Java 8 Stream to find element in list

Question

I have the following class:

public class Item {
    int id;
    String name;
    // few other fields, contructor, getters and setters
}

I have a list of Items. I want to iterate through the list and find the instance which has a particular id. I'm trying to do it through streams.

public void foobar() {

    List<Item> items = getItemList();
    List<Integer> ids = getIdsToLookup();
    int id, i = ids.size() - 1;

    while (i >= 0) {
        id = ids.get(i);
        Optional<Item> item = items
            .stream()
            .filter(a -> a.getId() == id)
            .findFirst();
        // do stuff
        i--;
    }
}

Is this the best way to iterate over the list and get the element I need? Also, I get an error on the filter line for id which says variables used in lambda expressions must be final or effectively final. Maybe I can define id inside the while loop, that should get rid of the exception. Thanks.

Answer 1

You can try use something like this:

ids.forEach(id -> 
    list.stream()
    .filter(p -> p.getId() == id)
    .findFirst()
    .ifPresent(p -> {
        // do stuff here
    });
);

Optional here shows that your filter method can return a empty stream, so if you call findFirst it can find one or zero elements.