Java IP Address Program - Check If It Is Public Or Private

I am doing an assignment for a college class. We are asked to get user input and decide if it is a valid IP address and then check what class the address is and if it is a public or private address.

So far, I can get the input, and check to see if the numbers are in a valid range. I can also display the IP address to the user. I am having an issue figuring out how to get the program to check the classes and whether they are public or private.

import javax.swing.JOptionPane;
/**
This program will take user input and calculate whether it is a valid IP address and the class that it belongs to.
*/

public class shortONE_1
{
public static void main(String[] args)
{
//Variables
final int MIN_OC = 1; //Minimum number accepted
final int MAX_OC = 255; //Maximum number accepted
final int MIN_A = 1; //Min number for class A
final int MAX_A = 127; //Max number for class A

[Code] ....