Thursday, 10 October 2013

Ubuntu - restarting your network

Don't forget that when you do this over an ssh/putty session then your connection will be dropped:

sudo ifdown -a
sudo ifup -a
sudo /etc/init.d/networking restart

Monday, 24 June 2013

Wordchain puzzle

Word Chains

Taken from

Write a program that solves word-chain puzzles:

Find a chain of words start starting with one particular word and ending with another. Successive entries in the chain must all be real words, and each can differ from the previous word by just one letter. For example, you can get from "cat" to "dog" using the following chain.
The objective of this kata is to write a program that accepts start and end words and, using words from the dictionary, builds a word chain between them. Find the shortest word chain that solves each puzzle

You can turn lead into gold with the following chain:
Try to capture the developer mindset and record how you to got to you solution.

Development process

How did I get to my solution ?  It's all about covergence.  I start out and see where it goes, see what ideas pop up as I go along, see what sticks etc.  My generate approach is as follows:

1) Write Tests - this gets me thinking about how should I represent the data, and helps drive the interface.
2) Start writing code
3) Get to a working solution (it's not always pretty at this point)
4) Refactor Refactor Refactor until I hit a universal truth ie. the code becomes so simple it must be true!

To solve a problem I generally have a series of insghts - by this I mean ideas which seems obviously the right thing to do and possibly are a deep truth of the solution.


distance - Given a "from" word and a "target" the distance is defined to be the number letters which would need to be changed in the "from" word to mutate it to the "target" word.  ie.  cat -> bot has a distance of 2

Here we go:

Write the unit tests - this brings the first decision - should I use List<String>'s or arrays [] to represent the dictionary? Choose [] as it makes the unit tests slightly more readable.

Thought - its going to be difficult testing with a large dictionary having to search through 1000's of words, multiple roots through the wordchain "space".

  • Insight 1: Allow the tests to define the dictionary.

Idea - find a word in the dictionary which has a distance of 1 from the current word, but also contains at least 1 letter contained in the "to" word.  ie. for the wordchain cat -> dog then cot is 1 from cat and 2 from dog.  The only downside is that this strategy will only work for some word chains...

   "cat", "cot", "cog", "dog"


The code is getting fairly complictated - theres lots of edgecases.
Idea - I'll need to keep track of words I've tried which result in dead ends.  Can I exclude these ?  from future searched or can  I?


What happens if I need to go to a word which has no letters in common with the target word?  This is starting to get too complicated.  What I have learned is that I some how need to keep track of what wordchains I've visited which have resulted in deadends.

Idea - I'm thinking that the most reliable solution would be to brute force this, ie. work out every possible word chain.  This will produce some long chains.  Some of the chains would be dead ends and these can be discounted. Visually a brute force approach would look like a word chain tree with branched coming of branches etc.

  • Insight 2: Think of the word chains as a tree to which we can prune dead branches.
  • Insight 3: Use self recursion
  • Insight 4: Use a stack to represent the branches

I'd need to model this tree as a Map<String, Stack<String>> with the key to the map being the root of the branch.

coding ...

This is looking better.  Can I get rid of the Map ?  I think I'm on the right track as the code is getting simpler.  The self recursion is looking good.

Amazing! - I've got something that works, my unit tests are passing.  The sef recursion involves passing a lot of things around which is not ideal, but this a break through.  I can now run refactor run my tests, refactor, run my tests etc. I can now drive hard at the solution and hopefully glean some more insights.

Time to bring in the full size dictionary.  As expected some very long chains are created 50+.  How can I reduce this ?  What about converging from either direction ?  ie dog -> cat and cat -> dog.  Interestingly coming from a different direction reduces the chain length.  The size seems to be dependent on the ordering of the dictionary.

Idea -> Generate a word chain which may contain 30 words.  Randomly shuffle the words then use this list to form the dictionary for another run and so on.  How many times would I need try.  This would by an interesting experiment - I could converge on a word chain by pure luck :)

  • Insight 5:  Backup the chain when the number of words in the chain exceeds some limit

In this way the algorithm will do the pruning for me.  1 line of code !!!
if ( stack.size() > maxDepth ) return false;  // prune checkout

Refactor refactor refactor...

I'm going to split the code up so that the algorithm is concentrated in once class to demonstrate the simplicity of the solution.  The recursive algorithm itself is defined in 10 lines of code.

enough.... :)

Here's my solution

public class WordchainImpl implements Wordchain {
    private String [] dict;
    private int depth;

    public WordchainImpl(String[] wordList, int depth) {
        this.dict = wordList;
        this.depth = depth;

    public WordchainImpl(String[] wordList) {
        this(wordList, 10);

    public String [] getChain( String from, String to ) {
        // check that from and to exists
        if ( ! ( dictHas(from) && dictHas(to) ) ) return new String[0];

        for ( int i=0; i < depth; i++ ) {
            Stack stack = new Stack<>();
            recurse( from, to, stack, i );
            if ( stack.size() != 1 ) return stack.toArray( new String[stack.size()] );
        return new String[0];

    private boolean recurse( String from, String to, Stack stack, int maxDepth ) {
        stack.push( from );
        if( stack.size() > maxDepth ) return false;  // prune
        if ( from.equals( to) ) return true;

        for ( String w: dict) {
            if ( w.length() == from.length() && dif( from, w ) == 1 && !stack.contains(w) ) {
                if ( recurse( w, to, stack, maxDepth ) ) return true;
        return false;

    private int dif( String a, String b ) {
        int dif = 0;
        for ( int i=0; i< a.length(); i++ ) {
            if ( a.charAt(i) != b.charAt(i) ) dif++;
        return dif;

    private boolean dictHas(String word) {
        for ( String s: dict) {
            if ( s.equals( word ) ) return true;
        return false;

Build Instructions

git checkout
cd wordchains
mvn clean install
java -cp target/wordchain-1.0-SNAPSHOT.jar org.coder36.wordchain.FindMyWordchain


Wednesday, 13 March 2013

BDD with Cucumber


Behavioral Driven Development (BDD) in simple terms, allows business owners, developers and testers to collaboratively work together, bound by a "User Story".  User stories are documented in feature files using the gherkin language, along with "scenarios" which when exercised prove that the feature is ready for production.

This blog entry describes a typical setup which can realise the technical aspect of BDD, user stories and automated testing of "scenarios".  Cucumber was originally written in ruby but has been ported to other languages including java.  Here we will look at the Ruby implementation provided by CucumberCapybara and Rspec.


Assuming your are working on windows, download a ruby installer from here and install.  Run:

gem install cucumber
gem install rspec
gem install capybara

Make sure that you run these commands from the "Command Prompt with Ruby and Rails".

At this point you should have a workable ruby environment.


Install the awesome Sublime Text 2.  This will form your gherkin development environment.  Sublime is an excellent editor, blisteringly fast and beautiful.  Start by installing the package manager:

Using the package manager install:
RubyTest   (

The following package is not available in the package manager, so needs to be installed by hand.  This provides feature file syntax highlighting:

cd c:/users/<user>/appdata/Roaming/Sublime Text 2/Packages
git clone Cucumber

For more packages see

The following steps can all be done via Sublime without going near the command line.


Setup the cucumber directory structure:


 Feature: Search the internet for news
 In order to find news
 As an internet user
 I want to be able to search for news web sites

 Scenario: Search for news providers
 Given I am at
 And I enter bbc into the search bar
 When I hit search
 Then I will be presented with a list of hits including BBC - Homepage
 When I select the BBC - Homepage link
 Then I will be navigated to website with title BBC - Homepage

This feature file is written in the "Gherkin" language.   This serves as documentation, requirements and test acceptance criteria and  can be written by business owners.  See here for a fuller description of Cucumber.   

Next we will write the step definitions mapping on to each of the "Given ...". "When..." and "Then" in the feature file.

 Given "I am at $url" do |url|  
      visit url  
 Given "I enter $text into the search bar" do |text|  
      fill_in 'gbqfq', :with => text   
 When "I hit search" do  
      click_button 'gbqfb'  
 Then "I will be presented with a list of hits including $text" do |text|  
      page.should have_content text   
 When "I select the $text link" do |text|  
      click_link text  
 Then "I will be navigated to website with title $title" do |title|  
      page.should have_xpath("//title", :text => title)  

The visitfill_inclick_button, click_link commands are from the Capybara DSL, and are used to drive a browser, via selenium. page.should  comes from Rspec It's all about driving the web page, then testing for content.  Notice that the step_defs are readable, and very obvious.

 require 'capybara'  
 require 'capybara/cucumber'  
 require 'capybara/rspec'  
 Before do  
      Capybara.register_driver :selenium do |app|, :browser => :chrome)  
      Capybara.current_driver = :selenium  

This is the glue which wires everything together and keeps the step_defs clean of clutter:  "Before" is a cucumber hook which runs immediately before the scenario starts executing.  We're using this to configure selenium to use the chrome driver.

Chromium driver

Download the latest Chromium Driver chromium driver and extract into C:/Windows.  Make sure that your chrome browser is up to date.


Now everything is set up, open a ruby window:
cd demo

You should see the chrome browser open up, navigate to, enter bbc into the search panel, then navigate over to the bbc website. Here is the cucumber output:

You can also run the cucumber tests via Sublime - select Tools->Ruby Test->Run all Tests/Feature


I developed this tutorial on a particularly slow internet connection, and I noticed that occasionally, seleniun complained that the browser window was not available (this normally happened on the "Then I will be navigated to website with title BBC - Homepage"  step definition).  I suspect this was a timeout issue.   

I don't like the way selenium dumps output to the command line, interfering with the nicely formatted cucumber output.  There must be a way to stop this?

Monday, 4 February 2013

JBoss 7 logging tips

To fully embrace jboss 7, use the jboss logging mechanism to specify categories and handlers.  It's not the easiest thing to get working, so I've put together a few hints and tips.

1) Use slf4j-api.jar as the logging facade.  Update the dependencies in the pom.xml to exclude everything else.

Be thorough as the slightest presence of log4j or any other logger, overrides the jboss logging mechanism.  In practice the easiest way is to do this it to use Eclipse to view the pom.xml "Dependency Hierarchy" and exclude any other loggers.   

2) Make sure is not on the classpath of the deployment.  Jboss uses by default - I don't know why!

3) Once and handler has been added, restart the server.

4) If logging is still not working, add the following system property:

Monday, 14 January 2013

Jboss 7, not triggering @PostConstruct

Whilst porting a JSF 2 project over to Jboss 7 I came up against a problem of the @PostConstruct not getting triggered within a @ManagedBean. 

So have:

public class MyController {

  public String inp;

  public void init() {
    // do something

  public void setInp( String inp ) {
    this.inp = inp;

  public String getInp() {
    return inp;

Solution - Add the following to the web.xml:


The Jboss provider also works:

See here for a detailed discussion.