[백준] 10828번 : 스택 - Java(자바)

https://www.acmicpc.net/problem/10828

import java.util.*;
class Stack {
    int size;
    int[] stack;
    
    public Stack(int num){
        stack = new int[num];
        size=0;
    }
    public void push(int num) {
        stack[size] = num;
		size++;
    }
    public int pop() {
		if(size == 0) return -1;
		else {
			int ans = stack[size - 1];
			stack[size - 1] = 0;
			size--;
			return ans;
		}
	}
	public int size() {
		return size;
	}
	public int empty() {
		if(size == 0) return 1;
		else return 0;
	}
	public int top() {
		if(size == 0) return -1;
		else return stack[size - 1];
	}
}
public class Main {
    public static void main(String args[]) {
        Scanner s=new Scanner(System.in);
        StringBuilder sb = new StringBuilder();
        int n=s.nextInt();
        Stack t=new Stack(n);
        
        for(int i=0;i<n;i++) {
			String st = s.next();
			switch (st) {
			case "push":
				t.push(s.nextInt());
				break;
			case "pop":
				sb.append(t.pop()).append('\n');
				break;
			case "size":
				sb.append(t.size()).append('\n');
				break;
			case "empty":
				sb.append(t.empty()).append('\n');
				break;
			case "top":
				sb.append(t.top()).append('\n');
				break;
			}
		}
		System.out.println(sb);
    }
}