JOptionPage program to take user input

import javax.swing.*;
import java.util.*;
import java.text.*;

class SectionB{
    static String getMonthName(int m) {
    String month = "invalid";
    DateFormatSymbols dfs = new DateFormatSymbols();
    String[] months = dfs.getMonths();
    if (m >= 0 && m <= 11 ) {
        month = months[m];
    }
    return month;
}

    public static void main(String[] args){
            int days=0;
        String st=JOptionPane.showInputDialog(null,"Enter number between 1 and 12: ");
        int num=Integer.parseInt(st);
        switch(num){
            case 1:
            days=31;
            break;

            case 2:
            String str=JOptionPane.showInputDialog(null,"Is this a leap year?");
            if(str.equalsIgnoreCase("yes")){
            days=29;
            }
            else{
            days=28;
            }
            break;

            case 3: 
            days=31;
            break;

            case 4:
            days=30;
            break;

            case 5: 
            days=31;
            break;

            case 6:
            days=30;
            break;

            case 7: 
            days=31;
            break;

            case 8: 
            days=31;
            break;

            case 9: 
            days=30;
            break;

            case 10:
            days=31;
            break;

            case 11: 
            days=30;
            break;

            case 12: 
            days=31;
            break;

            default:
            System.out.println("Invalid!");
            System.exit(0);
        }
        JOptionPane.showMessageDialog(null,"The Month you entered is "+getMonthName(num-1)+" and it has "+days+" days");
    }
}