Why am I getting NotSerializableException?

Question

I have a class implementing Serializable, but I'm having trouble finding why it throws this exception whenever I try to write it it disk. I'm trying to write ValueConatiner.class

public class ValueContainer implements Serializable {
    private static final long serialVersionUID = 2846820178517499793L;
    public String name;
    public MonetaryField buy;
    public MonetaryField sell;
    public MonetaryField revenue;
    public MonetaryField cost;
    public MonetaryField listing_fee;
    public MonetaryField sale_fee;
    public MonetaryField profit;
    public int quantity;
    public int investment;
    public int period;

    public ValueContainer(String n, MonetaryField b, MonetaryField s,
                          MonetaryField r, MonetaryField c, MonetaryField lf,
                          MonetaryField sf, MonetaryField p, int q,
                          int i, int per) {
            name = n;
            buy = b;
            sell = s;
            revenue = r;
            cost = c;
            listing_fee = lf;
            sale_fee = sf;
            profit = p;
            quantity = q;
            investment = i;
            try {
                    period = per;
            } catch(NumberFormatException e) {
                    System.out.println("No data. Enter a number.");
            }
    }
}

I am attempint to write it to disk using this method in a separate class where I hold my JMenuBar.

private void saveFile() {
    if(!currentFile.exists()) {
        loadFile();
    }
    if(currentFile.exists()) {
        try {
            ValueContainer values = getValues();
            FileOutputStream f_out = new FileOutputStream(currentFile);
            ObjectOutputStream obj_out = new ObjectOutputStream(f_out);
            try {
                obj_out.writeObject(values);
            } finally {
                obj_out.close();
                f_out.close();
            }
            System.out.println("Saved!");
        } catch(IOException e) {
            System.out.println(e);
        }
    }
}

Answer 1

I'm just going to take a shot in the dark and say...

MonetaryField needs to be Serializable as well.

Answer 2

Class is serializable if it implements serializable AND all its non-primitive fields are serializable. Probably MonetaryField is not serializable.

Answer 3

...When traversing a graph, an object may be encountered that does not support the Serializable interface. In this case the NotSerializableException will be thrown and will identify the class of the non-serializable object.

Thats from the javadocs. For your Instance to be serializable all objects in the object graph must also be serializable. Double check that this is the case.