I am a student doing my final project, I need help urgently. Can anyone please advise me?

I am not sure how I can apply write and read for a collection. I have written it out to a File through an ObjectOutputStream objectOut with objectOut.writeObject(arraylist[i]). That seems to work and the file is there. When I attempt to read it back with arraylist = in.readObject(),I can't get anything. Actually I need to save all my objects into a file then retrieve it back later by doing so.

I am not sure am I doing the correct way? or anyone please advise me for a better way?

Thanks for any guidance here.