Java vs Scala vs Clojure

demo.clj

(ns demo-clj.demo)

(defn -main [] (
    (def years
        ["2009-11", "2009-01",
        "2010-01", "2010-12",
        "2010-01", "2010-04",
        "2010-01", "2010-12",
        "2010-12", "2010-04"])

    (def arr (ref []))
    (doseq [s years]
        (let [i (.indexOf @arr s) v (inc i)]
            (if (== i -1)
                (dosync (alter arr conj s 1))
                (dosync (alter arr assoc v (inc (@arr v)))))))
    (println (apply array-map @arr))))

Demo.java

import java.util.Map;
import java.util.HashMap;

public class Demo {
    public static void main(String[] args) {
        String years[] = {
            "2009-11", "2009-01",
            "2010-01", "2010-12",
            "2010-01", "2010-04",
            "2010-01", "2010-12",
            "2010-12", "2010-04"
        };

        Map<String,Integer> map = new HashMap<String,Integer>();

        for(String s : years){
            int count = map.containsKey(s) ? map.get(s) : 0;
            map.put(s,count+1);
        }

        for (Map.Entry entry : map.entrySet()) {
	    System.out.println(entry.getKey() + ", " + entry.getValue());
	}
    }
}

DemoS.scala

import java.util.Map
import java.util.HashMap
import scala.collection.JavaConversions._

object DemoS {
    def main(arg:Array[String]) = {

        val years = Array(
            "2009-11", "2009-01",
            "2010-01", "2010-12",
            "2010-01", "2010-04",
            "2010-01", "2010-12",
            "2010-12", "2010-04"
        )

        val map = new HashMap[String,Int]()

        years.foreach{(s:String) =>
            val count = if(map.containsKey(s)) map.get(s) else 0
            map.put(s,count+1)
        }

        map.foreach{case(key,value) => println(key + ", " + value)}
    }
}