Why do I receive this warning when working with an ArrayList?

Question

The warning I receive...
Note: C:\Documents and Settings\Owner\.netbeans\4.1\Cis320\Lab6\src\scanPorts.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
The code it is reffering to...
            //fill the ArrayList with ports to be scanned
            int totalPorts = LAST_PORT - FIRST_PORT + 1;
            ArrayList ports = new ArrayList(totalPorts);
            for(int i = FIRST_PORT; i <= LAST_PORT; i++){
                PortInfo current = new PortInfo(i);
                ports.add(current);
            }

Answer 1

Yup, that is exactly what it is telling me. Thanx for the reply.
Generics are new to me, I found documentation on generics at...
http://java.sun.com/developer/technicalArticles/releases/j2se15langfeat/
My code now looks like...
            //fill the ArrayList with ports to be scanned
            int totalPorts = LAST_PORT - FIRST_PORT + 1;
            ArrayList<PortInfo> ports = new ArrayList<PortInfo>(totalPorts);
            for(int i = FIRST_PORT; i <= LAST_PORT; i++){
                PortInfo current = new PortInfo(i);
                ports.add(current);
            //the <PortInfo> is known as a generic
            //Generics, which are also known as parameterized types, provide
            //compile-time typesafety for collections and eliminate the drudgery
            //of casting.
            //Generics enable more compile-time type checking and therefore
            //mismatch errors are caught at compile time rather than at runtime.
            //So if I try to add a String to this ArrayList anywhere in this
            //code, the compiler will scream instead of me during runtime.