1. 栈 (stack)

栈满足“先进后出”，换句话说就是“后进先出”。

图片来自网络，侵删

用数组模拟一个栈实现如下：

package com.stackAndQueue;

public class myStack {
    private int[] elem;

    public myStack(){
        int[] elem = new int[0];
    }

    /**
     * 向栈顶压入元素。和可变数组中添加元素的方法完全一样
     * @param n 被压入的元素
     * */
    public void push(int n){
        int[] newArr = new int[elem.length + 1];
        newArr[elem.length] = n;
        for (int i = 0; i < elem.length; i++){
            newArr[i] = elem[i];
        }
        elem = newArr;
    }

    /**
     * 取出栈顶元素
     * @return 被取出栈顶元素
     * */
    public int pop(){
        if (this.isEmpty()){
            throw new RuntimeException("The stack is empty.");
        }
        int ele = elem[elem.length - 1];
        int[] newArr = new int[elem.length - 1];
        for (int i = 0; i < newArr.length; i++){
            newArr[i] = elem[i];
        }
        elem = newArr;
        return ele;
    }

    /**
     * 查看栈顶元素
     * @return 栈顶元素
     * */
    public int peek(){
        if(this.isEmpty()){
            throw new RuntimeException("The stack is empty!");
        }
        return elem[elem.length - 1];
    }

    /**
     * 检查列表是否为空？
     * */
    public boolean isEmpty(){
        return (elem.length == 0);
    }
}

2. 队列 (Queue)

队列则是“先进先出”。

图片来自网络，侵删

用数组模拟一个队列如下：

package com.stackAndQueue;

public class MyQueue {
    private int[] queue;

    public MyQueue(){
        int[] queue = new int[0];
    }

    /**
     * 入队
     * @param n 入队的元素
     * */
    public void offer(int n){
        int[] tmp = new int[queue.length + 1];
        tmp[queue.length] = n;
        for(int i = 0; i < queue.length; ++i){
            tmp[i] = queue[i];
        }
        queue = tmp;
    }

    /**
     * 出队
     * @return 要出队的元素
     * */
    public int poll(){
        if (this.isEmpty())
            throw new RuntimeException("The queue is empty!");
        int res = queue[0];
        int[] tmp = new int[queue.length - 1];
        for (int i = 0; i < tmp.length; ++i){
            tmp[i] = queue[i + 1];
        }
        queue = tmp;
        return res;
    }

    /**
     * 判断队列是否为空
     * @return true or false
     * */
    public boolean isEmpty(){
        return queue.length == 0;
    }
}