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Mario Zigliotto
Mario Zigliotto

Reputation: 9015

How do I implement Ruby's ".each" method in Java?

I'm new to Java and wondering how I could go about implementing a method like Ruby's .each to make iterating over classes like Arrays and Lists easier?

Upvotes: 1

Views: 1466

Answers (5)

sheldonh
sheldonh

Reputation: 2724

Consider the command pattern:

http://en.wikipedia.org/wiki/Command_pattern#Java

Upvotes: 0

millhouse
millhouse

Reputation: 10007

While it is true that it's slightly awkward to achieve in standard Java, a couple of the popular libraries (that you may even already be using) offer a Predicate interface that spares you the bulk of writing that much, at least. The great thing is that they also offer thoroughly-tested, proven helper classes that mean you don't have to write the iteration code.

Check out Google Guava's Iterables class - you can do things like filter(), findIf() and removeIf(). If used well, these methods can make for extremely readable results.

Apache's Commons Collections offers something similar in CollectionUtils. Methods like find(), filter() and select() all take a Predicate.

Google Guava also goes further and gives you the Predicates helper which has a whole load of canned Predicate instances - things like isNull, containsPattern and isInstanceOf.

Check them out if you want to avoid reinventing the wheel for this stuff.

Upvotes: 4

Tony BenBrahim
Tony BenBrahim

Reputation: 7290

It gets ugly due to the lack of closures, until Java 8, but here it is:

import java.util.Arrays;
import java.util.Collection;
import java.util.List;


public class EachTest {

    interface ItemProcessor<T>{
        void process(T item);
    }

     static <T> void each(Collection<T> collection, ItemProcessor<T> processor){
        for (T item: collection){
            processor.process(item);
        }
    }

    public static void main(String[] args) {
        List<String> list=Arrays.asList(new String("foo"),"bar");

        EachTest.<String>each(list,new ItemProcessor<String>() {
            @Override
            public void process(String item) {
                System.out.println(item);
            }
        });
    }

}

I think in Java 8, it will be (but don't quote me on that):

public static void main(String[] args) {
    List<String> list=Arrays.asList(new String("foo"),"bar");
    EachTest.<String>each(list,String item=>System.out.println(item));
}

Upvotes: 1

Jon Newmuis
Jon Newmuis

Reputation: 26492

You can't make an each function, like Ruby has, since Java doesn't accept blocks as parameters like Ruby does. You could use an interface and provide an anonymous class definition, but that's way more complicated than just using Java's for each construct. To do for each in Java, you can do something like the following:

String[] myStrings = { "a", "b", "c" };

for (String str : myStrings) {
    // Do something with each String value.
    System.out.println(str);
}

Upvotes: 1

dimme
dimme

Reputation: 4424

You can do it using an Iterator or you can do it with a special version of for:

ArrayList<String> strings = ...;

for (String str : strings) {
    System.out.println(str);
}

Upvotes: 0

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