Question

I was planing on using the writeObject to write my array lists to the internal storage. However, I don’t know how to save/restore more than one of them. Like with SharedPreferences it makes key/value pairs, but with three ArrayLists, how can I save them and then restore them back when needed?

Answer 1

ObjectOutputStream uses a java.io.OutputStream as argument in its constructor. Since FileOutputStream is a derived class of it, you can use it directly. Something like:

String FILENAME = "myfile";
FileOutputStream fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(obj);
oos.close();

Alternatively, if you want to use SharedPreferences instead, you just need a way to serialize the whole ArrayList (perhaps using a ObjectOutputStream to a ByteArrayOutputStream).

A very easy way to do serialize the array (depending on the complexity of the objects stored) is to create a JSONArray to hold the ArrayList values, and use its built-in toString() method.