public class Address
{
    public Address ()
    {
        
    }

    public String identifier ()
    {

    }

    private String _id;
}
public class Address
{
    // return the next unique address
    
    public static synchronized final int getNextAddress ()
    {
        _address++;

        return _address;
    }

    public static int _address = -1;

    private Address ()
    {
    }
}
Update Address.java