java "throws" clause not working

Question

Why does the following code snippet

private void getEvents() throws VersionNotFoundException{
    gameRepository.findAll().forEach(game->{
        HttpHeaders headers = new HttpHeaders();
        String appVersion = getClass().getPackage().getImplementationVersion();
        if (appVersion==null) {
            throw new VersionNotFoundException();
        }
        headers.set("X-TBA-App-Id","4205:"+this.getClass().getPackage().getImplementationVersion());
        HttpEntity<?> requestEntity = new HttpEntity<>(headers);
        restTemplate.exchange(getEventsForYearString, HttpMethod.GET,requestEntity , Event.class, game.getYear());
    });
}

private class VersionNotFoundException extends Exception {
}

in a class cause the line throw new VersionNotFoundException(); to raise a compiler error that VersionNotFoundException must be caught or declared to be thrown? It very clearly is declared to be thrown.

@LewBloch Can you elaborate? The majority of java naming conventions I have seen would consider this compliant. — Trevor Giddings, Mar 21 '17 at 19:41
You have `AppVersion` as a variable name; as such it should begin with a lower-case letter. As spelled it looks like a type name. — Lew Bloch, Mar 21 '17 at 20:03

score 3 · Answer 1 · answered Mar 21 '17 at 05:36

3

The lambda function passed to gameRepository.findAll().forEach() doesn't have throws. That's what the error is saying.

answered Mar 21 '17 at 05:36

kaitoy

1,545
9
16

score 1 · Accepted Answer · answered Mar 21 '17 at 05:41

the lambda method you're overriding doesn't have VersionNotFoundException in its signature, so overridden methods can't either (including your lambda). Since #forEach accepts a consumer which doesn't allow checked exceptions, you always have to catch exceptions in that lambda.

As for determining if you need to throw an exception, I would do that outside of the #forEach entirely:

private void getEvents() throws VersionNotFoundException {
    String appVersion = getClass().getPackage().getImplementationVersion();
    if (appVersion == null) {
        throw new VersionNotFoundException();
    }
    gameRepository.findAll().forEach(game-> {
        HttpHeaders headers = new HttpHeaders();
        headers.set("X-TBA-App-Id", "4205:"+ appVersion);
        HttpEntity<?> requestEntity = new HttpEntity<>(headers);
        restTemplate.exchange(getEventsForYearString, HttpMethod.GET, requestEntity, Event.class, game.getYear());
    });
}

I had forgotten that I was working in a foreach. After I noticed, I ended up changing it to more-or-less what you suggested. — Trevor Giddings, Mar 21 '17 at 06:24

score 0 · Answer 3 · answered Mar 21 '17 at 05:38

0

Checked Exceptions cannot be thrown in lambda expressions. The fact that this was inside a lambda slipped my mind.

answered Mar 21 '17 at 05:38

Trevor Giddings

387
1
4
17

Well they can, the receiving method has to accept a functional interface which allows a checked exception – Rogue Mar 21 '17 at 05:41
@Rogue I had found a stackoverflow answer I that said It couldn't be done. Has that changed since then? http://stackoverflow.com/a/27668305/4160312 – Trevor Giddings Mar 21 '17 at 06:21
You can specify your own functional interfaces, and utilize those for methods. However this isn't wholly stream-compatible – Rogue Mar 21 '17 at 07:16

java "throws" clause not working

3 Answers3