Java 8 it's easy : Higher-order Function

higher-order what?

Higher-order means that it is possible to pass to a method both values and functions and in the same way the method itself can return either a value or a function.

Example:

   •    public void doSomething(String name, Function someFunction){...}

   •    public Function createAnAction(Integer someInteger)

EASY!!!!

Use case 1:

Print a message with weight information in kilos. 

This is easy : 

package com.marco.higherOrder;

public class Printer {

        public void print(int weight) {

                System.out.println("Printing : your weight is " + weight + " kilos");

        }

        public static void main(String[] args) {

                Printer printer = new Printer();

                printer.print(65);

        }

}

Use case 2:

I need to be able to print different weight unit like stone and pounds.

Ok, just put an if and shut up!!

Putting an if it means to add and pass a boolean and then check that boolean and put a boring if/else.

Also what about open close principle? what if we need to add yet another weight unit?

Higher-order Function to the rescue:

I want a class in charge of handling different weight units :

package com.marco.higherOrder; public class Scale {         public String toStones(int weight) {                 return "your weight is " + weight + " stones";         }         public String toKilos(int weight) {                 return "the weight is " + weight + " kilos";         }         public String toPounds(int weight) {                 return "the weight is " + weight + " pounds";         } }

Then I can add a Function in my Printer.print method and pass functions:

package com.marco.higherOrder; import java.util.function.Function; public class Printer {         public void print(int weight, Function<Integer, String> scale) {                 System.out.println("Printing : " + scale.apply(weight));         }         public static void main(String[] args) {                 Printer sender = new Printer();                 Scale scale = new Scale();                 sender.print(65, scale::toKilos);                 sender.print(65, scale::toStones);                 sender.print(65, scale::toPounds);         } }

Function<Integer, String> means that this function will accept an Integer and will return a String.

 scale::toKilos means that the method toKilos of the scale instance will be called.

EASY!!!!

What if I don't need the Scale class?

Then don't don't it :)!!!

package com.marco.higherOrder; import java.util.function.Function; public class Printer {         public void print(int weight, Function<Integer, String> scale) {                 System.out.println("Printing : " + scale.apply(weight));         }         public static void main(String[] args) {                 Printer sender = new Printer();                 sender.print(65, p -> "your weight is " + p + " kilos");                 sender.print(65, p -> "your weight is " + p + " stones");                 sender.print(65, p -> "your weight is " + p + " pounds");         } }

p -> "your weight is " + p + " kilos" the p is simply the int that will be passed to the method.

Functional it’s easy , don’t trust who says it’s hard!

Have a great weekend

Ciao.

Java 8 : Null? no thanks!

You know, I know, they know, everybody knows, returning null from a public method is often a bad practice.
Reasons are multiple, from the risk of raising NullPointerException in runtime to the horrible == null check in your code.

To avoid returning nulls in Java 8 you can use java.util.Optional (if you are on previous version of Java, Guava has similar functionality).

package com.marco;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
public class NoNullsThanks {

        private final Map<String, Integer> nameAge = new HashMap<String, Integer>();

        public Integer getAge(String name) {
                return Optional.ofNullable(nameAge.get(name)).orElse(-1);
        }

        private final Map<String, List<String>> nameEmails = new HashMap<String, List<String>>();

        public List<String> getEmails(String name) {
                return Optional.ofNullable(nameEmails.get(name)).orElse(new ArrayList<String>());
        }
}

Nice & Clean :)

Tridimensional developers

Working in the industry for a while, I noticed different behaviors between developers.

These differences are mostly related to their personalities, their team spirit and finally their entrepreneurship skills.

I identified 3 types or better 3 dimensions in which I can fit all the people I work and worked with.
Before starting and describing these dimensions, I just want to point out couple of important things.

1. This has nothing to do with how good you are with the code or design or testing. You can be the best kickass-bruce-lee-coder, but still entering in the mono-dimensional category.
2. This has also nothing to do with your level of seniority, I saw Juniors that can perfectly fit in the tridimensional category and team leaders falling in the mono-dimensional one. 
3. This is perfectly applicable to ANY workplace and ANY type of job and ANY industry.
4. It is just my point of view in a boring Friday afternoon.

So lets start :)

Mono-Dimensional Developer

You work daily at your stories/tasks

You participate to meetings about process and technologies

You communicate with other team members about status
updates, risks and issues encountered

You create and/or maintain software applications 

You keep updated yourself about emerging technologies and trends

Bidimensional Developer 

You cover the Mono-dimensional points

You help team members without being asked directly

You share with your team what you learned using slides/blogs/etc.

You actively participate to process and technology meetings, asking questions and/or proposing solutions.

Tridimensional Developer

You cover the Bidimensional points

You create, propose and promote new processes and technologies

You take team building actions when needed without being asked directly

You actively participate to meetings other than process and technology

You create blogs/wikis/etc in order to facilitate communication without being asked directly

You see opportunities everywhere and you act on them.

So which developer are you?

Friday-Benchmarking Functional Java

Lets image your product owner goes crazy one day and he asks you to do the following :

From a set of Strings as follows :

"marco_8", "john_33", "marco_1", "john_33", "thomas_5", "john_33", "marco_4", ....

give me back a comma separated String with only the marco's numbers and numbers need to be in order. 

 Example of expected result :

"1,4,8"


I will implement this logic in 4 distinct ways and I will micro benchmark each one of them. The ways I'm going to implement the logic are :

• Traditional java with loops and all.
• Functional with Guava 
• Functional with java 8 stream
• Functional with java 8 parallelStream

Code is below or in gist

package com.marco.brownbag.functional;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
import com.google.common.base.Function;
import com.google.common.base.Joiner;
import com.google.common.base.Predicates;
import com.google.common.collect.Collections2;
import com.google.common.collect.Ordering;
public class MicroBenchMarkFunctional {

        private static final int totStrings = 200000;

        public static void main(String[] args) {

                Set<String> someNames = new HashSet<String>();

                init(someNames);

                for (int i = 1; i < totStrings; i++) {
                        someNames.add("marco_" + i);
                        someNames.add("someone_else_" + i);
                }

                System.out.println("start");

                run(someNames);

        }

        private static void run(Set<String> someNames) {
                System.out.println("========================");
                long start = System.nanoTime();
                int totalLoops = 20;
                for (int i = 1; i < totalLoops; i++) {
                        classic(someNames);
                }
                System.out.println("Classic         : " + ((System.nanoTime() - start)) / totalLoops);

                start = System.nanoTime();
                for (int i = 1; i < totalLoops; i++) {
                        guava(someNames);
                }
                System.out.println("Guava           : " + ((System.nanoTime() - start)) / totalLoops);

                start = System.nanoTime();
                for (int i = 1; i < totalLoops; i++) {
                        stream(someNames);
                }
                System.out.println("Stream          : " + ((System.nanoTime() - start)) / totalLoops);

                start = System.nanoTime();
                for (int i = 1; i < totalLoops; i++) {
                        parallelStream(someNames);
                }
                System.out.println("Parallel Stream : " + ((System.nanoTime() - start)) / totalLoops);

                System.out.println("========================");
        }

        private static void init(Set<String> someNames) {
                someNames.add("marco_1");
                classic(someNames);
                guava(someNames);
                stream(someNames);
                parallelStream(someNames);
                someNames.clear();
        }

        private static String stream(Set<String> someNames) {
                return someNames.stream().filter(element -> element.startsWith("m")).map(element -> element.replaceAll("marco_", "")).sorted()
                                .collect(Collectors.joining(","));
        }

        private static String parallelStream(Set<String> someNames) {
                return someNames.parallelStream().filter(element -> element.startsWith("m")).map(element -> element.replaceAll("marco_", "")).sorted()
                                .collect(Collectors.joining(","));
        }

        private static String guava(Set<String> someNames) {
                return Joiner.on(',').join(
                                Ordering.from(String.CASE_INSENSITIVE_ORDER).immutableSortedCopy(
                                                Collections2.transform(Collections2.filter(someNames, Predicates.containsPattern("marco")), REPLACE_MARCO)));

        }

        private static Function<String, String> REPLACE_MARCO = new Function<String, String>() {
                @Override
                public String apply(final String element) {
                        return element.replaceAll("marco_", "");
                }
        };

        private static String classic(Set<String> someNames) {

                List<String> namesWithM = new ArrayList<String>();

                for (String element : someNames) {
                        if (element.startsWith("m")) {
                                namesWithM.add(element.replaceAll("marco_", ""));
                        }
                }

                Collections.sort(namesWithM);

                StringBuilder commaSeparetedString = new StringBuilder();

                Iterator<String> namesWithMIterator = namesWithM.iterator();
                while (namesWithMIterator.hasNext()) {
                        commaSeparetedString.append(namesWithMIterator.next());
                        if (namesWithMIterator.hasNext()) {
                                commaSeparetedString.append(",");
                        }

                }

                return commaSeparetedString.toString();

        }
}

Two points before we dig into performance :

1. Forget about the init() method, that one is just to initialize objects in the jvm otherwise numbers are just crazy.
2. The java 8 functional style looks nicer and cleaner than guava and than developing in a traditional way :).

Performance:

Running that program on my mac with 4 cores, the result is the following :


========================
Classic              : 151941400
Guava               : 238798150
Stream              : 151853850
Parallel Stream : 55724700
========================

Parallel Stream is 3 times faster. This is because java will split the job in multiple tasks (total of tasks depends on your machine, cores, etc) and will run them in parallel, aggregating the result at the end.
Classic Java and java 8 stream have more or less the same performance.
Guava is the looser.


That is amazing, so someone could think:
"cool, I can just always use parallelStream and I will have big bonus at the end of the year". 
But life is never easy. Here is what happens when you reduce that Set of strings from 200.000 to 20

========================
Classic              : 36950
Guava               : 69650
Stream              : 29850
Parallel Stream : 143350
========================

Parallel Stream became damn slow. This because parallelStream has a big overhead in terms of initializing and managing multitasking and assembling back the results.
Java 8 stream looks now the winner compare to the other 2.

Ok, at this point, someone could say something like :
"for collections with lots of elements I use parallelStream, otherwise I use stream"
That would be nice and simple to get, but what happens when I reduce that Set again from 20 to 2?
This :

========================
Classic              : 8500
Guava               : 20050
Stream              : 24700
Parallel Stream : 67850
========================

Classic java loops are faster with very few elements.

So at this point I can go back to my crazy product owner and ask how many Strings he thinks to have in that input collection. 20? less? more? much more?


Like the Carpenter says :

Measure Twice, Cut Once!!

 

 

Migrate your project from SVN to Git Stash in few steps

Step by step guide on how to migrate your SVN repository with all its history to the Stash, the Atlassian git manager.

Only once :

1. add the ssh key
2. open a terminal 
3. create the authors.txt file in ~/Documents/ 
4. git config svn.authorsfile ~/Documents/authors.txt 

authors.txt format :

username = Name LastName <email>

example :

gordof = Gordon Flash <gordon.flash@superhero.com>
marcoc = Marco Castigliego <marco.castigliego@superhero.com>

For each project :

For this example I will migrate a project called super-hero-service.

1. Tell your team members to not commit on the project during the process.
2. Open a terminal
3. cd ~
4. mkdir migration
5. cd migration
6. git svn clone svn+ssh://marcoc@svn.superhero.com/com/super/hero/Services/ --trunk=super-hero-service super-hero-service
7. go to take a coffee
8. cd super-hero-service
9. git svn show-ignore (Which outputs everything in the SVN ignore property to the console. Then you can copy this to a new file called .gitignore at the root of your repository.Add and commit the file.)
10. go to https://stash.superhero.com/projectsServices and create a repository called super-hero-service
11. git remote add origin ssh://git@stash.suoperhero.com:2022/services/super-hero-service.git
12. git push -u origin master

Java 8 : Functional VS Traditional

The business logic is the same :

Given a String expression composed of visits / time like : "1/24h,1..3/3h,5/*"
Then the result should be the following list of Strings 
"1/24h",
"1/3h","2/3h","3/3h",
"5/1h","5/2h","5/3h","5/4h","5/5h",until ,"24/1h"


So, 2 things need to be solved, the dots and the stars for the visits and for the time.

I will use Java 8 , but  I'll show you the difference between implementing this logic using Functional  and implementing it in a traditional way with loops and ifs.

package com.marco;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
public class ExpressionConverter {
        private static final String COMMA = ",";
        private static final String SEPARATOR = "/";

        private final ImmutableList<Function<String, List<String>>> visitFunctions;
        private final ImmutableList<Function<String, List<String>>> timeFunctions;

        public ExpressionConverter(DotsVisitFunction dotsVisitFunction, StarVisitFunction starVisitFunction, StandardFunction standardFunction,
                        StarTimeFunction starTimeFunction) {
                this.visitFunctions = ImmutableList.of(dotsVisitFunction, starVisitFunction, standardFunction);
                this.timeFunctions = ImmutableList.of(starTimeFunction, standardFunction);
        }

        public List<String> convertVisitTimeExpressionFunctional(String visitTimeExpression) {
                return Lists.newArrayList(visitTimeExpression.split(COMMA)).parallelStream().filter(it -> !it.isEmpty())
                                .map(it -> interpretSingleExpressionFunctional(it)).flatMap(it -> it.parallelStream()).collect(Collectors.toList());
        }

        public List<String> convertVisitTimeExpressionTraditional(String visitTimeExpression) {
                List<String> result = new ArrayList<String>();

                for (String singleVisitTime : visitTimeExpression.split(COMMA)) {
                        if (!singleVisitTime.isEmpty()) {
                                result.addAll(interpretSingleVisitTimeExpressionTraditional(singleVisitTime));
                        }
                }

                return result;

        }

        private List<String> interpretSingleExpressionFunctional(String singleExpression) {
                String visit = singleExpression.split(SEPARATOR)[0];
                String time = singleExpression.split(SEPARATOR)[1];
                List<String> result = Lists.newArrayList();

                visitFunctions.stream().map(it -> it.apply(visit)).flatMap(it -> it.stream()).forEach(visitIt -> {
                        timeFunctions.stream().map(it -> it.apply(time)).flatMap(it -> it.stream()).forEach(timeIt -> {
                                result.add(visitIt + SEPARATOR + timeIt);
                        });
                });
                return result;
        }

        private List<String> interpretSingleVisitTimeExpressionTraditional(String singleExpression) {

                String visit = singleExpression.split(SEPARATOR)[0];
                String time = singleExpression.split(SEPARATOR)[1];

                List<String> result = Lists.newArrayList();
                List<String> visists = Lists.newArrayList();
                List<String> times = Lists.newArrayList();

                for (Function<String, List<String>> visitFunction : visitFunctions) {
                        visists.addAll(visitFunction.apply(visit));
                }
                for (Function<String, List<String>> timeFunction : timeFunctions) {
                        times.addAll(timeFunction.apply(time));
                }
                for (String visitIt : visists) {
                        for (String timeIt : times) {
                                result.add(visitIt + SEPARATOR + timeIt);
                        }
                }
                return result;
        }
}

As you can see we have 2 public and 2 private methods, functional and traditional.

Here is a simple test focusing on the performance of the two styles :

package com.marco;
import static org.mockito.Matchers.any;
import static org.mockito.Matchers.anyInt;
import static org.mockito.Matchers.anyLong;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;
import java.math.BigDecimal;
import java.util.Set;
import org.junit.Before;
import org.junit.Test;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
public class ExpressionConverterTest {

        private static final String EXPRESSIONS = "6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,9/65h,6/7400,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        private Cache cache;

        private ExpressionConverter expressionConverter;

        @Before
        public void init() {
                cache = mock(Cache.class);
                expressionConverter = new ExpressionConverter(new DotsVisitFunction(cache), new StarVisitFunction(cache), new StandardFunction(),
                                new StarTimeFunction(cache));

                Set<Integer> totVisists = Sets.newHashSet();
                for (int i = 1; i <= 100; i++) {
                        totVisists.add(i);
                }

                when(cache.getVisits(anyLong(), (BigDecimal) any(), anyInt())).thenReturn(ImmutableSet.copyOf(totVisists));
        }

        @Test
        public void testPerf() {

                long averageTraditional = 0l;
                long averageFuntional = 0l;

                for (int a = 0; a < 10; a++) {
                        long start = System.currentTimeMillis();

                        for (int i = 0; i < 1000; i++) {
                                expressionConverter.convertVisitTimeExpressionTraditional(EXPRESSIONS);

                        }
                        System.out.println("Traditional java " + (System.currentTimeMillis() - start) + " ms");
                        averageTraditional += (System.currentTimeMillis() - start);

                        long start2 = System.currentTimeMillis();
                        for (int i = 0; i < 1000; i++) {
                                expressionConverter.convertVisitTimeExpressionFunctional(EXPRESSIONS);
                        }
                        System.out.println("Functional java " + (System.currentTimeMillis() - start2) + " ms");
                        averageFuntional += (System.currentTimeMillis() - start2);
                }

                System.out.println("Average Traditional java : " + (averageTraditional / 10) + " ms");
                System.out.println("Average Functional java : " + (averageFuntional / 10) + " ms");

        }
}

And this is the output :
Traditional java 1274 ms
Functional java 773 ms
Traditional java 1054 ms
Functional java 531 ms
Traditional java 961 ms
Functional java 493 ms
Traditional java 948 ms
Functional java 492 ms
Traditional java 949 ms
Functional java 491 ms
Traditional java 958 ms
Functional java 481 ms
Traditional java 1004 ms
Functional java 474 ms
Traditional java 949 ms
Functional java 471 ms
Traditional java 947 ms
Functional java 475 ms
Traditional java 942 ms
Functional java 472 ms
Average Traditional java : 998 ms
Average Functional java : 515 ms


Functional is 2 times faster than Traditional. Why?

Because of this : parallelStream()
Parallel Stream will split the job in several tasks leveraging your multicore system.
So can you put parallelStream() everywhere and replace all the stream() methods with parallelStream() ??

No!
The parallelStream()can in fact cause a big degradation of performance if used in the wrong place.
There are loads of posts out there on this argument that should be read before using this feature, but just remember, if you want to use parallelStream() make sure to measure the performance before and after!!!!!!!!!!