Yakov Fain's Blog

My notes about everything in IT

ECMAScript 6, block-level functions, and the strict mode

leave a comment »

I was preparing code samples for my ECMAScript 6 (ES6) workshop. ES6 has tons of new language features and programming in the next version of JavaScript is a lot of fun. In particular, ES6 supports block-level functions, so the following code should produce the error “doSomething is not defined”.

    function doSomething(){
      console.log("In doSomething");


And it does if you test it in ES6 Fiddle:


But the best part about ES6 is that you can use it today in your real world projects. Just run it through one of the transpilers, which will convert ES6 to ES5 code ready for deployment in all existing Web browsers. Let’s see how the Babel handles my block-level function:


As you can see, Babel renamed my function to _doSomething, so doSomething is not defined, which is correct.

The Traceur transpiler did pretty much the same trick, and doSomething is not defined:


Now let’s run the same code in the console of the developer’s edition of FireFox, which doesn’t support block-level functions. It behaves differently. Because of the hoisting, the declaration of the function doSomething has been moved to the top of the script and it is defined and works.


Google Chrome (allegedly supports block-level functions) also applies hoisting and invokes doSomething (stable and experimental JavaScript features were enabled). Something is broken here. After quick search I found this ES5 recommendation that in strict mode programmers shouldn’t declare functions in a statement context (ny statement they meant block). Let’s use strict mode and try it again in FireFox:


In strict mode this code gives a syntax error in FireFox. Chrome, Babel, and Traceur still produce “doSomething is undefined” in strict mode. It’s not the end of the world, but get prepared for inconsistent results.

Written by Yakov Fain

May 14, 2015 at 10:22 pm

Posted in ES6, javascript

New Java books and videos

with 6 comments

The second edition of my Java tutorial went on sale.
While this is not my first book, it’s special, because it’s a second edition. When you see a second edition of any book, it means that the first one was successful (i.e. was profitable for the publisher). I don’t remember the exact figures, but I made around $40K in the form of royalties for the first edition.

In the second edition I’ve re-written a half of the book from scratch. The release of Java 8 was THE major release of this 20 year-old super popular programming language, and I had to cover the new syntax and APIs of the language.

I’ve replaced the chapters covering Swing with showing a modern way of developing GUI with JavaFX 8. The chapters about Spring, Hibernate, and JSF are out. The chapters about WebSockets and Logging and Gradle are in.

This book comes with more than 7 hours of professional-grade video screencasts produced by Chad Darby. You can watch several of these videos here.

My special thanks to the technical editors Martijn Verberg and Rajesuwer Singaravelu for providing valuable input about the book content.

Finally, I’d like to thank Wiley editors for their professionalism, and O’Reilly Media that provided a great publishing platform Atlas, which spared me from using MS Word.

In parallel, I was writing a book “Java For Kids”, and the drafts of this book are available at this Web site. At this point I have no official publisher for this book, and the content is available for free (subject to change). I also plan to create a training manual based on this book and start running workshops teaching kids Java programming. These manuals will be available for free for anyone who wants to teach Java.

I hope you’ll enjoy the reading as much as I enjoyed writing these books!

Written by Yakov Fain

April 28, 2015 at 1:11 pm

Posted in java

Partying with IntelliJ IDEA Dart, Java, WebSocket and Glassfish

leave a comment »

Recently I wrote a blog showing how to use the WebSocket protocol to push the data from a Java server to a JavaScript client. This time I’ll keep the same code on the server, but the client will be written in Dart. For this example I was using GlassFish 4.1 server, and IntelliJ IDEA 14.1 with installed Dart plugin. I also have Dart 1.9.1 SDK. My goal was to create one Web application deployable module that would contain both Java and Dart code.

I’ll be brief assuming the the reader has some familiarity with IntelliJ IDEA IDE and the structure of Dart projects. Repeating the same exercise in Eclipse IDE should be a trivial task too.

By the time I was creating this app, I already had an IntelliJ IDEA project with multiple Dart modules. So I wanted to add a new Java module with Dart support to the same project. If you prefer creating a new IDEA project from scratch, instead of creating a new module create a new project. Here’s how I did it:

1. Create a new GlassFish configuration (IDEA menu Run | Edit Configurations) pointing at the existing GlassFish installation.

2. Create a new module of type Java Enterprise selecting GlassFish as an application server Web Application and WebSocket as additional libraries. IDEA will create a project with directories src and web (the latter will contain the WEB-INF dir). I called my module GlassfishWebsocketDart. IDEA will also generate index.jsp, which you can delete.


3. Go to the Project Structure (Cmd ; ) and add GlassFish, GlassFIsh WebSocket, and Dart SDK as dependencies to the module GlassfishWebsocketDart.

4. Create (or copy from an existing Dart module) the files pubspec.yaml and pubspeck.lock into the root dir of your module.

5. Create index.html and main.dart in the web dir. The file index.html can look like this:

<!DOCTYPE html>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="scaffolded-by" content="https://github.com/google/stagehand">



  <div id="output">dart uber</div>

  <script type="application/dart" src="main.dart"></script>
  <script data-pub-inline src="packages/browser/dart.js"></script>

My file main.dart looks as follows:

import 'dart:html';

main() {

  var output = querySelector('#output');

  WebSocket ws = new WebSocket('ws://localhost:8080/GlassfishWebsocketDart_war_exploded/clock');

    output.text = &amp;amp;quot;Connected&amp;amp;quot;;

    output.text = event.data;

6. Open main.dart in the editor and IDEA will show the option Enable Dart support – click on it.

7. Right-click on the pubspec.yaml and run pub build (select the debug mode). It’ll create the folder build with files and dart packages required for deployment.


8. Copy all the files from the build/web dir into the web dir located in the root of your module.

9. In the src directory create the following file WebSocketClock.java

import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.util.Set;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class WebSocketClock {

    static ScheduledExecutorService timer =

    private static Set<Session> allSessions;

    DateTimeFormatter timeFormatter =
    public void showTime(Session session){
        allSessions = session.getOpenSessions();

        // start the scheduler on the very first connection
        // to call sendTimeToAll every second
        if (allSessions.size()==1){
                    () -> sendTimeToAll(session),0,1,TimeUnit.SECONDS);

    private void sendTimeToAll(Session session){
        allSessions = session.getOpenSessions();
        for (Session sess: allSessions){
                sess.getBasicRemote().sendText("Local time: " +
            } catch (IOException ioe) {

10. IDEA can deploy Java web apps in the exploded mode (default) or as an WAR archive. Open the GlassFish configuration (menu Run | Edit), and it should look like this:


11. Run your GlassFish and you should see the server pushing the local time every second. The Chromium browser runs the client’s code in its Dart VM, which properly runs WebSocket client communicating with the Java server.


You may ask, “Will this app work in other browsers that don’t have (and will never have) Dart VM?”. Good question. Theoretically the last two lines in our index.html file should check the presence of Dart VM and replace the references to main.dart with a reference to the JavaScript main.dart.js that was generated by the pub build process.

  <script type="application/dart" src="main.dart"></script>
  <script data-pub-inline src="packages/browser/dart.js"></script>

In practice this may not happen, and you’d get a 404 on “missing” dart.js. Now you have two choices:

a) Manually replace the above two lines with this one:

 <script src="main.dart.js"></script>

b) Add a dependency to your project to use the transformer dart_to_js_script_rewriter to do this replacement automatically. Your modified pubspec.yaml should look like this:

name: 'glassfish_websocket_dart'
version: 0.0.1
description: >
  A web app that illustrates dart, websocket, and glassfish.
  sdk: '>=1.0.0 <2.0.0'
  browser: any
  dart_to_js_script_rewriter: any
  - dart_to_js_script_rewriter

Now run the pub get and pub build and only the JavaScript version will be used. This should be done only if you decide to deploy my useful application in production.

The other improvement that can be done are to create a deployment artifact that builds a WAR file that will include the content from the Dart build folder as well as compiled Java classes. And those who already cut the IDE umbilical cord should automate build and deployment with gradle and gulp.

In April, I’ll be making the presentation “Dart for Java developers” twice. On April 14 I’ll do it online at the New York Dart Users Group, and on April 23 I’ll do a live presentation for the New York Java SIG.

Update for MAC OS users: After upgrading to 10.10.3 GlassFish doesn’t start unless you change the startup line to
/Users/yfain11/glassfish4/glassfish/bin/asadmin start-domain –verbose

Written by Yakov Fain

April 6, 2015 at 5:05 pm

Posted in dart, IDEA, java, Web, WebSocket

How to create a signup screen to minimize the number of users who will sign up

with one comment

I’m wondering if these developers do this on purpose or they are just random people in our profession? I was trying to sign up at this Web site. Had to enter my email and pick a password, which I did. Nobody warned me that the password had to be 8 characters until I pressed the submit button. Then the new window popped up:


Just take a look and try to recreate the line of thinking of the developer of this piece of art:

“I need to let the user enter the password that’s at least 8 characters long. So I’ll hide in the bushes and will quietly wait till the user will make a mistake and enter a shorter password. Then I’ll chuckle: one more fell into my trap. Then I’ll add a cool Whoops message. The instructor in our vocational evening classes told us that the error messages should be shown in red. Makes sense. Let me google how to display the text in red. Got it. There is a Font tag with an attribute color. It was easy. Done.  It would be nice to add a counter to know how many people will enter a short password.  I hope it’ll be covered in the Advanced Programming class that I’m planning to take next year”.

Why some developers hate users so much? The prompt in the password field reads “Enter a password”. Why not add the helpful text prompting to enter at least 8 characters?

Maybe this developer was a rookie? And the QA engineer didn’t notice? And the manager never tried to sign up? And the site owner didn’t care?

It’s all about caring. If you care about your users, you’ll find a way to do it right.

And the biggest irony is that the name of this Web site is Skills Matter. Indeed. That’s why I’m not going to sign up for their services.

Update. Two days after writing this blog I decided to registered at the Vimeo video site. They were also hiding in the bushes with the same password length error. Is is something wrong with me? Am I being too picky?


Written by Yakov Fain

March 16, 2015 at 1:56 am

Posted in java

Tagged with ,

Am I still a Java Developer?

with 12 comments

This morning I got the following email from a Java developer: “It seems you are doing less Java and more web development every year.” This got me thinking, and I decided to write this blog.

Am I still a Java developer after 17 years of using this language? I certainly am. But in today’s world using just one programming language is almost impossible unless you’re willing to limit yourself to the server-side development. I’m not saying this is bad – it’s a huge field for never ending self-education and research. Even from the career perspective becoming an expert in a specific Java field can put bread and butter on your table for years to come. For example, Java experts specializing in performance tuning can charge several times more than a typical Java developer. Some people become experts in security or concurrent programming, which allows them to eat an omelet with truffles for breakfast daily.

But 95% of Java developers are doing more or less routine work, and learning other languages and tools can bring some excitement in their lives and make them more competitive in the job market.

While Java is the server-side king, HTML/JavaScript/CSS (a.k.a. HTML5) rule on the client. You can use HTML5 for creating a cross-platform UI for desktop and mobile applications. People use a variety of languages and frameworks to develop Web applications that we use daily. If you already know Java, why not come out of the closet and explore the huge and ever growing HTML5 world?

Traditionally many Java developers look down on JavaScript developers with a false assumption that real development is happening only in Java. I can reveal a secret: this is wrong. JavaScript is as close to the Web what as C language is to the hardware. Just look at this long list of compilers from different languages that generate JavaScript. In our company we use Google Dart as a way to produce JavaScript. Next year we’re planning to switch to programming in the new version of JavaScript (EcmaScript 6 spec will be finalized this summer).

Lots of popular IDEs offer great support for developing and debugging JavaScript. Every Web browser comes with a developer tool allows you to debug JavaScript and monitor everything that goes over the wire during the runtime. The tooling of a modern JavaScript developer has everything that Java developers are accustomed too:

node.js – JS framework plus a runtime for all development tools listed below
npm – node package manager used for installing and managing development tools
bower – package manager for the application dependencies
grunt – a build automation tool
yeoman – a scaffolding tool for generating the initial structure of an application for various frameworks

I teach JavaScript classes for Java developers several times a year. A typical feedback is “I thought JavaScript is a toy, but it’s a serious programming ecosystem worth learning and mastering”. And this is what I do while remaining a Java developer.

Written by Yakov Fain

March 6, 2015 at 1:46 pm

Posted in java, javascript

Why I Rejected a LinkedIn-Originated Offer of 10 Million Euros

with 10 comments

LinkedIn is a popular social network for connecting professionals, and I have an account there. Every day I get an invite to connect with someone. Typically I ignore these invites unless I know the person. But I’ve never received invites to connect from a chair of board of directors of a bank. Till yesterday.  So I’ve accepted the invite.

Then I’ve received an LinkedIn email from this woman stating that she had a business proposition for me, and if I was interested, she was ready to explain. She also provided her email that ended in outlook.com. I checked her LinkedIn profile again. Looked legit. She even had a Twitter account with recent tweets in two languages.

I responded that I was ready to hear about this business proposition. Next day I’ve received a long email from her explaining how she had a private client named Lewis Fain who initially deposited €19M  in their bank and she helped him to grow the wealth to €22M, but unfortunately he died in a car crash. She’s ready to wire transfer me the money, in one condition: we’d split the amount in half so she could improve the wellbeing  of her family. She also asked me not to ruin her career in the bank if I was not interested.

At this point it was clear that it was a new type of a scam that involved creating  fake LinkedIn accounts and impersonating themselves as someone else. Still I decided to continue my treasure hunt and responded to my fake banker asking her to send me any email from her bank email account. She responded again, stating that she understood my concern, but couldn’t use her bank email for such a delicate matter. But to establish trust, she attached a photo of her bank ID.

At this time I had enough of materials for this blog and responded wishing her good luck in finding another heir of poor Lewis Fain. Then I decided to report this scam to LinkedIn. To my surprise this banker was not in my connections list any longer. I searched by her name in LinkedIn, and found the account of that banker, the profile looked different and she didn’t have any connections.So either someone else reported this as a stolen account, or the con artists have removed it programmatically. I’ve reported this account to LinedIn anyway.So beware of LinkedIn initiated scams.

One more warning. Even if this banker would have sent me an email from the account that ended with the bank name, this would not be enough. Being a programmer, I can easily write a program that would send an email with any address in the “Reply To” field. Here’s how a fragment of the Java code to wannabe con artists:

Message emailMessage = new MimeMessage(session);

emailMessage.setFrom(new InternetAddress("MaryLou@thefakebank.com")); 
                                 InternetAddress.parse(emailRecipient, false));
emailMessage.setSentDate(new Date()); 

So if you want to confirm someone’s identity, you need to send an email to the provided email address and receive a response back. Hope this helps.

Written by Yakov Fain

February 27, 2015 at 2:43 pm

Posted in java

Tagged with

JavaFX 8: The keyboard events are not being processed if a scene has only shapes

with one comment

I ran into an interesting problems with JavaFX. When the GUI is done in FXML it seems that if a scene has only shapes (e.g. Rectangle, Circle, etc.) the handler method doesn’t receive keyboard events. And the problem seems to be that there is no way (at least I don’t see it) to give a focus to such a scene. I found a workaround, but I’d appreciate if someone could offer a cleaner solution or confirm that this is a JavaFX bug.

Here’s a code sample that illustrates the problem and the solution:

1. Here is the main application:

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Main extends Application {

  public void start(Stage primaryStage) throws Exception{
   Parent root = FXMLLoader.load(getClass().getResource(&quot;sample.fxml&quot;));

   primaryStage.setScene(new Scene(root, 300, 300));

  public static void main(String[] args) {

2. Here’s the sample.fxml that works, except I don’t need a Button there:

&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;

&lt;?import javafx.scene.control.*?&gt;
&lt;?import java.lang.*?&gt;
&lt;?import javafx.scene.*?&gt;
&lt;?import javafx.scene.shape.*?&gt;
&lt;?import javafx.scene.control.Button?&gt;
&lt;?import javafx.scene.Group?&gt;

&lt;Group fx:id=&quot;theGroup&quot; onKeyPressed=&quot;#keyHandler&quot; focusTraversable=&quot;true&quot;
       xmlns=&quot;http://javafx.com/javafx/8&quot; xmlns:fx=&quot;http://javafx.com/fxml/1&quot;
       &lt;Button /&gt;
       &lt;Rectangle fill=&quot;BLUE&quot; height=&quot;300.0&quot;  stroke=&quot;BLACK&quot;
                              strokeType=&quot;INSIDE&quot; width=&quot;300.0&quot; /&gt;


3. Here’s the Controller.java:

package sample;

import javafx.fxml.FXML;
import javafx.scene.Group;
import javafx.scene.input.KeyEvent;

public class Controller {

  @FXML Group theGroup;

  public void initialize(){
     theGroup.setFocusTraversable(true); // doesn't have any effect
     theGroup.requestFocus(); // doesn't have any effect

  public void keyHandler(KeyEvent event){
    System.out.println(&quot;A Key was pressed&quot;);

This application works and prints the message “A Key was pressed” as long as I keep the <Button> tag in FXML (it’s not visible on GUI because the Rectangle covers it). This is my workaround to make sure that event handler works and prints the message.  Remove the <Button> tag from FXML, and the application won’t process the keyboard events. The problem seems to be that if the FXML has only shapes, it can’t get the focus. The code in the initialize() method doesn’t help to set the focus on a Group container.If anyone could find an explanation of why this code  doesn’t work without a <Button>, please let me know.

Update: The user jewelsea on Stack Overflow suggested to set the focus after  calling  primaryStage.show(); http://stackoverflow.com/questions/28506855/javafx-8-the-keyboard-events-are-not-being-processed-if-a-scene-has-only-shapes.

This gave me an idea how to do it. I’ve added one line root.requestFocus(); at the end of the start() method. No <Button> is needed in FXML and no initialize() method is needed in the Controller.




Written by Yakov Fain

February 13, 2015 at 6:50 pm

Posted in java

Tagged with


Get every new post delivered to your Inbox.

Join 165 other followers