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;
    }
}