New to Java

Hey guys,
I'll post the code, and then the error message below. Essentially I'm getting an error message on the add and it's a bit confusing, since I've imported ArrayList and add is a method in there as well.
My question: What am I missing? If someone could post what I'm missing, I'd appreciate it. No trolls please.

import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.Iterator;

public class CDCollection {
    private ArrayList collection = null;
    private double    totalCost;



    //-----------------------------------------------------------------
    //  Constructor: Creates an initially empty collection.
    //-----------------------------------------------------------------
    public CDCollection() {
        collection = new ArrayList(100);
        totalCost = 0.0;
    }



    //-----------------------------------------------------------------
    //  Adds a CD to the collection, increasing the size of the
    //  collection if necessary.
    //-----------------------------------------------------------------
    public void addCD(String title, String artist, double cost, int tracks) {
        collection.add(new CD(title, artist, cost, tracks));
        totalCost += cost;
    }



    //-----------------------------------------------------------------
    //  Returns a report describing the CD collection.
    //-----------------------------------------------------------------
    public String toString() {
        NumberFormat fmt = NumberFormat.getCurrencyInstance();

        String report = "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
        report += "My CD Collection\n\n";

        report += "Number of CDs: " + collection.size() + "\n";
        report += "Total cost: " + fmt.format(totalCost) + "\n";
        if (collection.size() != 0) {
            report += "Average cost: " + fmt.format(totalCost / collection.size());
        }

        report += "\n\nCD List:\n\n";

        report += CDCollection.createReport(collection);

        return report;
    }



    /**
     *
     * @param al
     * @return
     */
    public static String createReport(ArrayList al) {
        StringBuffer sb = new StringBuffer();
        Iterator iter = al.iterator();

        while (iter.hasNext()) {
            CD aCD = (CD) iter.next();

            sb.append(aCD.toString());
            sb.append(System.getProperty("line.separator"));
        }

        return sb.toString();
    }
} 

and the error message:

CDCollection.java:36: cannot find symbol
symbol: method add(CD)
location: class java.util.ArrayList<java.lang.String>
collection.add(new CD(title, artist, cost, tracks));


Any help would be very appreciated folks.