How to use collect call in Java 8?

Question

Lets say we have this boring piece of code that we all had to use:

ArrayList ids = new ArrayList();
for (MyObj obj : myList){
    ids.add         


        

Answer 1

I use a lot of collector blocks where I create an empty Array and fill it using a loop so I decided I need a utility class of my own not to write the same lines again ad again, here it is:

public class Collections {

    public static  List collect(Set items, Function mapper) {

    return items.stream().map(mapper).collect(Collectors.toCollection(ArrayList::new));
}

}

and use it like this

List prods = Collections.collect(basket.getOrderItems(), OrderItem::getProduct);

or like this

List prods = Collections.collect(basket.getOrderItems(), (item)->item.getProduct().getId());

Though it might look like much more easier to read, it seems streams are a little slower in these kind of scenarios, look here