Error while reading an ArrayList of Objects from a file?

Question

I have an array of Objects stored in "rootFile". I would like to read back the objects into another ArrayList. So far I tried this:

List<NoteCard> cardArray = new ArrayList<>();

try {
    FileInputStream fis = openFileInput(rootFile);
    ObjectInputStream ois = new ObjectInputStream(fis);
    cardArray = (List<NoteCard>)ois.readObject();
    ois.close();
    fis.close();
} catch(FileNotFoundException e) {
    e.printStackTrace();
} catch(IOException e) {
    e.printStackTrace();
} catch(ClassNotFoundException e) {
    e.printStackTrace();
}

"Unchecked cast" is a warning, not an exception, error or compile time error. So, what is your actual question/issue? — Tom
– Tom, Commented Feb 3, 2018 at 3:36
You are right. It was running but I wasn't able to read anything from the list and I thought "unchecked cast" was causing it. — D.H.
– D.H., Commented Feb 3, 2018 at 3:43
"I wasn't able to read anything from the list", so your issue isn't even related to "reading from file" and the issue was that you just don't know how to handle the List interface? In that case the answer below can correct your issue there, but mind that it is completely wrong in regard of serialization. The suggested changes wouldn't fix serialization issues. — Tom
– Tom, Commented Feb 3, 2018 at 3:45

Avijit Karmakar · Accepted Answer · 2018-02-03 04:38:31Z

1

You can remove the unchecked cast by doing this:

ArrayList<NoteCard> cardArray = new ArrayList<>();

try {
    FileInputStream fis = openFileInput(rootFile);
    ObjectInputStream ois = new ObjectInputStream(fis);
    Object object = ois.readObject();
    if (object instanceof ArrayList) {
        ArrayList arrayList = (ArrayList) object;
        for (Object object : arrayList) {
            cardArray.add((NoteCard) object);
        }
    }
    ois.close();
    fis.close();
} catch(FileNotFoundException e) {
    e.printStackTrace();
} catch(IOException e) {
    e.printStackTrace();
} catch(ClassNotFoundException e) {
    e.printStackTrace();
}

edited Feb 3, 2018 at 4:38

answered Feb 3, 2018 at 3:19

Avijit Karmakar

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3 Comments

D.H. Over a year ago

Ahh ok. Do I also change: cardArray = (List<NoteCard>)ois.readObject(); to cardArray = (ArrayListt<NoteCard>)ois.readObject(); ?

Avijit Karmakar Over a year ago

Yes. You have to change that.

Tom Over a year ago

I'd like to point out that your information regarding "List is not Serializable" are wrong. It is correct that the interface (or the parent interfaces) isn't serializable itself, but that doesn't matter, since the referred object is and that's the only thing that matters. (for the collection, NoteCard must be serializable as well, obviously)

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