哈哈，大家平时都有使用过浏览器吧，是不是经常使用浏览器的后退功能呢？
每一次后退，浏览器都会回到上一个浏览的网页。大家有没有想过这个后退操作的基本原理呢？
没错，就是用到了栈这个数据结构。
注意点：栈一定是线性表，但是线性表却不一定是栈。从数据结构上，都是一组数据，按照有序的形式排列起来，但是线性表和栈对数据的操作是不相同的。
下面给出一个栈的接口定义
package net.itaem.list;
/**
* 栈的接口定义
* @author luohong QQ 846705189
* */
public interface Stack<T> {
/**
* 判断一个栈是否为空
* @return 如果为空，返回true；否则，返回false
* */
public boolean isEmpty();
/**
* 压入栈一个元素
* @param e 即将要压入栈的元素
* */
public void push(T e);
/**
* 弹出一个栈顶元素，并且删除该元素
* @return 返回栈顶元素
* */
public T pop();
/**
* 返回栈元素长度大小
* @return 栈元素长度大小
* */
public int size();
/**
* 获得栈顶元素，但是不删除该元素
* @return 返回栈顶元素
* */
public T getTop();
/**
* 将栈清空
* */
public void clear();
}
下面采用数组来实现一个栈，使用数组最大的缺点就是，堆栈所能容纳的元素数量是有限个的，不能动态性增长（当然，可以通过编程实现）
package net.itaem.list.impl;
import net.itaem.list.Stack;
/**
* 使用数组来实现的栈
*
* @author luohong QQ 846705189
* */
public class ArrayStack<T> implements Stack<T> {
//使用数组来实现，注意：使用了Object数组来实现而不是T[]...因为T[]是错误的，具体内容可以参考泛型的知识
private Object[] elements;
//使用top指定来标识栈顶，默认为-1，代表栈为空
private int top = -1;
//栈的元素长度
private int size;
//栈的数组长度，目前这个栈是简单的，一旦初始化后，长度不可以修改
private int length;
/**
* 初始化栈，默认长度为10
* */
public ArrayStack(){
this.length = 10;
elements = new Object[10];
}
/**
* 初始化栈，指定栈的长度
* */
public ArrayStack(int length){
this.length = length;
elements = new Object[length];
}
@Override
public boolean isEmpty() {
return top == -1;
}
@Override
public void push(T e) {
//元素大小加1
size++;
//栈顶网上移动一个
top++;
if(size > length) throw new RuntimeException("栈已满");
//保存元素
elements[top] = e;
}
@SuppressWarnings("unchecked")
@Override
public T pop() {
T result = null;
if(top >= 0){
result = (T)elements[top];
elements[top] = null; //防止造成内存泄露
size--;
top--;
}
else throw new RuntimeException("栈已经为空");
return result;
}
@Override
public int size() {
return size;
}
@SuppressWarnings("unchecked")
@Override
public T getTop() {
T result = null;
if(top != -1) {
result = (T)elements[top];
}
return result;
}
@Override
public void clear() {
//清空所有的栈内元素
while(top >= 0){
for(int i=0; i<size; i++){
elements[i] = null;
}
}
}
public String toString(){
StringBuilder sb = new StringBuilder();
if(top == -1) sb.append("null");
else{
for(int i=0; i<size; i++){
sb.append(elements[i] + " ");
}
}
return "the array stack size is " + size + " and the elements is " + sb.toString();
}
public static void main(String[] args) {
Stack<Integer> arrayStack = new ArrayStack<Integer>(10);
for(int i=0; i<10; i++){
arrayStack.push(i);
}
//如果执行这一句，就会报错
//arrayStack.push(10);
System.out.println(arrayStack);
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println("top element value is " + arrayStack.getTop());
System.out.println("is empty ? " + arrayStack.isEmpty());
System.out.println(arrayStack);
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println(arrayStack.pop());
System.out.println("is empty ? " + arrayStack.isEmpty());
}
}
输出结果
the array stack size is 10 and the elements is 0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 top element value is 4 is empty ? false the array stack size is 5 and the elements is 0 1 2 3 4 4 3 2 1 0 is empty ? true
哈哈，是不是很简单呢？不过不要忽视堆栈的作用哦，这也是我们经常会使用到的数据结构呢。
下面使用节点来实现堆栈，也叫做链栈，接口不变，只是内部实现改用节点类来实现。这种堆栈的优点是，没有长度限制， 可以自由添加
package net.itaem.list.impl;
import net.itaem.list.Stack;
public class LinkedStack<T> implements Stack<T> {
/**
* 定义一个类来模拟节点
* */
private class Node<E>{
//节点数据
private E data;
//该节点的下一个节点
private Node<E> next;
/**
* 初始化节点
* */
public Node(E data, Node<E> next){
this.data = data;
this.next = next;
}
public E data(){
return data;
}
public Node<E> next(){
return next;
}
public void setNext(Node<E> next){
this.next = next;
}
public void setData(E data){
this.data = data;
}
}
//定义一个栈顶节点
private Node<T> top;
//保存栈的元素个数
private int size;
/**
* 初始化一个空的栈
* */
public LinkedStack(){
}
@Override
public boolean isEmpty() {
return top == null;
}
@Override
public void push(T e) {
//压入一个新的节点元素
Node<T> newNode = new Node<T>(e, top);
top = newNode; //将栈顶元素移动
//元素长度加1
size++;
}
@Override
public T pop() {
T result = null;
Node<T> free = top;
//这时候要将这个应用删除掉，防止内容无意识溢出
if(top != null){
result = top.data();
top = top.next();
//释放应用的的节点元素
free = null;
}else{
throw new RuntimeException("栈已经为空");
}
//元素长度减一
size--;
return result;
}
@Override
public int size() {
return size;
}
@Override
public T getTop() {
if(top != null) return top.data();
else return null;
}
@Override
public void clear() {
Node<T> p = top;
while(p != null){
p.setData(null); //释放节点
Node<T> q = p;
p = p.next();
q.setNext(null);
}
size = 0;
top = null;
}
@Override
public String toString(){
StringBuilder sb = new StringBuilder();
if(size == 0) sb.append("null");
else{
Node<T> p = top;
//遍历所有节点元素
while(p != null){
sb.append(p.data() + " ");
p = p.next();
}
}
return "the stack size is " + size + " and the elements is " + sb.toString();
}
public static void main(String[] args) {
LinkedStack<Integer> linkedStack = new LinkedStack<Integer>();
for(int i=0; i<10; i++){
linkedStack.push(i);
}
System.out.println("before pop\n" + linkedStack);
System.out.println(linkedStack.pop());
System.out.println(linkedStack.pop());
System.out.println(linkedStack.pop());
System.out.println(linkedStack.pop());
System.out.println(linkedStack.pop());
System.out.println(linkedStack.pop());
System.out.println("after pop\n" + linkedStack);
linkedStack.clear();
System.out.println("after clear\n" + linkedStack);
}
}
before pop the stack size is 10 and the elements is 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 after pop the stack size is 4 and the elements is 3 2 1 0 after clear the stack size is 0 and the elements is null
总结：堆栈，不过是一种特殊的线性表，它的操作更加简单。
下面给出java.util.Stack
/*
* %W% %E%
*
* Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util;
/**
* The <code>Stack</code> class represents a last-in-first-out
* (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
* operations that allow a vector to be treated as a stack. The usual
* <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
* method to <tt>peek</tt> at the top item on the stack, a method to test
* for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
* the stack for an item and discover how far it is from the top.
* <p>
* When a stack is first created, it contains no items.
*
* <p>A more complete and consistent set of LIFO stack operations is
* provided by the {@link Deque} interface and its implementations, which
* should be used in preference to this class. For example:
* <pre> {@code
* Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
*
* @author Jonathan Payne
* @version %I%, %G%
* @since JDK1.0
*/
public
class Stack<E> extends Vector<E> {
/**
* Creates an empty Stack.
*/
public Stack() {
}
/**
* Pushes an item onto the top of this stack. This has exactly
* the same effect as:
* <blockquote><pre>
* addElement(item)</pre></blockquote>
*
* @param item the item to be pushed onto this stack.
* @return the <code>item</code> argument.
* @see java.util.Vector#addElement
*/
public E push(E item) {
addElement(item);
return item;
}
/**
* Removes the object at the top of this stack and returns that
* object as the value of this function.
*
* @return The object at the top of this stack (the last item
* of the <tt>Vector</tt> object).
* @exception EmptyStackException if this stack is empty.
*/
public synchronized E pop() {
E obj;
int len = size();
obj = peek();
removeElementAt(len - 1);
return obj;
}
/**
* Looks at the object at the top of this stack without removing it
* from the stack.
*
* @return the object at the top of this stack (the last item
* of the <tt>Vector</tt> object).
* @exception EmptyStackException if this stack is empty.
*/
public synchronized E peek() {
int len = size();
if (len == 0)
throw new EmptyStackException();
return elementAt(len - 1);
}
/**
* Tests if this stack is empty.
*
* @return <code>true</code> if and only if this stack contains
* no items; <code>false</code> otherwise.
*/
public boolean empty() {
return size() == 0;
}
/**
* Returns the 1-based position where an object is on this stack.
* If the object <tt>o</tt> occurs as an item in this stack, this
* method returns the distance from the top of the stack of the
* occurrence nearest the top of the stack; the topmost item on the
* stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
* method is used to compare <tt>o</tt> to the
* items in this stack.
*
* @param o the desired object.
* @return the 1-based position from the top of the stack where
* the object is located; the return value <code>-1</code>
* indicates that the object is not on the stack.
*/
public synchronized int search(Object o) {
int i = lastIndexOf(o);
if (i >= 0) {
return size() - i;
}
return -1;
}
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = 1224463164541339165L;
}
原文地址：http://blog.csdn.net/u010469003/article/details/24627971
