public void saveOnFile() {
    try {
        ObjectOutputStream output = new ObjectOutputStream(new FileOutputStream("object.txt"));
        output.writeObject(mediaList);
        output.close();
    } catch(Exception ex) {
        ex.printStackTrace();
    }
}

    public void readFromFile() {
    try {
        ObjectInputStream inStream = new ObjectInputStream(new FileInputStream("object.txt"));
        this.mediaList.add( (Media) inStream.readObject());
        inStream.close();
    } catch(Exception ex) {
        ex.printStackTrace();
    }
}

java.lang.ClassCastException: java.util.ArrayList cannot be cast to project.Media
at project.MediaHandler.readFromFile(MediaHandler.java:66)
at project.Window.<init>(Window.java:73)
at project.Window.main(Window.java:199)