If you understand this line, or better still can write this code you can pretty much say that you have understood the essence of Java 8 Lambdas. Certainly in as much as they can be used with collections.
I found this in a recent presentation by Peter Lawrey. (Definitely worth watching the whole presentation when you have a spare hour.)
Anyway the task was to find the 20 most frequent words in a file:
As you can see, with Java 8 this can actually be done in a single (albeit rather long) line.
If you’re not used to lambdas the code might seem a little scary but actually it’s pretty declarative and when you get past the logic reads fairly easily.
package util;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
/**
* Lambdas in one line
*/
public class LambdaTest {
public static List<String> parse(Path path) throws Exception{
return Files.lines(path)
.parallel()
.flatMap(line -> Arrays.asList(line.split("\\b")).stream())
.collect(Collectors.groupingBy(w -> w, Collectors.counting()))
.entrySet().stream()
.sorted(Comparator.comparing(Map.Entry<String, Long>::getValue).reversed())
.limit(20)
.map(Map.Entry::getKey)
.collect(Collectors.toList());
}
public static void main(String... args) throws Exception{
System.out.println(parse(Paths.get(args[0])));
}
}
| Reference: | Java 8 Lambdas in One Line from our JCG partner Daniel Shaya at the Rational Java blog. |
If this is the future then we are doomed.