Cleanest way to find objects matching certain criteria in a java.util.List?

Question

I could write myself a helper class that does this when given a functor, but I was wondering if there's a better approach, or if there's something already in the standard library (seems like there should be).

Answers I've found on StackOverflow are all for C# which doesn't help me.

Thanks

Answer 1

No - there isn't. Apache commons-collections has predicates for this sort of thing but the resultant code (using anonymous inner classes) is usually ugly and a pain to debug.

Just use a basic for-loop until they bring closures into the language

Answer 2

There is JXPath.

Answer 3

You can try Quaere. I didn't use it but it looks interesting.

Answer 4

The Google Collection Library offers this kind of helper method, a bit more cleanly than commons-collections.

Answer 5

By using the lambdaj library, for example you could find the top reputation users as it follows:

List<User> topUsers = 
    select(users, having(on(User.class).getReputation(), greaterThan(20000)));

It has some advantages respect the Quaere library because it doesn't use any magic string, it is completely type safe and in my opinion it offers a more readable DSL.

Answer 6

Querydsl provides this functionality as well via its Collections module. I am biased since I am the maintainer of the module, but I believe given the constraints of Java 6 this is an option.

With Java 7 there will be closures which enable filtering via closures, which makes usage of external libraries less necessary.