package com.smartandroid.sa.aysnc;
import java.util.ArrayDeque;
/**
* �����{@link ArrayDeque}ʵ�֡�
* ���ݾɰ汾Android��{@link ArrayDeque}��������Stack��Queue��
* @author MaTianyu
* 2014-1-31����12:37:26
*/
public class ArrayDequeCompat<E> {
private transient E[] elements;
private transient int head;
private transient int tail;
private static final int MIN_INITIAL_CAPACITY = 8;
// ****** Array allocation and resizing utilities ******
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++;
if (initialCapacity < 0) // Too many elements, must back off
initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
}
elements = (E[]) new Object[initialCapacity];
}
/**
* Double the capacity of this deque. Call only when full, i.e.,
* when head and tail have wrapped around to become equal.
*/
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 = (E[]) a;
head = 0;
tail = n;
}
public ArrayDequeCompat() {
elements = (E[]) new Object[16];
}
public ArrayDequeCompat(int numElements) {
allocateElements(numElements);
}
public void addFirst(E e) {
if (e == null) throw new NullPointerException("e == null");
elements[head = (head - 1) & (elements.length - 1)] = e;
if (head == tail) doubleCapacity();
}
public void addLast(E e) {
if (e == null) throw new NullPointerException("e == null");
elements[tail] = e;
if ((tail = (tail + 1) & (elements.length - 1)) == head) doubleCapacity();
}
public boolean offer(E e) {
return offerLast(e);
}
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
public boolean offerLast(E e) {
addLast(e);
return true;
}
public E poll() {
return pollFirst();
}
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;
}
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;
}
/**
* Returns the number of elements in this deque.
*
* @return the number of elements in this deque
*/
public int size() {
return (tail - head) & (elements.length - 1);
}
}