Stack Practice in java

Today practiced the Stack in java and try the problem to check the balanced brackets
here's is an code :

import java.util.Scanner;
import java.util.Stack;
import java.util.StringTokenizer;

public class brackets {
static boolean isvalid(String s){

    Stack<Character> stack=new Stack<>();    for (char i:s.toCharArray()){        if(i =='{' || i=='['){            stack.push(i);        }        else {            if (stack.isEmpty()) {                return false;            }            char top = stack.pop();            if (i == '}' && top != '{' || i == ']' && top != '[') {                return false;            }        }    }    return stack.isEmpty();}public static void main(String[] args) {    Scanner in=new Scanner(System.in);    System.out.println("Enter the string :");    String s= in.nextLine();    System.out.println(isvalid(s));}

}