题解 | #【模板】栈#

import java.util.Scanner;
import java.util.Stack;
public class Main{
    public static void main(String[] args){
        int line;
        Stack stack = new Stack<Integer>();
        Scanner sc = new Scanner(System.in);
        line = sc.nextInt();
        String text;
        String[] Arr;
        int i=0;
        for(i=0;i<line;i++){
            text = sc.nextLine();
            if(text.equals("")){
                i--;
                continue;
            }
            String sub = text.substring(0,3);
            if(sub.equals("pop")){
                if(stack.isEmpty())
                    System.out.println("error");
                else
                    System.out.println(stack.pop());
            }else if(sub.equals("top")){
                if(stack.isEmpty())
                    System.out.println("error");
                else
                    System.out.println(stack.peek());
            }else if(sub.equals("pus")){
                stack.push(text.substring(5));
            }
        }
    }
}

需要注意的是：
1.要考虑输入为空字符串的情况，即判断是否为""，" "表示内容为空格的字符串 2.Stack中方法peek(),push(),pop(),empty()