java栈的实现

可以采用数组与链表两种方法来实现栈。

　1、用数组实现栈

 import java.util.Arrays;
 public class MyStack<E>{
     private Object[] stack;
     private int size; //数组中存储元素的个数
     public MyStack(){
         stack = new Object[10]; //初始化长度为10
     }
     //判断堆栈是否为空
     public boolean isEmpty(){
         return size == 0;
     }

     public E peek(){
         if(isEmpty()){
             return null;
         }
         return(E) stack[size-1];
     }

     public E pop(){
         E e = peek();
         stack[size-1] = null;
         size--;
         return e;
     }

     public E push(E item){
         ensureCapacity(size+1);
         stack[size++] = item;
         return item;
     }

     //判断数组是否已满，若已满，则扩充数组空间
     private void ensureCapacity(int size){
         int len = stack.length;
         if(size > len){//数组已满
             int newLen = 10;//每次数组扩充的容量
             stack = Arrays.copyOf(stack,newLen);
         }
     }
 }

　2、用链表实现栈

 class Node{
     Node next = null;
     int data;
     public Node(int data){this.data = data;}
 }

 public class Stack<E>{
     Node<E> top = null;

     public boolean isEmpty(){
         return top == null;
     }

     public void push(E data){
         Node<E> newNode = new Node<E>(data);
         newNode.next = top;
         top = newNode;
     }

     public E pop(){
         if(this.isEmpty())
             return null;
         E data = top.data;
         top = top.next;
         return data;
     }

     public E peek(){
         if(isEmpty()){
             return null;
         }
         return top.data;
     }
 }