在J2SE6引入了ArrayDeque类，它继承了Deque(双向队列)接口，使用此类可以自己实现java.util.Stack类的功能，去掉了java.util.Stack的多线程同步的功能。
例如创建一个存放Integer类型的Stack，只要在类中创建一个ArrayDeque类的变量作为属性，之后定义的出栈、入栈，观察栈顶元素的操作就直接操作ArrayDeque的实例变量即可。
- import java.util.ArrayDeque;
- import java.util.Deque;
-
- public class IntegerStack {
- private Deque<Integer> data = new ArrayDeque<Integer>();
-
- public void push(Integer element) {
- data.addFirst(element);
- }
-
- public Integer pop() {
- return data.removeFirst();
- }
-
- public Integer peek() {
- return data.peekFirst();
- }
-
- public String toString() {
- return data.toString();
- }
-
- public static void main(String[] args) {
- IntegerStack stack = new IntegerStack();
- for (int i = 0; i < 5; i++) {
- stack.push(i);
- }
- System.out.println(stack);
- System.out.println("After pushing 5 elements: " + stack);
- int m = stack.pop();
- System.out.println("Popped element = " + m);
- System.out.println("After popping 1 element : " + stack);
- int n = stack.peek();
- System.out.println("Peeked element = " + n);
- System.out.println("After peeking 1 element : " + stack);
- }
- }
java.util.ArrayDeque的源码：
- private transient E[] elements;
- private transient int head;
- private transient int tail;
-
- /*此处存放e的位置是从elements数组最后的位置开始存储的*/
- public void addFirst(E e) {
- if (e == null)
- throw new NullPointerException();
- elements[head = (head - 1) & (elements.length - 1)] = e;//首次数组容量默认为16，head=（0-1）&(16-1)=15
- if (head == tail)
- doubleCapacity();
- }
-
- /*每次扩容都按插入的先后顺序重新放入一个新的数组中，最新插入的放在数组的第一个位置。*/
- 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 E removeFirst() {
- E x = pollFirst();
- if (x == null)
- throw new NoSuchElementException();
- return x;
- }
-
- public E pollFirst() {
- int h = head;
- E result = elements[h]; // Element is null if deque empty
- if (result == null)
- return null;
- elements[h] = null; // 重新设置数组中的这个位置为null，方便垃圾回收。
- head = (h + 1) & (elements.length - 1);//将head的值回退，相当于将栈的指针又向下移动一格。例如，12--〉13
- return result;
- }
-
- public E peekFirst() {
- return elements[head]; // elements[head] is null if deque empty
- }
以上就是本文的全部内容，希望对大家学习java程序设计有所帮助。 | 
