Java集合ArrayDeque类实例分析

public class ArrayDeque extends AbstractCollection
   implements Deque, Cloneable, Serializable

 /**
  * 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;

 public void addFirst(E e) {
  if (e == null)
   throw new NullPointerException();
  elements[head = (head - 1) & (elements.length - 1)] = e;
  if (head == tail)
   doubleCapacity();
 }

 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;
 }

private boolean delete(int i) {
  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 = ((t - h) & mask))
   throw new ConcurrentModificationException();

  // Optimize for least element motion
  // 为了最小的拷贝数据
  if (front 

 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;
 }