How can I validate two variables with Java 8 Lambda

Question

How can I do this with Java 8 Lambdas:

Optional<String> code;
if (accountType.requiresCode() && (!code.isPresent() || empty(code.get()))) {
    new IllegalArgumentException("Account type " + accountType + " requires code");
}

Optionals can do the job ! http://blog.jhades.org/java-8-how-to-use-optional/ — Digix, Feb 12 '15 at 10:39
And what's the problem with the above code? What would you gain by using lambdas, and where? — JB Nizet, Feb 12 '15 at 10:42
There's no problem with this code. But I wanted to know if I could gain anything by using Lambdas. — Oliveira, Feb 12 '15 at 12:01

score 6 · Accepted Answer · answered Feb 12 '15 at 10:49

You can rewrite the code as

Optional<String> code;
if (accountType.requiresCode()) code.filter(x->!empty(x)).orElseThrow(
  () -> new IllegalArgumentException("Account type " + accountType + " requires code")
);

or, assuming that your empty(code.get()) actually meant code.get().isEmpty():

Optional<String> code=Optional.empty();
if (accountType.requiresCode()) code.filter(x->!x.isEmpty()).orElseThrow(
  () -> new IllegalArgumentException("Account type " + accountType + " requires code")
);

But it doesn’t really add to readability. Lambdas aren’t always better than ordinary code.

I like the `filter` idea, but I think that checking `isPresent()` would be more readable. `if (accountType.requiresCode() && !code.filter(x->!empty(x)).isPresent()) { ... }` — Paolo Fulgoni, Feb 12 '15 at 11:14

score 1 · Answer 2 · answered Feb 12 '15 at 10:46

1

You could use

if (accountType.requiresCode() && code.map(this::empty).orElse(true))

but I'm not sure it makes the code more readable.

answered Feb 12 '15 at 10:46

JB Nizet

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Isn’t this what `Optional.filter` is for? E.g. `code.filter(s -> !empty(s)).isPresent()`; using `map` and `orElse` with `boolean`s feels so wrong… – Holger Feb 12 '15 at 10:54
Using filter is indeed another solution. I just didn't think about it. I agree it's cleaner. But I'm still not sure it makes the code more readable. – JB Nizet Feb 12 '15 at 11:00
I guess, in this case none of these lambda using variants make the code more readable… – Holger Feb 12 '15 at 11:02

score 0 · Answer 3 · edited May 23 '17 at 11:44

0

According to this question Valid usage of Optional type in Java 8 Optional is not a good choice here, though technically possible.

You can rewrite using StringUtils to the much nicer:

final String code = getCodeFromSomething();
if (accountType.requiresCode() && StringUtils.isEmpty(code)) {
    new IllegalArgumentException("Account type " + accountType + " requires code");
}

edited May 23 '17 at 11:44

Community

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1

answered Jan 04 '16 at 16:39

Łukasz Rzeszotarski

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How can I validate two variables with Java 8 Lambda

3 Answers3