I want understand these code before java lab exam especially methode

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

public class EnglishCalendar
{
public static String[] months = {
"January" , "February" , "March",
"April" , "May" , "June",
"July" , "August" , "September",
"October" , "November" , "December" };
public static int days[] = {
31, 28, 31,
30, 31, 30, 31, 31, 30,
31, 30, 31 };

    private void showMonth(int m, int y) {  
    int lead_spaces = 0;  
      if (m < 0 || m > 11) {  
    System.out.println("It should be 1 to 12");  
        }  
     else {  
         System.out.println();  
         System.out.println("    " + months[m] + " " + y);  
         System.out.println();  
         GregorianCalendar cal = new GregorianCalendar(y, m, 0);  
         System.out.println("Su Mo Tu We Th Fr Sa ");  
         lead_spaces = cal.get(Calendar.DAY_OF_WEEK);  
         int day_of_month = days[m];  
         if (cal.isLeapYear(cal.get(Calendar.YEAR)) && m == 1){ day_of_month++;}  
         for (int i = 0; i < lead_spaces; i++) {  
             System.out.print("   ");  
              }  
         for (int i = 1; i <= day_of_month; i++) {  
            if (i < 10) System.out.print(" ");  
              System.out.print(i);  
            if ((lead_spaces  + i) % 7 == 0) {  
               System.out.println();  
                 }   
               else {
               System.out.print(" ");  
            }  } 
         System.out.println();   }  }  

  private static void doSimpleDateFormat() {  
    Calendar now = Calendar.getInstance();  
    SimpleDateFormat formatter = new SimpleDateFormat("E yyyy.MM.dd 'at' hh:mm:ss a zzz");  
    System.out.print(" \n It is now : " + formatter.format(now.getTime()));  
     System.out.println();  
          }  
    public static void main(String[] args) {  
        String mo = JOptionPane.showInputDialog("Month");  
        String ye = JOptionPane.showInputDialog("Year");  
        int mon = new Integer(mo).intValue();  
        int yea = new Integer(ye).intValue();  
          EnglishCalendar k = new EnglishCalendar();  
              k.showMonth(mon - 1 , yea);  
         doSimpleDateFormat();  

}

}