Java programming question, please help

Hello. I am taking an Intro to Java class and I'm stuck on a homework question. I was hoping a kind soul could offer some suggestions. Here is the assignment:

Write a program that asks the user to enter a month (1 = January, 2 = February, and so on) and then prints the number of days of the month. For February, print "28 days".

Enter a month (1-12):
5
31 days

Implement a class Month with a method int getDays(). Do not use a separate if or else statement for each month. Use Boolean operators.

I thought it would be cool to have a box pop up and ask the question so that's in my code. I
'm using NetBeans IDE 7.2.1 (Build 201210100934) and Java: 1.7.0; Java HotSpot(TM) 64-Bit Server VM 21.0-b17.

Here is my code:

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package daysinamonth;

import java.util.Scanner;
import javax.swing.JOptionPane;
public class DaysInAMonth {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String month =JOptionPane.showInputDialog("Please enter your month 1-12: ");
double a = Double.valueOf(month);
// int month = in.nextInt();

}

public static void getMonth(double a)
{
if (a == 1 || a == 3 || a == 5 || a ==7 || a ==8 ||a == 10 || a == 12)
{
System.out.println("31");
}
if (a == 4 || a == 6 || a == 9 || a == 11)
{
System.out.println("30");
}
if (a == 2)
{
System.out.println("28");
}
}
}

Any suggestions are much appreciated!