Read and Write from File

Question

I am struggling with how to read and write to a file in Java.

I have the following class which will be written to a file:

public class EconAppData implements Serializable {

private static final long serialVersionUID = 1432933606399916716L;
protected transient ArrayList<Favorite> favorites;
protected transient List<CatalogTitle> catalogLists;
protected transient int rangeMonthlySettings;
protected transient int rangeQuarterlySettings;
protected transient int rangeAnnualSettings;

EconAppData() {
    favorites = new ArrayList<Favorite>();
    catalogLists = new ArrayList<CatalogTitle>();
    rangeMonthlySettings = 3;
    rangeQuarterlySettings = 5;
    rangeAnnualSettings = -1;
}
}

This is my read method:

protected Object readData(String filename) {
    Object result;
    FileInputStream fis;
    ObjectInputStream ois;
    try {
        fis = openFileInput(filename);
        ois = new ObjectInputStream(fis);
        result = ois.readObject();
        ois.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        System.err.println(filename + " not found");
        return null;
    } catch (StreamCorruptedException e) {
        e.printStackTrace();
        System.err.println(filename + " input stream corrupted");
        return null;
    } catch (IOException e) {
        e.printStackTrace();
        System.err.println("I/O error in reading " + filename);
        return null;
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
        return null;
    }
    return result;
}

And the write method:

protected Object writeData(String filename, Object data) {
    FileOutputStream fos;
    ObjectOutputStream oos;
    try {
        fos = openFileOutput(filename, Context.MODE_PRIVATE);
        oos = new ObjectOutputStream(fos);
        oos.writeObject(data);
        oos.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        System.err.println(filename + " not found");
    } catch (StreamCorruptedException e) {
        e.printStackTrace();
        System.err.println(filename + " output stream corrupted");
    } catch (IOException e) {
        e.printStackTrace();
        System.err.println("I/O error in writing " + filename);
    }
    return null;
}

The issue : when I am debugging my code, it appears that I am read and writing to my file (so long as the file exists) without hitting any exceptions. I read my data and find that EconAppData is not null, however the ArrayLists are null and the ints are 0. I compute these values and write to the file. I then read the file again (for debugging purposes) and find that all of the data I computed is now gone. Again the EconAppData is not null, however the arraylists are null and the ints are zero.

The question : How do I correctly read and write a class that also contains objects to a file?

Thank you in advance.

Answer 1

Your variables are all transient which means they don't get saved/loaded. Get rid of the transient attributes from all your variables.

See:

Why does Java have transient fields?