ArrayDeque实现Stack的功能

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
    }

 

 

 

评论

1 楼 adam_zs 2013-03-25  

好，谢谢分享。