在J2SE6引入了ArrayDeque類，它繼承了Deque(雙向隊列)接口，使用此類可以自己實現(xiàn)java.util.Stack類的功能，去掉了java.util.Stack的多線程同步的功能。
例如創(chuàng)建一個存放Integer類型的Stack，只要在類中創(chuàng)建一個ArrayDeque類的變量作為屬性，之后定義的出棧、入棧，觀察棧頂元素的操作就直接操作ArrayDeque的實例變量即可。
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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的源碼：
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private transient E[] elements; private transient int head; private transient int tail; /*此處存放e的位置是從elements數(shù)組最后的位置開始存儲的*/ public void addFirst(E e) { if (e == null) throw new NullPointerException(); elements[head = (head - 1) & (elements.length - 1)] = e;//首次數(shù)組容量默認(rèn)為16，head=（0-1）&(16-1)=15 if (head == tail) doubleCapacity(); } /*每次擴(kuò)容都按插入的先后順序重新放入一個新的數(shù)組中，最新插入的放在數(shù)組的第一個位置。*/ 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; // 重新設(shè)置數(shù)組中的這個位置為null，方便垃圾回收。 head = (h + 1) & (elements.length - 1);//將head的值回退，相當(dāng)于將棧的指針又向下移動一格。例如，12--〉13 return result; } public E peekFirst() { return elements[head]; // elements[head] is null if deque empty } |
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