How to prints keys in a hashmap.

<pre>public class MapTester
{
    // instance variables - replace the example below with your own
    private HashMap<String, String> contacts;

    /**
     * Constructor for objects of class MapTester
     */
    public MapTester()
    {
        contacts = new HashMap<String, String>();

    }

    /**
     * Enter the given pair into the HashMap.
     * @param name A contact name (the key).
     * @param number The contact's phone number (as a string) (the value).
     */
    public void enterNumber(String name, String number)
    {
        contacts.put(name, number);
    }

    /**
     * Look up the given name in the map and return the associated number.
     * @param name The name to be looked up (the key)
     * @return The assoicated number, if any (the value).
     */
    public String lookUpNumber(String name)
    {
        return contacts.get(name);
    }

    /**
     * Print out the names (keys) in the map, one per line.
     */
    public void listNames()
    {
        for(String name: contact){
            System.out.println(contacts.keySet());
        }
    }
}