Question

I’ have very unusual problem with removing elements from List.
Here is my code:

for (int i = 0; i < offers.size(); i++) {
                if(offers.get(i).isSpecialOffer()){
                    offers.remove(i);

                }
        }
  return offers;

When I print out offers for testing, I get the right result everyone is true. But when I try to remove elements with true boolean I get wrong result. It prints out offers with false boolean.
I dont know where is the problem?
Thanks for help

UPDATE:
I have function for removing specialOffers from List. I’ always get some offers with true value.

Answer 1

If you include the remove (which is currently commented out) before you use the System.out.println call, then you’ll be printing out a different value to the one you remove. For example:

Before removal:

0 - Foo
1 - Bar
2 - Baz

Now if i is one, we’ll call remove(1), leaving

0 - Foo
1 - Baz

… so we’ve removed Bar, and then we’d print Baz

You’ll also then not check Baz, as you’d increment i to 2 before testing again.

To do this sort of thing properly, you should either use a loop like this:

for (Iterator<Offer> iterator = offers.iterator(); iterator.hasNext() ;) {
    Offer offer = iterator.next();
    if (offer.isSpecialOffer()) {
        iterator.remove(); // Must remove using the iterator!
        System.out.println(offer.isSpecialOffer() + ".." + offer.getName());
    }
}

Or if you really want to use the index, ideally work backwards to avoid problems:

for (int i = offers.size() - 1; i >= 0; i--) {
    Offer offer = offers.get(i);
    if (offer.isSpecialOffer()) {
        offers.remove(i);
        // Use offer, not offers.get(i)
        System.out.println(offer.isSpecialOffer() + ".." + offer.getName());
    }
}