removeFirstOccurrence(Object)}.
*
* @param o element to be removed from this deque, if present
- * @return true if this deque contained the specified element
+ * @return {@code true} if this deque contained the specified element
*/
public boolean remove(Object o) {
return removeFirstOccurrence(o);
@@ -701,16 +1043,19 @@ public class ArrayDeque extends Abstr
* The deque will be empty after this call returns.
*/
public void clear() {
- int h = head;
- int t = tail;
- if (h != t) { // clear all cells
- head = tail = 0;
- int i = h;
- int mask = elements.length - 1;
- do {
- elements[i] = null;
- i = (i + 1) & mask;
- } while (i != t);
+ circularClear(elements, head, tail);
+ head = tail = 0;
+ // checkInvariants();
+ }
+
+ /**
+ * Nulls out slots starting at array index i, upto index end.
+ */
+ private static void circularClear(Object[] es, int i, int end) {
+ for (int to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ Arrays.fill(es, i, to, null);
+ if (to == end) break;
}
}
@@ -728,7 +1073,24 @@ 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 toArray(Object[].class);
+ }
+
+ private T[] toArray(Class klazz) {
+ final Object[] es = elements;
+ final T[] a;
+ final int size = size(), head = this.head, end;
+ final int len = Math.min(size, es.length - head);
+ if ((end = head + size) >= 0) {
+ a = Arrays.copyOfRange(es, head, end, klazz);
+ } else {
+ // integer overflow!
+ a = Arrays.copyOfRange(es, 0, size, klazz);
+ System.arraycopy(es, head, a, 0, len);
+ }
+ if (tail < head)
+ System.arraycopy(es, 0, a, len, tail);
+ return a;
}
/**
@@ -742,21 +1104,21 @@ public class ArrayDeque extends Abstr
* 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.
+ * {@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 x is a deque known to contain only strings.
+ *
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 String:
+ * allocated array of {@code String}:
*
- *
{@code 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().
+ * 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
@@ -769,12 +1131,16 @@ public class ArrayDeque extends Abstr
*/
@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)
+ final int size;
+ if ((size = size()) > a.length)
+ return toArray((Class) a.getClass());
+ final Object[] es = elements;
+ for (int i = head, j = 0, len = Math.min(size, es.length - i);
+ ; i = 0, len = tail) {
+ System.arraycopy(es, i, a, j, len);
+ if ((j += len) == size) break;
+ }
+ if (size < a.length)
a[size] = null;
return a;
}
@@ -792,21 +1158,19 @@ public class ArrayDeque extends Abstr
ArrayDeque result = (ArrayDeque) super.clone();
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,
+ * @param s the stream
+ * @throws java.io.IOException if an I/O error occurs
+ * @serialData The current size ({@code int}) of the deque,
* followed by all of its elements (each an object reference) in
* first-to-last order.
*/
@@ -818,13 +1182,21 @@ public class ArrayDeque extends Abstr
s.writeInt(size());
// Write out elements in order.
- int mask = elements.length - 1;
- for (int i = head; i != tail; i = (i + 1) & mask)
- s.writeObject(elements[i]);
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ s.writeObject(es[i]);
+ if (to == end) break;
+ }
}
/**
- * Deserialize this deque.
+ * Reconstitutes this deque from a stream (that is, deserializes it).
+ * @param s the stream
+ * @throws ClassNotFoundException if the class of a serialized object
+ * could not be found
+ * @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
@@ -832,12 +1204,32 @@ public class ArrayDeque extends Abstr
// Read in size and allocate array
int size = s.readInt();
- allocateElements(size);
- head = 0;
- tail = size;
+ elements = new Object[size + 1];
+ this.tail = size;
// Read in all elements in the proper order.
for (int i = 0; i < size; i++)
elements[i] = s.readObject();
}
+
+ /** debugging */
+ void checkInvariants() {
+ try {
+ int capacity = elements.length;
+ // assert head >= 0 && head < capacity;
+ // assert tail >= 0 && tail < capacity;
+ // assert capacity > 0;
+ // assert size() < capacity;
+ // assert head == tail || elements[head] != null;
+ // assert elements[tail] == null;
+ // assert head == tail || elements[dec(tail, capacity)] != null;
+ } catch (Throwable t) {
+ System.err.printf("head=%d tail=%d capacity=%d%n",
+ head, tail, elements.length);
+ System.err.printf("elements=%s%n",
+ Arrays.toString(elements));
+ throw t;
+ }
+ }
+
}