栈的模拟

特点：先进后出，也就是比队列要更简单，用一个索引就ok了，栈的打印也是按照其特点来打印的。

package a;

import java.util.Scanner;

public class StaDemo {
    public static void main(String[] args) {
        Sta sta = new Sta(2);
         String word ="";
         boolean flag = true;
        Scanner scanner = new Scanner(System.in);
        while (flag) {
            System.out.println("show show the data");
            System.out.println("push add data");
            System.out.println("pop get data");
            System.out.println("exit  return");
            word = scanner.next();
            switch (word) {
                case "show":sta.show();
                break;
                case "push":
                    System.out.println("please put");
                    sta.push(scanner.nextInt());
                    break;
                case "pop":
                    int pop = 0;
                    try {
                        pop = sta.pop();
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    System.out.println("pop = " + pop);
                    break;
                case "exit":scanner.close();
                flag = false;
                break;
                default: break;



            }
        }
        System.out.println("have exit");

    }
}

class Sta{
    int top;
    int max;
    int [] arr;

    public Sta(int max) {
        this.max = max;
        arr = new int[max];
        top = -1;
    }

    public boolean isFull() {
        return (max-1)==top;
    }

    public boolean isEmpty() {
        return top == -1;
    }

    public void push(int val) {
        if (isFull()) {
            System.out.println("isFull");
            return;
        }
        top++;//这是先找位置，然后赋值
        arr[top]=val;
    }

    public int pop() {
        if (isEmpty()) {
            throw new RuntimeException("isEmpty");
        }
        int res = arr[top];
        top--;
        return res;
    }

    public void show() {
        if (isEmpty()) {
            System.out.println("isEmpty");
            return;
        }
        for (int i = top; i >=0 ; i--) {
            System.out.println(arr[i]);

        }
    }
}