If/else statements in for loops (java)

I need help with an error I'm getting while using if/else statements in a for loop.

This is my code up until now:

public class DD {  
public static void main(String[] args) {
     String[] name = {"naima", "rayan", "zakaria", "aliya", "hammad"};
     String[] day = {"9", "23", "11", "21", "19"};
     String[] month = {"3", "11", "6", "5", "7"};
     String[] year = {"2021", "2021", "2021", "2021", "2021"};
     

    System.out.println("Upcoming bookings: ");
    for (int i = 0; i < day.length; i++) {
        if (day[i] >= 21) {
       System.out.println("Customer name: " + name[i]);
       System.out.println("Date of booking: " + day[i] + "/" + month[i] + "/" + year[i]);
       System.out.println("Number of People: " + "-");
    }
        else {
            System.out.println("No bookings");
        }
    }
}
}

It is giving an error beside the if statement however there is no detail as to what the error is. Any help regarding the issue would be much appreciated.