Picking elements of a list until condition is met with Java 8 Lambdas

Question

I am trying to switch my mind to think the functional way and recently faced a situation in which I needed to pick up elements from a list until a condition is met and I could not find an easy natural way of achieving this. Obviously I am still learning.

Say I have this list:

List<String> tokens = Arrays.asList("pick me", "Pick me", "pick Me",
    "PICK ME", "pick me and STOP", "pick me", "pick me and Stop", "pick me");

// In a non lambdas was you would do it like below
List<String> myTokens = new ArrayList<>();
for (String token : tokens) {
    myTokens.add(token);
    if (token.toUpperCase().endsWith("STOP")) {
        break;
    }
}

Thank you in advance for your inputs

NOTE: Before publishing this I read Limit a stream by a predicate but I could not see how I can adapt that answer to my problem. Any help would be appreciated thanks.

Answer 1

If you really must use Streams API, keep it simple and use a stream of indexes:

int lastIdx = IntStream.range(0, tokens.size())
        .filter(i -> tokens.get(i).toUpperCase().endsWith("STOP"))
        .findFirst()
        .orElse(-1);

List<String> myTokens = tokens.subList(0, lastIdx + 1);

Or make a new List out of the sublist if you want an independent copy that's not backed by the original list.