异常可以引发相同的异常吗？

Question

Sorry if this could be a stupid question but i'm learning Java and i'm experiencing some problems with exceptions. I have this code of my first project:

protected void makePurchase(int userId, Product item, int quantity) throws ItemNotBuyableException {        
    int id = item.getId();
    int count = 0;
    boolean flag = true;

    for (int i=0; i < quantity; i++) {
        try {
            catalog.sellProduct(id);
            count++;
        }
        catch (ItemNotBuyableException e) {
            flag = false;
        }
    }

    orders.addOrder(new Purchase(new GregorianCalendar(), id, item, item.getPrice(), count, userId));

    if (!flag)
        throw new ItemNotBuyableException();
}

Is it legit?

Answer 1

Yes it is legitimate.

Theoretically, you can catch it, do some more stuff that only your class knows how to do, then throw it to whoever is using you.

try {
    catalog.sellProduct(id);
    count++;
}
catch (ItemNotBuyableException e) {
    doMoreStuff();
    //Better let other callers know so they can handle it appropriately
    throw e;
}

Answer 2

This is better:

protected void makePurchase(int userId, Product item, int quantity) throws ItemNotBuyableException {
    int id = item.getId();
    int count = 0;

    boolean flag = true;
    for (int i = 0; i < quantity; i++) {

        if(!catalog.sellProduct(id)) {
            flag = false;
            continue;
        }
        count++;
    }

    orders.addOrder(new Purchase(new GregorianCalendar(), id, item, item.getPrice(), count, userId));

    if (!flag)
        throw new ItemNotBuyableException();
}