Is there an equivalent to LINQ's Single in java? Perhaps in lambdaj?
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1Check this one: github.com/nicholas22/jpropel-light, example:new String[] { "james", "john", "john", "eddie" }.where(startsWith("j")).toList().distinct(); – NT_ Oct 08 '11 at 10:27
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jpropel seems nice, but I can't find it in maven repo. too bad ... – Jon Martin Solaas Oct 28 '12 at 12:58
4 Answers
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It's a pretty easy one to implement yourself, to be honest:
public static <T> T single(Iterable<T> source) {
Iterator<T> iterator = source.iterator();
if (!iterator.hasNext()) {
throw new IllegalArgumentException("No elements");
}
T first = iterator.next();
if (iterator.hasNext()) {
throw new IllegalArgumentException("More than one element");
}
return first;
}
(Or put it in a generic class instead of making the method generic. You may decide to use a different exception type, too.)
Jon Skeet
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Still, I prefer @Emil's answer, assuming guava is lightweight enough. With Maven, importing 3rd party libraries is so easy that "integrate a new library" barrier is lowered. See also http://stackoverflow.com/questions/4263607/what-is-the-de-facto-standard-for-action-func-classes – ripper234 Nov 26 '10 at 18:07
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BTW, where were you in the last few days??? I asked about 25 questions in the last few days, some of them are still unanswered, and I'm sure you know the answers to 90% of them :) Almost all of them more important than this question... http://stackoverflow.com/users/11236/ripper234 – ripper234 Nov 26 '10 at 18:12
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@ripper234: Oh Guava is a wonderful library, and if you're happy to use an extra library, it's *absolutely* worth having. And looking at the first couple of pages of your questions, they're database-related ones which I wouldn't know :( – Jon Skeet Nov 26 '10 at 18:27
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Emil
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I was going to look for an example in Guava, but my network connection died :) – Jon Skeet Nov 26 '10 at 17:38
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A less defensive version of @Jon's solution.
Collection<T> coll;
T first = col.iterator().next();
Add checks to taste.
Peter Lawrey
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