Alternate JVM Languages

Abhijeet Lele
Vladimir Zakharov
Goldman Sachs
21/04/2011

Goals

Our Guarantee:
You won’t become knowledgeable,
but you will become aware

2

Interview With Josh Bloch

Can you give us an example of code that you are most
proud of creating and explain why?

The Collections framework. It's far from perfect, but it's
proven itself maintainable and pleasant over the years.
Doug Lea built many parts of java.util.concurrent atop it.
And I still get letters from programmers telling me how
much more pleasant it makes their jobs. It lets you write
stuff like this little program, which computes all the
anagrams in the file on standard input.

From “2008 JavaOne Conference - Rock Star Joshua Bloch”
http://java.sun.com/javaone/sf/2008/articles/rockstar_joshuabloch.jsp

4

Anagram Algorithm: How It Works

5

Java Example
import java.util.*;
public class Anagram {
public static void main(String[] args)
{
int minGroupSize = Integer.parseInt(args[0]);
// Read words from input and put into simulated multimap
Map<String, List<String>> anagrams = new HashMap<String, List<String>>();
for (Scanner s = new Scanner(System.in); s.hasNext();) {
String word = s.next();
String alphagram = alphagram(word);
List<String> group = anagrams.get(alphagram);
if (group == null)
anagrams.put(alphagram, group = new ArrayList<String>());
group.add(word);
}
// Print all permutation groups above size threshold
for (List<String> group : anagrams.values())
if (group.size() >= minGroupSize)
System.out.println(group.size() + ": " + group);
}
private static String alphagram(String s)
{
char[] chars = s.toCharArray();
Arrays.sort(chars);
return String.valueOf(chars);
}
} From “2008 JavaOne Conference - Rock Star Joshua Bloch”
http://java.sun.com/javaone/sf/2008/articles/rockstar_joshuabloch.jsp 6

Java Example With Deluxe Features
import java.util.*;
public static void main(String[] args) {
List<String> group = anagrams.get(alphagram); Multimap
if (group == null)
group.add(word);
}
List<List<String>> winners = new ArrayList<List<String>>();
if (group.size() >= minGroupSize) Filter
winners.add(group);
Collections.sort(winners, new Comparator<List<String>>() {
public int compare(List<String> o1, List<String> o2) {
return o2.size()-o1.size(); Sort
}
});
for (List<String> winner: winners)
System.out.println(winner.size() + ": " + winner);
}
Print

private static String alphagram(String s) {
Arrays.sort(chars); Alphagram
}
} Additional code from “The Java™ Tutorial > Collections”
http://download.oracle.com/javase/tutorial/collections/algorithms/index.html 7

What is Groovy?
• Definition
– A lightweight, low-ceremony, dynamic, object-oriented language
– Open sourced under Apache License, version 2.0
– “marvelous, wonderful, excellent, hip, trendy.” (Merriam-
Webster)
• Like Java
– Follows Java semantics
– Seamlessly integrates with Java
– Compiles into Java bytecode
– Extends the Java API and libraries
– Groovy scripts can be injected into Java
• Not like Java
– Dynamic Language
– Closures
– Properties
– Native syntax for lists, maps, and regular expressions
9

Groovy: Alphagram
Java
Arrays.sort(chars);
}

Groovy
String.metaClass.alphagram = {
char[] chars = delegate.toCharArray()
Arrays.sort(chars)
return String.valueOf(chars)
}

Groovy - er
return delegate.toList().sort().join()
}
10

Groovy: Building Multimap
Java
if (group == null)
group.add(word);
}

Groovy
anagrams = (new Scanner(System.in)).toList().groupBy {it.alphagram()}

11

Groovy: Filtering, Sorting, Printing
Java
winners.add(group);
return o2.size()-o1.size();
}
});

Groovy
winners = anagrams.values().findAll { it.size > minWordCount }
winners = winners.sort { -it.size }
winners.each { println "${it.size} : $it" }

12

Groovy: Putting It All Together
return delegate.toList().sort().join()
}

minWordCount = args[0].toInteger();

(new Scanner(System.in)).toList()
.groupBy { it.alphagram() }
.values()
.findAll { it.size > minWordCount }
.sort { -it.size }
.each { println "${it.size} : $it" }

13

Java Reminder
import java.util.*;
if (group == null)
group.add(word);
}
winners.add(group);
public int compare(List<String> o1, List<String> o2) { String.metaClass.alphagram = {
return o2.size()-o1.size(); return delegate.toList().sort().join()
} }
});
for (List<String> winner: winners) minWordCount = args[0].toInteger();
} (new Scanner(System.in)).toList()
.groupBy { it.alphagram() }
private static String alphagram(String s) { .values()
char[] chars = s.toCharArray(); .findAll { it.size > minWordCount }
Arrays.sort(chars); .sort { -it.size }
return String.valueOf(chars); .each { println "${it.size} : $it" }
}
}

14

What is Scala?
• Like Java
– Bytecode looks very similar to javac output
– Familiar object-oriented concepts
– Static types, only better (better type inference, better generics,
implicit parameters)
– Performance equivalent to Java
– Java code can depend on Scala code
• Not like Java
– Functional principles
– Closures
– Everything is an object
– No such thing as static
– Greatly improved type inference and generics
– Traits (mixins)
– Pattern Matching

16

Scala: Alphagram
Java
Arrays.sort(chars);
}

Scala

word => word.sorted

Scala With Underbar

_.sorted

17

Scala: Building Multimap
Java
if (group == null)
group.add(word);
}

Scala

val map =
new BufferedReader(new InputStreamReader(System.in))
.readLine().split(" ").groupBy( _.sorted)

18

Scala: Filtering And Sorting
Java
winners.add(group);
}
});

Scala

val winners = map.values.filter(_.size > Integer.parseInt(args(0))).toList
val sorted = winners.sortBy(-_.size)

19

Scala: Printing
Java

Scala

for (winner <- sorted.view)
println(winner.size + ": " + winner)

Scala – Another Way

sorted.view.map(list => list.size + ": " + list).foreach(println)

20

Scala: Putting It Together
new BufferedReader(new InputStreamReader(System.in))
.readLine()
.split(" ")
.groupBy(_.sorted)
.values
.filter(_.length > Integer.parseInt(args(0)))
.toList
.sortBy( - _.size )
.elements
.foreach(winner => println(winner.size + ": " + winner.toList))

21

Java Reminder
import java.util.*;
if (group == null)
group.add(word);
}
winners.add(group);
} new BufferedReader(new InputStreamReader(System.in))
}); .readLine()
for (List<String> winner: winners) .split(" ")
System.out.println(winner.size() + ": " + winner); .groupBy(_.sorted)
} .values
.filter(_.length > Integer.parseInt(args(0)))
private static String alphagram(String s) { .toList
char[] chars = s.toCharArray(); .sortBy( - _.size)
Arrays.sort(chars); .elements
return String.valueOf(chars); .foreach(
} winner => println(winner.size+": "+ winner.toList))
}

22

What is Jython?

• Like Java
– Have access to Java standard libraries and third party libraries
• Not like Java
– Language is Python; latest release conforms to Python 2.5
– Dynamically typed
– Choice of using procedural, object oriented, or functional
programming constructs, or a mixture of the three
– Have access to the Python standard libraries and any pure
Python third party library
• Not like Python
– No access to compiled Python libraries
– Some library features are not available (like fork) due to the
restrictions of the JVM

24

Jython: Alphagram
Java

Arrays.sort(chars);
}

Jython
alpha = lambda l : ''.join(sorted(l))

25

Jython: Building Multimap
Java

if (group == null)
group.add(word);
}

Jython

anagrams = [list(g) for k, g in
itertools.groupby(
sorted(sys.stdin.readline().split(), key =alpha),
alpha)]

26

Jython: Filtering
Java
winners.add(group);

Jython

winners = (f for f in anagrams if len(f) > int(sys.argv[1]))

List comprehension:
<output> for <variables> in <collection> if <filter>
{<output>|<variables> <collection>, <filter>}
э

27

Jython: Sorting
Java
}
});

Jython

winners = sorted(winners, key = lambda t: -len(t))

28

Jython: Printing
Java

Jython

for winner in winners:
print '%i: %s '%(len(winner), winner)

29

Jython: Complete Example
import itertools
alpha = lambda l : ''.join(sorted(l))

winners = [
f for f in
sorted (
[list(g) for k, g in
itertools.groupby(
sorted(sys.stdin.readline().split(), key = alpha),
alpha)],
key = lambda t: -len(t) )
if(len(f) > int(sys.argv[1]))]

print '%i: %s '%(len(winner), winner)

30

Java Reminder
import java.util.*;
if (group == null)
group.add(word);
}
if (group.size() >= minGroupSize) import itertools
winners.add(group); alpha = lambda l : ''.join(sorted(l))
winners = [
return o2.size()-o1.size(); f for f in
} sorted (
}); [list(g) for k, g in
for (List<String> winner: winners) itertools.groupby(
System.out.println(winner.size() + ": " + winner); sorted(
} sys.stdin.readline().split(), key=alpha),
alpha)],
private static String alphagram(String s) { key = lambda t: -len(t) )
char[] chars = s.toCharArray(); if(len(f) > int(sys.argv[1]))]
Arrays.sort(chars);
return String.valueOf(chars); for winner in winners:
} print '%i: %s '%(len(winner), winner)
}

31

Jython: A “Simple” Example
import java.util.*;
def sort_string(buf):
l class Anagram {
public = list(buf)
l.sort()
return ''.join(l)
def get_words():
fp = open('dictionary', 'r')
words = [ l.strip() for l in fp.readlines() ]
words.sort() null)
if (group ==
return words
group.add(word);
def }
get_lists_of_size(list_lists, min_size):
return [ l for l in list_lists if len(l) >= min_size ]
def main():
winners.add(group);
all_anagrams = {}
for word int get_words():
public in compare(List<String> o1, List<String> o2) {
key = sort_string(word)
return o2.size()-o1.size(); a
av
if all_anagrams.has_key(key):
e J ge!
}

rit a
}); all_anagrams[key].append(word)
else:
w u
an lang
all_anagrams[key] = [word]
}
u c ny
Yo alphagram(String s)8){
list_lists = all_anagrams.values()
private static String a
in
winners = get_lists_of_size(anagrams,
winners.sort(cmp=lambda x,y: cmp(-len(x), -len(y)))
Arrays.sort(chars);
} print "%d : %s" % (len(winner), winner)
}

32

What is Clojure?
• Like Java
– Not much, really
– Data structures implement the read-only portion of Collection
– Functions implement Runnable & Callable
• Not like Java
– Dynamic, functional language
– Not object-oriented (!)
– Persistent, immutable data structures
– Lazy sequence abstraction
– Software transactional memory
– Multimethods and ad-hoc hierarchies
– Macros
• Compared to Common Lisp/Scheme
– Persistent, immutable data structures
– First-class Vectors, Sets, and Maps
– Focus on concurrency
– No tail call optimization; explicit calls to recur and trampoline required

34

Clojure: Alphagram
Java

Arrays.sort(chars);
}

Clojure

(defn alphagram [word] (apply str (sort word)))

Clojure anonymous function

(fn [word] (apply str (sort word)))

Clojure with placeholder syntax

#(apply str (sort %))
35

Clojure: Multimap
Java
if (group == null)
group.add(word);
}

Clojure

(group-by alphagram (iterator-seq (java.util.Scanner. System/in)))

Clojure with placeholder syntax

(group-by #(apply str (sort %))
(iterator-seq (java.util.Scanner. System/in)))
36

Clojure: Filtering And Sorting
Java
winners.add(group);
}
});

Clojure
(def words-in (iterator-seq (java.util.Scanner. System/in)))
(defn select-anagrams [words]
(sort-by #(- (count %))
(filter #(> (count %) min-group-size)
(vals
(group-by alphagram words)))))
37

Clojure: Printing
Java

}

Clojure

(doseq [winner (select-anagrams words-in)]
(println (count winner) ": " winner))

38

Clojure: Complete Example
Keeping it functional

(defn alphagram [word] (apply str (sort word)))
(def min-group-size (Integer/valueOf (first *command-line-args*)))
(def words-in (iterator-seq (java.util.Scanner. System/in)))
(defn select-anagrams [words]
(filter #(> (count %) min-group-size)
(vals
(group-by alphagram words)))))

(doseq [winner (select-anagrams words-in)]
(println (count winner) ":" winner))
Let there be bindings!

(let [alphagram #(apply str (sort %))
map (group-by alphagram words-in)
filtered (filter #(> (count %) min-group-size) (vals map))
winners (sort-by #(- (count %)) filtered)]
(doseq [winner winners] (println (count winner) ": " winner)))
39

Java Reminder
import java.util.*;
if (group == null)
group.add(word);
}
winners.add(group);
return o2.size()-o1.size(); (defn alphagram [word] (apply str (sort word)))
} (def min-group-size
}); (Integer/valueOf (first *command-line-args*)))
for (List<String> winner: winners) (def words-in
System.out.println(winner.size() + ": " + winner); (iterator-seq (java.util.Scanner. System/in)))
} (defn select-anagrams [words]
private static String alphagram(String s) { (filter #(> (count %) min-group-size)
char[] chars = s.toCharArray(); (vals
Arrays.sort(chars); (group-by alphagram words)))))
} (doseq [winner (select-anagrams words-in)]
} (println (count winner) ":" winner))

40

What is JRuby?
• Like Java
– Have access to Java standard libraries and third party
libraries
– Runs in a JVM
• Not like Java
– Language is Ruby; latest release conforms to Ruby 1.8.7
– Dynamically typed
– Can compile to class files
– Have access to the Ruby standard libraries and any pure
Ruby third party library
• Not like Ruby
– No access to Ruby native-C API
– No access to Ruby continuations

42

JRuby Example: Alphagram
Java
Arrays.sort(chars);
}

JRuby
word.chars.sort.join

43

JRuby: Multimap
Java
if (group == null)
group.add(word);
}

JRuby
anagrams = words.group_by { |word| word.chars.sort.join }

44

JRuby: Filtering, Sorting, Printing
Java
winners.add(group);
}
});

JRuby

filtered = anagrams.values.select {|array| array.length > 4 } winners =
filtered.sort_by { |array| array.length }
winners.each {|each| puts “#{each.size} : #{each.join(‘, ‘)}"}

45

JRuby: Complete Example

anagrams = words.group_by {|word| word.chars.sort.join}
filtered = anagrams.values.select {|array| array.length > 4}
winners = filtered.sort_by { |array| array.length }
winners.each {|each| puts “#{each.size} : #{each.join(‘, ‘)}"}

46

JRuby: Complete Example – Let’s Make It Better
class String
def collation
self.chars.sort.join
end
end

class Symbol
def to_proc
proc { |*args| args[0].send(self, *args[1...args.size]) }
end
end

module Enumerable

def partitioned_with(&transformer)
group_by(&transformer).values
end

def longer_than(size)
self.select {|e| e.length > size}
end

def sorted_by_size
self.sort_by(&:length)
end

end
47

JRuby: Better Complete Example

groups = words.partitioned_with(&:collation)
winners = groups.longer_than(4).sorted_by_size
winners.each{|each| puts "#{each.size}: #{each.join(', ')}"}

48

Takeaways
• JVM provides a robust, industrial strength, scalable
platform
• You can take advantage of JVM and the rest of the
Java ecosystem without the complexity of Java the
language
• Don’t have to wait for Java to adopt the features
already available in other languages: closures, dynamic
capabilities, rich, humane interfaces
• Not all languages are enterprise ready
– These languages are still worth looking into
• Pragmatic Programmer advice:
Learn a new language every year. When you learn a
new language, you learn a new way to think.

49

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