Why use an ArrayList as a constructor parameter in Java (BlueJ)? -

i'm trying complete assignment in bluej uni , i've hit snag @ first hurdle.

in assignment, given class, names of constructor, methods, , parameters of class. we're not allowed change these because assignments partially marked test unit (or effect).

one of constructors class given as

 public class playlist  {     public playlist(string name, arraylist<track> tracks) {     } 

and have (partially) completed as

public class playlist {    private string listname;    private arraylist<track> listtracks = new arraylist<track>();     /**     * constructs playlist title , arraylist of tracks     *      * @param name name of playlist     * @param tracks arraylist of tracks in playlist     */    public playlist(string name, arraylist<track> tracks) {        listname = name;        //i don't know tracks parameter yet    } 

okay, so, know question (how enter parameters arraylist in bluej?) have create instance of arraylist in order pass parameter in bluej.

what don't understand why - why have used arraylist<track> parameter constructor? benefit of doing this?

(i figure there must benefit doing (if there wasn't functionality wouldn't exist in first place), don't understand what is, , if explain me, i'd appreciative.)

why have used arraylist<track> parameter constructor?

they did allow callers pass arbitrary number of tracks in single parameter.

java offers several options this: pass collection, array, or iterator. if designing signature constructor, prefer collection<track> or @ least list<track> arraylist<track>, in order give callers more options far collection pass constructor.

going array list, should make defensive copy of it. 1 way using collections.copy, this:

collections.copy(this.tracks, tracks); 

once copy complete, should walk through elements of this.track, , ensure not null.