Collect property of objects in collection

In C# I can do this:

IEnumerable<long> ids = things.select(x => x.Id);

In Java I have to do this:

Collection<Long> ids = new ArrayList<Long>(things.size());
for(Thing x : things)
   ids.add(x.getId());

Have to do this sort of thing quite a lot now and wonder if there is a more generic way to do this in Java. Could create a method to do it, but then I would have to add an interface with the getId method or something like that... which I can't...

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using Guava, specifically the function interface :

public class ThingFunction implements Function<Thing, Long> {
    @Override
    public Long apply(Thing thing) {
        return user.getId();
    }
} 

and invoked like this (where transform is a static import from Collections2 of guava:

Collection<Long> ids = transform(things, new ThingFunction());

Guava has quite a few other benefits too.

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使用Apache Commons的BeanUtils和Collections：

Collection<Long> ids = CollectionUtils.collect(things,
        new BeanToPropertyValueTransformer("id"));

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In Groovy you would only have to do this:

Set ids = things.collect{ aThing -> aThing.Id}

That would give you all the Ids from all the things in Things as a list.

Here is some info on Groovy, and some differences compared to Java

链接地址: http://www.djcxy.com/p/10068.html

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