TrackDAO: what can be improved?

public class TrackDAO {
private List tracks;
private Connection con;

public TrackDAO() {
    tracks = new LinkedList();
}

public void addTrack(Track track){
    tracks.add(track);
}

public void connect() throws Exception{
    con = Database.getInstance().connect();
}

public void disconnect() {
    Database.getInstance().disconnect();
}

public void saveToFile(File file) throws IOException {
    File getFile = file;
    if (Utils.getExtension(getFile) == null){
        String url = getFile.getAbsolutePath();
        url += "." + Utils.ml;
        getFile = new File(url);
    }

    FileOutputStream fos = new FileOutputStream(getFile);
    ObjectOutputStream oos = new ObjectOutputStream(fos);

    Track[] trackArray = tracks.toArray(new Track[tracks.size()]);
    oos.writeObject(trackArray);
    oos.close();
}

public void loadFromFile(File file) throws IOException {
    FileInputStream fis = new FileInputStream(file);
    ObjectInputStream ois = new ObjectInputStream(fis);
    try {
        Track[] trackArray = (Track[])ois.readObject();
        tracks.clear();
        tracks.addAll(Arrays.asList(trackArray));
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
    ois.close();
}

• first of all, your DAO class is not thread safe. Are you sure this behavior is the goal?

• connect() method creates a connection every time when it is called, and doesn't disconnect the previous one, this could cause a memory leak

• at the same method throwing Exception is in order to avoid

• at saveToFile() why do you need a new pointer to the file object? It's code smell, and the original file is not declared as final so you should replace it anytime

• String url = getFile.getAbsolutePath();url += "." + Utils.ml; should be replace with String url getFile.getAbsolutePath() + "." + Utils.ml; It compiles to StringBuilder, so it's a cheaper operation then the 2 line version.

• at Track[] trackArray = tracks.toArray(new Track[tracks.size()]); you don't need to initialize the new array with the same size, 0 also will be ok

• instead of manually close resource(s) in Java 7 you should use an AutoCloseable with try

• loadFromFile() is not so nice. For me it's annoying that loadFromFile() drops all of my Tracks previously! This is strange, and need to know this behavior to use this class. If you want to write clean code, you have to avoid things like that.

• e.printStackTrace() is not acceptable in business applications, so if this is a hobby/school project it could be ok, otherwise it's a big mistake.

• loadData() -> tracks.clear() -> same story

• This class is not a clean DAO, it's a mixed something, because it not just representing Data Access, it contains other logic, and holding data. I suggest to split the class, create a thread safe stateless data access object, and a container which handles the current Tracks. In this way you should create arbitary number of containers, so you don't need to clear the tracks for example

• at saveToDatabase() check existing should be a separate method

• those Strings are code smell

• the if else contains code duplication, you do almost the same on different statements with the same class

• checkStatement.close() always close as soon as possible

• missing error handler, if some error occurs the statements stay open

• deleteTrack() code duplication!

• checkStatement.close() close ASAP