How can I find an element whether it exists in a List or not using Google Guava?

Question

I have a List<String> I need to find whether the particular string exists inside a List or not.

for Eg:

String str = "apple";

List<String> listObject = Lists.newArrayList("apple", "orange", "banana");

I need to find whether str exists in listObject or not using Google Guava.

So I need a true or false result.

How can I achieve this?

Why do you want `Guava` for this? – Keppil Jan 30 '14 at 13:10 — Keppil, Jan 30 '14 at 13:10

score 18 · Answer 1 · answered Jan 30 '14 at 13:10

18

This is a standard part of the Java Collections API:

boolean exists = listObject.contains(str);

answered Jan 30 '14 at 13:10

Stewart

I think I misunderstood the question. – Stewart Jan 30 '14 at 18:05
1

I don't think you did. – ColinD Jan 30 '14 at 19:53
The question was specifically asking how to do it using Guava, and I missed that point. `FluentIterable.contains()` calls `Iterables.contains()` which logic is different, including suppressing `NullPointerException` – Stewart Jan 31 '14 at 04:25
1

Yeah, the thing is that there is no good reason to want to do this _using Guava_ when the way one _should_ do this (as you pointed out) exists in the standard APIs. And the behavior of throwing `NPE` from `Collection.contains(null)` is rare enough (I'm not sure I know of any implementations that actually do that) that no one should be using `FluentIterable.contains` _just_ for that unless they know it's something they need to worry about. And `ArrayList` doesn't do that anyway. – ColinD Jan 31 '14 at 17:04

score 4 · Accepted Answer · answered Jan 30 '14 at 13:24

4

I'm agree that this can be done (and should, maybe) with the standard Collections API, but anyway, in Guava you can do it like this:

List<String> strList = Arrays.asList(new String[] {"one", "two", "3", "4"});
boolean exists = FluentIterable.from(strList).contains("two");

answered Jan 30 '14 at 13:24

yamilmedina

8

You could even replace `.contains("two")` by `.anyMatch(Predicates.equalTo("two"))` for a bit more obfuscation. – Frank Pavageau Jan 30 '14 at 13:31
The main difference between this solution and the Collections API is that this solution works on any `Iterable`. In other words, the `Arrays.asList()` part is redundant. Just pass the array straight in. – Stewart Jan 30 '14 at 18:08
1

@Stewart: Arrays are not `Iterable`, unfortunately. Plus, you can write `Arrays.asList(array).contains("two")` if all you need is the contains check. – ColinD Jan 31 '14 at 17:06
Dah! Shorthand `for` loop strikes again! http://stackoverflow.com/questions/1160081/why-is-an-array-not-assignable-to-iterable – Stewart Jan 31 '14 at 17:15

2 Answers2