Open minds leads to freedom

Singleton in Java with Enum types

rnaufal — Tue, 07 Sep 2010 19:31:08 +0000

Java 1.5 introduced the concept of Enum types. They are type-safe constants, which implements equals(), hashCode() and cannot be extended. Each constant can have attributes and override an abstract method created on each Enum class.

Although Singletons are not encouraged, the best way to create it is using Enum types. Here is an example:

public enum Singleton {
    INSTANCE;

    public void sayHello() {
	   System.out.println("Hello World!");
    }
}

And then you call it this way:

Singleton.INSTANCE.sayHello();

Using Enums to create Singletons brings the serialization mechanism already bundled in the Enum type. This technique is described on the Effective Java Second Edition book by Joshua Block.

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Java-Quiz: The Iterator Quiz

rnaufal — Tue, 03 Aug 2010 21:28:26 +0000

Danilo sent us an interesting Java-Quiz from the Java Specialists’ Newsletter created by Olivier Croisier. You have to insert your corrective code in place of the //FIXME comment, following these instructions:

Do not modify his existing code, it’s Perfect (of course).
The FIXME tag shows where you’re allowed to insert your corrective code
He must be able to understand your solution when he comes back (so using Reflection is not an option).

Can you find a solution for it?

final List list = new ArrayList() {{
      add("Hello");
}};
final Iterator iterator = list.iterator();
System.out.println(iterator.next());
list.add("World");
// FIXME : work here while I'm sunbathing
System.out.println(iterator.next());

Later I’ll post my attempt to solve it.

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Eclipse Log4J template

rnaufal — Sun, 09 May 2010 19:56:23 +0000

My friend Bruno sent me an interesting tip on how to create a Log4J template at Eclipse. Just follow these steps:

Go to Window > Preferences > Java > Editor > Templates
Click New
Write the string logger at the field Name (this name will be used to call the template)
At the field Pattern, write the following:

private static final Logger LOGGER = Logger.getLogger(${enclosing_type}.class);
Click OK

The variable ${enclosing_type} refers to the enclosing type name. When you are ready, write down logger on the field class declaration to have a logger added to the class.

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Using Hamcrest and JUnit

rnaufal — Tue, 16 Mar 2010 02:10:52 +0000

Lately I started using the core Hamcrest matchers bundled with the JUnit framework to create more readable unit tests.

Hamcrest matchers were created to improve the readability of unit testing code. It’s a framework which facilitates the creation of matcher objects to match rules specified in unit tests. Some examples will let it to be clearer:

   1 import static org.hamcrest.CoreMatchers.equalTo;
   2 import static org.hamcrest.CoreMatchers.is;
   3 import static org.junit.Assert.assertThat;
   4 
   5 @Test
   6 public void shouldBeTheSamePerson()
   7 {
   8     Person me = new Person( "Rafael" );
   9     Person theOther = new Person( "Rafael" );
  10     assertThat( me, is( theOther ) );
  11 }
  12 
  13 @Test
  14 public void shouldHaveFixedSizeNumbers()
  15 {
  16     List<Integer> numbers = Arrays.asList( 1, 2, 3, 4, 5 );
  17     assertThat( numbers.size(), is( equalTo( 5 ) ) );
  18 }

The first example checks if one Person object is equal to another using the Object equals method, which was overridden in the Person class. The is syntax defines a matcher which is a shorthand to is(equalTo(value)). The second one uses the is(equalTo(value)) matcher to check the size of an integer list of fixed size numbers. The assertThat method is used in conjunction with the is(equalTo(value)) matcher, which makes the test sentence very human readable.

An interesting thing is the possibility to create a custom matcher, like this one which tests if a given list only has even numbers:

   1 public class AreEvenNumbers extends TypeSafeMatcher<Collection<Integer>> {
   2 
   3     @Override
   4     public boolean matchesSafely(Collection<Integer> numbers) {
   5         for (Integer number : numbers) {
   6             if (number % 2 != 0) {
   7                 return false;
   8             }
   9         }
  10         return true;
  11     }
  12 
  13     @Override
  14     public void describeTo(Description description) {
  15         description.appendText("even numbers");
  16     }
  17 
  18     @Factory
  19     public static <T> Matcher<Collection<Integer>> evenNumbers() {
  20         return new AreEvenNumbers();
  21     }
  22 }

And below are two tests which uses the AreEvenNumbers custom matcher:

   1 import static org.hamcrest.CoreMatchers.is;
   2 import static org.junit.Assert.assertThat;
   3 import static br.com.rafael.hamcrest.AreEvenNumbers.evenNumbers;
   4 
   5 @Test
   6 public void shouldHaveOnlyEvenNumbers()
   7 {
   8     List<Integer> numbers = Arrays.asList( 2, 4, 6, 8, 10 );
   9     assertThat( numbers, is( evenNumbers() ) );
  10 }
  11 
  12 @Test
  13 public void shouldNotHaveOddNumbers()
  14 {
  15     List<Integer> numbers = Arrays.asList( 1, 2, 4, 6, 8, 10 );
  16     assertThat( numbers, not( evenNumbers() ) );
  17 }

These two tests use the static factory method evenNumbers to instantiate the matcher on the test code. Not the use of the not matcher on the shouldNotHaveOddNumbers test to assert that no odd numbers are present on the given list. All tests use the static import feature, which turns the test not clean and not cluttered with the class qualification.

I haven’t experienced the other common matchers on unit testing code, like the Beans, Collections and Number ones. I think they turn the tests more readable, clean and easy to change. And you? Have you ever used Hamcrest matcher? If you have other examples of using it, post them here!

Updated: Static imports were added to the testing code.

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The power of pair programming

rnaufal — Fri, 15 Jan 2010 02:08:03 +0000

Some weeks ago I started doing pair programming with some co-workers basically for two things:

code some tasks of an user story

get familiar with a new software code base

I haven’t had an opportunity to put this technique in practice a lot before, but I can say it was extremely important and benefit for the project. Sometimes I was the driver and sometimes I was the observer. The driver is the person who starts coding and the observer is who starts doing the code review. That point is important: code review.

Pair programming encourages the review of the code. Perhaps you won’t have an opportunity to refactor some code as you have when you are pairing with someone. I think code reviews are important because:

Reviews increase code quality, because there are 2 people thinking at the same task at the same time.

Refactoring areas arise in the design where improvements are needed

When you have the strong support of an IDE (as Eclipse), some refactorings (extract method, extract class, introduce parameter) are highly automated

Code is more read than written, two people reading the code can understand a lot more about the code base

New ideas arise because of different point of views

Questions can be solved by the sum of knowledge of the code base

And you? What’s your experience with pair programming?
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My paper MIMECORA-DS added as LNCS at SpringerLink

rnaufal — Thu, 03 Dec 2009 20:59:32 +0000

I’m proud to announce that my paper A Collaborative Support Approach on UML Sequence Diagrams for Aspect-Oriented Software was added as lecture notes in computer science at SpringerLink.

At this paper it is presented an extension based on the default UML meta-model, named MIMECORA-DS, to show object-object, object-aspect and aspect-aspect interactions applying the UML’s sequence diagram.

You can check it out here.
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My first experiences on a Scrum team

rnaufal — Wed, 02 Dec 2009 21:14:36 +0000

I moved to a new job recently, which applies agile methodologies to manage software teams, particularly Scrum, which was adopted to make an effective management of price, estimates, task and resources. It’s my first experience working with an agile process and I’m no doubt it brings a lot of values for a software project.

The Scrum methodology works something like this:

The team works on iterations (called sprints) during from 2 to 4 weeks (it depends on the project, organization..) on features prioritized by the owner(s) and the Scrum master of the project referring to a list of requirements written on a document (called product backlog). The priority is set according to the business value of the feature. The called owner is a representation of the customer. The Scrum master is the person who removes impediments for the team to keep them focused on the tasks and keeps the focus on the sprint goal. More information you can find here.

Every sprint start we estimate some stories and select the work to be done on the current sprint. At the end of the sprint, we have the review and restrospective of was and wasn’t done.

Above are my opinions about this agile methodology working with for a month:

The team is completely committed to the overall goal of the sprint

Members try to help each other as soon as one poses an impediment

Everyone on the team knows which task the others are doing

Every member helps each other to complete their tasks when they finish their ones

The Scrum Master is always there to remove obstacles, clarify the understanding of the stories and help the estimates

The PO acts with the team to give directions and suggestions for the next stepsand how to interact with other areas on the organization

I’m very motivated with Scrum practices and the way we put it in practice, and I know I have to learn a lot more.

Have you ever worked with Scrum? What do you think about this agile methodology?
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Fixing Eclipse buttons for Ubuntu 9.10

rnaufal — Fri, 13 Nov 2009 18:43:17 +0000

I’ve just updated to the new Ubuntu Karmic 9.10 and I’ve found some weird problems running Eclipse. Some buttons didn’t work when they were clicked, but the keyboard shortcuts worked well. It looks like in Eclipse 3.6 the bug will be solved. It looks like it’s a hack between Eclipse SWT and GTK. More information here, here and here.

To fix the problem, just launch Eclipse through this shell script file, assuming Eclipse is installed at /home/rnaufal/eclipse/eclipse:

#!/bin/sh
export GDK_NATIVE_WINDOWS=1
/home/rnaufal/eclipse/eclipse
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Product Owner vs Product Manager

rnaufal — Wed, 11 Nov 2009 11:18:21 +0000

I received from @akitaonrails an interesting article concerning the differences and responsibilities of the product owner and product manager roles.

For the author, the PO must perform:

Articulate the product vision to the team

Define the goals at the beginning of every sprint

Tell the story behind each user story so that the development team understands what is required. So the PO must understand the end user requirements.

Define or help define the user story acceptance criteria so the team knows when they are DONE

Be able to prioritize the stories and be able to negotiate/collaborate on priorities with the team. Negotiate priorities occurs when after taking the top priorities off the backlog; there may be some remaining capacity that the next highest priority story won’t fit in to. So in those cases, a lower priority feature could be picked.

Must be available at all inspect and adapt points to answer questions and help guide the team empirically

On the other side, the PM must perform:

Defining the marketing strategies and outbound marketing communications

Pricing strategies

Understanding the positioning of the product in the market place

Competitive analysis

For me, the PO mainly responsibilities are the ones that highlighted. What do you think about them?
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Effect propagation to code

rnaufal — Wed, 28 Oct 2009 02:20:26 +0000

Reading Michael Feathers’ ‘Working Effectively With LegacyCode’, I found quite interesting his heuristics to trace propagation of effects to code:

Identify a method that will change.

If the method has a return value, look at its callers.

See if the method modifies any values. If it does, look at the method that use those values, and the methods that use those methods.

Make sure you look for superclasses and subclasses that might be users of these instance variables and methods also.

Look at parameters to the methods. See if they or any objects that their methods return are used by the code that you want to change.

Look for global variables and static data that is modified in any of the methods you’ve identified.

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