Keep calm and S.O.L.I.D

Last winter I had the chance to attend a talk by Robert.C.Martin(aka Uncle Bob) in Dublin. I think it was awesome. Uncle Bob is the author of Clean Code(I've got it signed by him in person :p) and also is a very influential person in the software industry.

I've been thinking to write something about some of the contributions he did to the industry and post it here on my blog since that talk.

One of the last things he said to us, was to read as much as we could...
Before starting to write this post I thought about those words for a while...
I think that it was a great advice.
Nobody negates that real experience is probably best, but reading books is also very important.
They carry the experiences of persons who were there before and also the rules and the principles those persons discovered and documented on their way.
Don't get me wrong, following rules and principles strictly does not always guarantee success("the world keeps changing") but understanding them can be of great help when facing great challenges.

So finally I decided to write this post about one of the biggest contributions of Uncle Bob to the world of object oriented programming, and that is the S.O.L.I.D principles.

Principle #1 

Single Responsibility Principle

If we have a class that has multiple responsibilities/features/reasons to change; Modifications done to it carry the risk of affecting other parts of the class(other responsibilities/features/reasons to change). 

In other words: Classes that do more than one thing are difficult to maintain. 

SRP says: "A class should have only one reason to change".

Lets have a look at an example:

 public class BMI {  
     //Stuff...  
      public void calculate(int heightInCm,int weightInGrms) {  
      //Implementation...  
     }  
     public void saveResults() {  
      //Implementation...  
     }   
     public TrainingPlan getTrainingPlan() {  
      //Implementation...  
     }  
 }  

As you can see, it is a clear example of a class with multiple reasons to change:

•  Future business requirements might involve us changing the calculate method(e.g different metrics)
•        Future business requirements might involve us changing the way the results are saved.
•        Future business requirements might involve us changing the way the training plan is created based in the BMI.

We don't want all the above mentioned requirement changes to affect the class. If we don't seek for modularity at an early stage of development, we will very easily end up with difficult to maintain software.

What we need to do is think just on the one unique goal that the class will have.
Also we can think in what the class definitely will not do, so we can distiguish the other reasons to change that should not be there. Follow this way of thinking when fixing a violation of the SRP and it will help you detect the classes that you need to extract:

 public class BMICalculator {  
     //Stuff...  
         public void calculate(int heightInCm,int weightInGrms) {  
      //Implementation...  
     }  
     //Other methods that support the main goal of the class...  
 }  
 public class BMIToStorage {  
     //Stuff...  
         public void save(BMIResults results) {  
      //Implementation...  
     }  
     //Other methods that support the main goal of the class...  
 }  
 public class TrainingPlanCreator {  
     //Stuff...  
         public TrainingPlan getTrainingPlan(BMIResults results) {  
      //Implementation...  
     }  
     //Other methods that support the main goal of the class...  
 }  

Principle #2 
Open Close Principle

The motivation behind the Open Close principle is to extend/change behaviour without modifying the existing code. This principle says:

"modules should be open for extension but close for modification".

You probably think, that this sounds very contradictory, but in many OO programming languages like Java, there are mechanisms that will allow you to do this. 

One of those mechanisms is polymorphism. By defining abstract functions/methods

Let's have a look first at a violation of the open closed principle:

 public class Chef {  
      public void prepareMeal(Meal meal) {  
           if(meal.type.equals("veg")) {  
                prepareVeg();  
           }  
           else if(meal.type.equals("nonVeg")){  
                prepareNonVeg();  
           }  
      }  
      private void prepareVeg() {  
           //Implementation...  
      }  
      private void prepareNonVeg() {  
           //Implementation...  
      }  
 }  
 public class Meal {  
      String type;  
 }  
 public class NonVeg extends Meal {  
      public NonVeg() {  
           type = "nonVeg";  
      }  
 }  
 public class Veg extends Meal {  
      public Veg() {  
           type = "veg";  
      }  
 }  

In the above code, if a new requirement arrives saying to make some other type of meal different than veg and non veg, the class will need to be modified. The given above example is not maintainability friendly.

Let's see how to use polymorphism to remove that conditional logic and improve the solution:

 public class Chef {  
      public void prepareMeal(Meal meal) {  
           meal.cook();  
      }  
 }  
 public abstract class Meal {  
      public abstract void cook();  
 }  
 public class NonVeg extends Meal {  
      public void cook() {  
           //...  
      }  
 }  
 public class Veg extends Meal {  
      public void cook() {  
           //...  
      }  
 }  

As you can see the solution is more flexible, now it is easier to maintain and also we got rid of an evil flag that at long term will cause only problems when manipulating it. The class Meal that contains sensitive methods is open for extension but closed for modification.

The OCP principle is very powerful but we also must have in mind that by adding levels of abstraction(as alternative you can also think about Composition versus inheritance), we also increase the complexity and it is very important to understand that this principle should be applied only in those places where there is more likely to be often requirement changes. 

Principle #3 

Liskov substitution principle

This principle is concern about sub-classes classes replacing the behavior of their base class. 

If this occurs, the new classes can produce undesired effects when they are used/called in other parts of the program.

Liskov's Substitution Principle states that if a client is calling a base class, then the reference to the base class should be able to be replaced with a derived class without affecting the functionality of base class.

Lets have a look at an example of violation of this principle:

 public class Duck {  
      public void quack(){  
           //..            
      };  
      public void swim(){  
           //..  
    };  
 }  

Also a wild duck can quack and swim.
But what about Duck toys?

 public class DuckToy extends Duck {  
     private boolean batteriesIncluded;       
      public DuckToy(boolean batteriesIncluded) {  
           //...  
      }  
      public void swim() {  
           //...(This logic depends on the batteries)  
      }  
      public void playSound() {  
           //...  
      }  
 }  

As you see, some duck toys require batteries and also they don't really quack, they just play a sound. Even if there are no compilation errors and it looks tempting to include duck toy in this inheritance chain, this is clear violation of Liskov's substitution principle.
The reason is that if a client instantiates the base class, the derived class DuckToy, is not capable of replace it because the functionality is being affected.

 public class Pond {  
      public static void main(String[] args) {  
           Duck wildDuck = new WildDuck();  
           Duck duckToy = new DuckToy(true);  
           wildDuck.quack();  
           //This should not quack  
           duckToy.quack();  
           //Compilation error, real ducks don't play sounds or use batteries  
           //duckToy.playSound();  
      }  
 }  

One solution in this case could be to have a separate class by its own, to represent the duck toy.

 public class DuckToy {  
     private boolean batteriesIncluded;       
      public DuckToy(boolean batteriesIncluded) {  
           //...  
      }  
      public void swim() {  
           //...(This logic depends on the batteries)  
      }  
     public void quack() {  
           //Duck Toys don't quack  
      }  
      public void playSound() {  
           //...  
      }  
 }  

Principle #4 
Interface segregation principle

This is a very simple to understand principle, it says that clients should not be forced to implement interfaces they don't use Just that simple. Have a look at a violation of this principle:

 public interface Animal() {  
    public void fly();  
    public void run();  
    public void swim();  
 }  
 public class Dog implements Animal {  
    public void fly() {  
    //This is empty because dogs can't fly  
    }  
    public void run() {  
     //Implementation for running  
    }  
    public void swim() {  
     //Implementation for swimming  
    }  
 }  

That was horrible uh? So there are many ways you can avoid this.
One example could be to combine specific interfaces as per needed:

 public interface Runner() {  
    public void run();  
 }  
 public interface Swimmer() {  
    public void swim();  
 }  
 public interface Flyer() {  
    public void fly();  
 }  
 public class Dog implements Swimmer,Runner{  
    public void swim(){}  
    public void run(){}  
 }  
 public class Seagull implements Swimmer,Flyer{  
     public void swim(){}    
      public void fly(){}  
 }  

Degresion: While writing this example I just remembered a post that I wrote time ago about the use of Marker interfaces, that is also another interesting way of getting flexibility using interfaces. 

Principle #5 
Dependency inversion principle

This principle says "Don't depend on anything concrete, depend only on things that are abstract." So make sure that all of your dependencies point at things that are abstract.
This will bring safety to your code and also make it flexible.
Probably you are thinking that this principle, can be a bit radical; but obiously, in real following it always strictly is just very difficult(maybe even impossible).
A tip that you can use to verify that you are following this principle when you call a function, is to program to the interface and not the realization.

One great example of this principle in practice is the Template design pattern. Lets have a look first at a common violation of the principle:

 public class PizzaMaker {  
   public Pizza makeMeatPizza() {  
      Pizza pizza = new Pizza();  
     pizza.setBase(true);  
     pizza.setCheese(true);  
     pizza.setOregano(true);  
     pizza.setTomato(true);  
     pizza.setMeat(true);  
     cook(pizza);  
   }  
   public Pizza makeVeggiePizza() {  
      Pizza pizza = new Pizza();  
     pizza.setBase(true);  
     pizza.setCheese(true);  
     pizza.setOregano(true);  
     pizza.setTomato(true);  
     pizza.setMeat(false);  
     pizza.setVegetables(true);  
     cook(pizza);  
   }  
   private Pizza cook(Pizza pizza) {  
   //...  
   }  
 }  

The above example is a badly coded class that makes 2 types of pizzas... There are many bad things in this piece of code, but I will just focus on the violation of the principle we are discussing.
Since every call done to the pizza object is to a concrete method, what we get is something very rigid and inflexible.
Every pizza has some ingredients that are mandatory, such as the base, tomato, cheese and oregano,but the rest are optional, so: why do we care about making calls to concrete methods, to set those extra ingredients, if is not even our concern?

In the following snippet of code, a template method is introduced to abstract the optional part and let sub-classes implement them.

 public abstract class PizzaMaker {  
  //A method that has a call to an unimplemented abstract function,   
  //is known as a template method  
   public Pizza make() {  
     Pizza pizza = addBasicIngredients();  
     addSpecificIngredients(pizza);  
     cook(pizza);  
     return pizza;  
   }  
   public abstract void addSpecificIngredients(Pizza pizza);  
   private Pizza addBasicIngredients() {  
     Pizza pizza = new Pizza();  
     pizza.setBase(true);  
     pizza.setCheese(true);  
     pizza.setOregano(true);  
     pizza.setTomato(true);  
     return pizza;  
   }  
   private void cook(Pizza pizza) {  
     //...  
   }  
 }  
 public class MeatPizzaMaker extends PizzaMaker {  
   @Override  
   public void addSpecificIngredients(Pizza pizza) {  
     pizza.setMeat(true);  
     pizza.setVegetables(false);  
   }  
 }    
 public class VegetablesPizzaMaker extends PizzaMaker {  
   @Override  
   public void addSpecificIngredients(Pizza pizza) {  
     pizza.setMeat(false);  
     pizza.setVegetables(true);  
   }  
 }  

The S.O.L.I.D principles, were identified by Robert C.Martin, but the Acronym was created by Michael Feathers in the year 2000, today they are well known in the world of object oriented sofwtare and many there is plenty literature on books and internet about them.

Just for the end of this post I would like to share with you a great podcast interview that I found on the web, were Uncle Bob, explains S.O.L.I.D in detail.

http://www.hanselminutes.com/145/solid-principles-with-uncle-bob-robert-c-martin

In London you will never be hungry.

I recently arrived to London, I have to say that I am very impressed.
Everything is really beatiful and the weather is great. One of the things that kept my attention is the huge amount of places you can pick for eating. I love food, and while eating at an Indian place at whitechappel yesterday, I've got inspired for my next blog post.

Did your programming teacher ever gave you that exercise, where you had to create a program to pick some food from a restaurant menu and try to apply some design pattern to it?
While looking through the menu at that Indian place I was remembering that homework, and I think it was some kind of factory pattern what we were expected to use back then to solve it.

This article is about the "abstract factory" pattern. Because of its purpose, some people may also refer to it as the "Toolkit pattern".
Let's have a look at it...

The "abstract factory" pattern is an enhancement of the "factory method" pattern(maybe better to say-It uses it...). Let's just refresh quickly our minds about the "factory method" pattern.

The "factory method" pattern is a creational pattern that intents to release the client from the task of creating objects.
The main reasons are:
 -objects may have a complex/dependant initialization mechanism which does not interest the client.
 -the client doesn't know which is the object type that he needs until runtime.

To implement a factory method what we need is create a method that will take an argument(passed at runtime) and add to it conditional logic that will create one object type or other based on the passed parameter.

The only way in which abstract factory differs from factory method is that with abstract factory we just create factories and let the client use the factories for create objects.

Both "abstract factory" and "factory method" are widely used in software engineering. Now let's have look a simple example where an "abstract factory".

In this UML diagram, we see how the client interacts only with the abstract factory and even the objects that creates using those factories are abstract(Food). The client does not know or care at all how those objects are created. As a result, the client call is simplier and does not have complex conditional logic to decide the object that is required.

 public class Customer {  
   public void orderFood() {  
     System.out.println("Which type of food would you like?");  
     Scanner scanner = new Scanner(System.in);  
     System.out.println("1- Mexican");  
     System.out.println("2- Chinese");  
     System.out.println("3- Indian");  
     int option = scanner.nextInt();  
     FoodFactory factory = FactoryMaker.getFactory(option);  
     Food food = factory.prepareFood();  
     System.out.print("Here are your " + food.getClass().getName());  
   }  
 }  

In the above code we see what we just mentioned above. The client using the abstract factory only interacts with abstractions, so there is not much client code.

 public interface FoodFactory {  
   public Food prepareFood();  
 }  

If we want to extend our software and have some other types of factories, we need to implement the comon interface that the client uses to access the factories.

 public class MexicanFoodFactory implements FoodFactory {  
   @Override  
   public MexicanFood prepareFood() {  
     Scanner scanner = new Scanner(System.in);  
     System.out.println("Mexican food menu:");  
     System.out.println("1- Fajitas");  
     System.out.println("2- Tacos");  
     return getFood(scanner.nextInt());  
   }  
   private MexicanFood getFood(int choice) {  
     switch (choice) {  
       case 1:  
         return new Fajitas();  
       case 2:  
         return new Tacos();  
     }  
     return null;  
   }  
 }  

This code above is just one sample implementation of one of those factories. As you can see, it has a "factory method" pattern in itself that will help return the appropiate food object(Just notice that the return type is an abstract class)

 public class FactoryMaker {  
   public static FoodFactory getFactory(int choice) {  
     switch (choice) {  
       case 1:  
         return new MexicanFoodFactory();  
       case 2:  
         return new ChineseFoodFactory();  
       case 3:  
         return new IndianFoodFactory();  
     }  
     return null;  
   }  
 }  

But to allow the client create the factories we will need some kind of gadget that will allow the client create one factory or other at runtime. That is why we need this class called FactoryMaker(This is again another sample of "factory method" but it will return an abstract/interface type)

 public abstract class Food {  
 }  
 public abstract class MexicanFood extends Food {  
 }  
 public class Fajitas extends MexicanFood {  
 }  

This 3 classes above are just part of the domain model.If you want you can make abstract those that you don't need to instantiate using the "new" keyword. The factories task is to create each of the concrete objects but use abstract return types so the client does not know about the type of the object being returned.

 Even if this pattern looks really interesting there are 2 important disadvantages of using it:
 - the bigger the model gets(more products), the more difficult is to maintain.
 - it violates the open-closed principle

Bon Appetit!

If you break something you have to pay for it!

Many years ago in Spain(as a kid) I was probably in second or third year of primary school, I had to buy a gift for somebody's birthday.
All I had was 500 pesetas(a bit less than 3 euros) and I wanted to buy something cheap, but at the same time beautiful and also decorative.
I was walking around the neighbourhood and not far away from my house, I found a glass craft shop.
I went into the shop and started walking the corridors, there were all sort of glass crafts: from ashtrays to lamps... and everything was all over the place, not just in selves also there were dozens of crafts on the ground.
Quickly I noticed a little figure with a price tag that said 500, that was the gift I wanted to buy. Unfortunately It was in the ground placed at least 2 meters away from were I was, and there were lots of other glass crafts on the way to it. If I wanted to reach it all I could do was move away each of those other crafts that were on the way. I carefully started doing it until I've got the figure I wanted. When I was ready to go back and turned around the shop attendant was looking at me and said: "If you break something you have to pay for it!", I've got a bit scared and... well... is up to your imagination how this story ended.

This story reminds me a bit to the feeling that we all have sometimes when unit testing some code: "Is this really a unit test?".
Sometimes we think we tested correctly but if we are not extra careful with our unit tests we might unconsciously be creating a poisonous integration test.

Let's have a look at an example:

1:  public class ProductDiscountCalculator {  
2:       public void apply50PercentDiscount(Product product) {  
3:            ProductManager manager = new ProductManager();  
4:            if(product.isExpired()) {  
5:                 product.setPrice(product.getPrice() - product.getPrice() * 0.5);  
6:            }  
7:            manager.updateProduct(product);  
8:       }  
9:  }  

We want to unit test the method in the above class and this is what we do:

1:  public class ProductDiscountCalculatorSpecification {  
2:       private ProductDiscountCalculator calculator;  
3:       private Product sampleProduct;  
4:       @Before  
5:       public void arrange() {  
6:            calculator = new ProductDiscountCalculator();  
7:            sampleProduct = new Product();  
8:            sampleProduct.setPrice(10);  
9:            sampleProduct.setExpired(true);  
10:       }  
11:       @Test  
12:       public void priceDiscounted50Percent() {  
13:            calculator.apply50PercentDiscount(sampleProduct);  
14:            assertThat(sampleProduct.getPrice(), is(5D));  
15:       }  
16:  }  

When we run this test, it will go green, but... Is this really a unit test?
What about this line:

 manager.updateProduct(product);  

That line is very dangerous, maybe it is accessing a database and we are poisoning it every time we run our tests.
That's why we need to have extra careful and make sure that we use techniques to break dependencies, stubs, fakes, spies, mocks... or anything
that takes, to make sure at 100% that we are unit testing.
Lets see how we can break the ProductManager dependency and create a more testable alternative:

1:  public class ProductDiscountCalculator {  
2:       private ProductManager manager;  
3:       public ProductDiscountCalculator(ProductManager manager) {  
4:            this.manager = manager;  
5:       }  
6:       public void apply50PercentDiscount(Product product) {  
7:            if(product.isExpired()) {  
8:                 product.setPrice(product.getPrice() - product.getPrice() * 0.5);  
9:            }  
10:            manager.updateProduct(product);  
11:       }  
12:  }  

In the above example we extract the dependency and make sure that we can set it from outside of the class.  We could do it different ways I just used composition for this example.

1:  public class ProductDiscountCalculatorSpecification {  
2:       class ProductManagerStub extends ProductManager {  
3:            @Override  
4:            public void updateProduct(Product product) {  
5:            }  
6:       }  
7:       private ProductDiscountCalculator calculator;  
8:       private Product sampleProduct;  
9:       @Before  
10:       public void arrange() {  
11:            calculator = new ProductDiscountCalculator(new ProductManagerStub());  
12:            sampleProduct = new Product();  
13:            sampleProduct.setPrice(10);  
14:            sampleProduct.setExpired(true);  
15:       }  
16:       @Test  
17:       public void priceDiscounted50Percent() {  
18:            calculator.apply50PercentDiscount(sampleProduct);  
19:            assertThat(sampleProduct.getPrice(), is(5D));  
20:       }  
21:  }  

In what regards to the test I used the subclass and override technique to make sure that we are not poisoning a the database if the real object was passed. Since the object that we are passing to the constructor of ProductDiscountCalculator is just an stub, we are now 100% sure that this was correctly tested without poisonous integration tests.

Duplication - A bit between your teeth

I presume that pretty much everybody who has been in contact with the java programming language either in studies or professionally even for a little bit, knows that duplication is a code smell.
We all know that some consequences of duplication are: less maintainability, less readability, the code is more likely to contain bugs, performance issues... and many more.

I think there should not be need to explain what duplication is, but just in case let's write only one line to define it and also make sure that we understand it:

"Duplication is the existence of multiple copies of a single concept"

Are there any doubts until this point?...
Please go back and read once more the definition if you still are not sure about it.

So, how do we fix duplication?


But if it is so easy to understand what duplication is and also how simple it is to refactor, why do we find it all over the place, no matter what software we are looking at.

Well... there are many reasons why there is duplication all over the place:

• sometimes we just rush to get things done and we don't care about it. 
• maybe we think that refactoring is boring or is not profitable, so we have no patience to do it.
• other times we think there are always more important things to do and duplication is not really affecting us.
•  also sometimes when we want to do something about it, we just can't see it even if it is in front of us.             

 So, what do you think?... Any of this may be the reason why you are not fixing duplication?

If your reason is any of the first 3, I am sorry, but this blogpost will not be of any use to you and the best you can do is close this browser tab or surf somewhere else.

But if it is the 4th, the reason why you are not fixing the duplication, then you might find the following lines very interesting....

This is the secret why many programmers sometimes find it so difficult to deal with duplication...

There are different kinds of duplication, this are some of the most important:

• Literal
• Structural
• Semantic

Literal duplication

This is a very easy to spot kind of duplication. It is basically literal values that are repeated in our code.

e.g

 public class RepeaterSpecification {  
      @Test  
      public void repeatsInput() {  
               assertThat("value",is(repeat("value")));  
      }  
      @Test  
      public void repeatsEmptyInput() {  
              assertThat("",is(repeat("")));  
      }  
     //...  
 }  

The most common way to fix this type of duplication is to create a local variable. Let's have a look at a possible refactor:

 public class RepeaterSpecification {  
      @Test  
      public void repeatsInput() {  
         String input = "value";  
         assertThat(input,is(repeat(input)));  
      }  
      @Test  
      public void repeatsEmptyInput() {  
         String input = "";  
         assertThat(input,is(repeat(input)));  
      }  
     //...  
 }  

It looks like we no longer have literal duplication. But unfortunately as you probably noticed, sometimes when fixing one type of duplication we generate another type of duplication. Keep reading to find out more...

Structural duplication
We can recognize this situation when the logic is duplicated but it operates on different data.
See this situation in the following example:

e.g

 public class RepeaterSpecification {  
      @Test  
      public void repeatsInput() {  
         String input = "value";  
         assertThat(input,is(repeat(input)));  
      }  
      @Test  
      public void repeatsEmptyInput() {  
         String input = "";  
         assertThat(input,is(repeat(input)));  
      }  
     //...  
 }  

As you can see I toke this code from the previous example. The assertThat() operation is identical, the only difference is the data that it uses. Let's have a little look at a way how to fix structural duplication:

public class RepeaterSpecification {  
      
      @Test  
      public void repeatsInput() {  
         assertThatInputIsRepeated("value");  
      }  

      @Test  
      public void repeatsEmptyInput() {  
         assertThatInputIsRepeated("");  
      }
 
      private void assertThatInputIsRepeated(String input) {  
            assertThat(input,is(repeat(input)));
      }
     //...  
 }

Now that we extracted the method that does the assertion we no longer have duplication.

Semantic duplication

This is  the situation where different code implementations represent the same functionality or concept.
The definition of semantic duplication teaches us that duplication can be invisible from the point of view of the code("The definition from the start of this post makes a way more sense now, uh? :)" ). This kind of duplication is probably one of the most difficult to spot.

e.g

public class TeamValidator {       
  
      public boolean isThereALeader(List<Members> team) {  
           Iterator<Member> iterator = team.getIterator();
           while(iterator.hasNext()) {
              Member member = iterator.next();
              String role = member.getRole();
              if(role.equals("Leader"))
                return true;
           }  
           return false;
      }  

      public boolean areThereAtLeast2NewJoiners(List<Members> team) {  
            for(Member member:team) {
                DateTime aMonthAgo = DateTime.now().minusMonths(1);
                if(member.startingDate().isAfter(aMonthAgo))
                return true; 
            }
            return false;   
      }
     //...  
 }

At first glance, when we look at the two methods in the code above we cannot really see much duplication. No matter how much we look at it, we will not see it. Semantic duplication is invisible from the implementation point of view. To spot it what we need to do is spot the behavioral anti pattern that is hidden in the code. If we think about it, basically the repetition going on is that both methods iterate one list of the same type and then apply certain criteria(Completely different implementations but one same concept).
Semantic duplication is more difficult to fix than other types of duplication and often requires a bigger refactoring effort. Here is one possible solution that helps us get rid of it using Java generics:

 public class TeamValidator {      
    public boolean isThereALeader(List<Member> team) {   
         return new LeaderVerifier<Member>().evaluate(team);  
    }   
    public boolean areThereAtLeast2NewJoiners(List<Member> team) {   
         return new NewJoinersVerifier<Member>().evaluate(team);  
    }  
 }  

 public abstract class LoopEvaluator<T> {

 public boolean evaluate(List<T> list) {
  for (T element : list) {
   if(evaluateElement(element)) {
    return true;
   }
  }
  return false;
 }
 
 public abstract boolean evaluateElement(T element);
 
}

public class LeaderVerifier<T extends Member> extends LoopEvaluator<T> {

 @Override
 public boolean evaluateElement(T element) {
  return element.getRole().equals("leader");
 } 
}

public class NewJoinersVerifier<T extends Member> extends LoopEvaluator<T> {

 private int newJoiners;
 
 @Override
 public boolean evaluate(List<T> list) { 
  this.newJoiners = 0;
  return super.evaluate(list);
 }
 
 @Override
 public boolean evaluateElement(T element) {
  DateTime aMonthAgo = DateTime.now().minusMonths(1);
  if(element.startingDate().isAfter(aMonthAgo)) 
   this.newJoiners++;
  return newJoiners == 2;
 }
}

Duplication is not a little topic at all. The 3 types of duplication I mentioned in this post are from my point of view some of the most common but there are many more. Here a link where I found where at the bottom you can find a mention to other kinds of duplication: http://blogs.agilefaqs.com/tag/code-smells/

                                                                     

 I am the spaghetti monster, You cant get rid of me!!!! Hahahaha......

Just to conclude this post, I want to say that I have the impression that duplication many times is an  underestimated code smell that undetected grows and grows and ends up transforming systems into spaghetti monsters.

Lets get rid of it while it is just a bit between your teeth! ;)

How to verify that void methods were called using Mockito

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Mockito is one of the most popular mocking frameworks for java.
This post Is just little miscellaneous where I will show you how to mock and verify a void method call.

Sometimes when we test a call to a void method all we want to do is just make sure that at some point in its life cycle, another method will be called with certain parameters.
Let's see the following example:

 public class SomeClass {  
      private OtherClass otherClass;  
     
      public SomeClass(OtherClass otherClass) {  
           this.otherClass = otherClass;  
      }  
      protected void firstMethod(int value) {  
           if(value > 0) {  
                secondMethod("Yes!");  
           }  
           else {  
                secondMethod("No!");  
           }  
      }  
      private void secondMethod(String value) {  
           otherClass.someMethod(value);  
      }       
 }  

In the above piece of legacy code the most important part is a method called "someMethod()". We must make sure that it is called in a proper way, but unfortunately it belongs to a dependency to which we have no access and also to make it more complicated it is inside a private method.

Mockito framework could help us mock and verify that method call.
Here is how we can do it:

 package demo;
 import static org.mockito.Mockito.verify;  
 import org.junit.Before;  
 import org.junit.Test;  
 import org.mockito.Mock;  
 import org.mockito.MockitoAnnotations;  
 import code.OtherClass;  
 import code.SomeClass;  
 public class TestClass {  
      @Mock  
      private OtherClass otherClass;  
      //Class under test  
      private SomeClass someClass;  
      @Before  
      public void prepareDependencies() {  
           MockitoAnnotations.initMocks(this);       
           someClass = new SomeClass(otherClass);  
      }  
      @Test  
      public void is_the_value_greater_than_zero() {  
           someClass.firstMethod(8);  
           verify(otherClass).someMethod("Yes!");  
      }  
      @Test  
      public void is_the_value_smaller_than_zero() {  
           someClass.firstMethod(-1);  
           verify(otherClass).someMethod("No!");  
      }  
 }  

The most important things to highlight in this test class are:

• The class under test is never mocked.
• The dependencies of the class under test need to be mocked.
• By calling a method on a mock object we will mock that method call
• By using the verify() method we will test that at some point the method from the mock was called  with the exact same parameters.
• The test class can access the protected method because the package name is the same.(But of course in your project structure test will be under src/test/java and production code under src/main/java)

Using transaction attributes in EJB 3.1 - Container Managed Transactions

When somebody refers to container managed transactions, what we understand is that the EJB container is responsible of managing transactionality for the methods inside EJB's deployed in the EJB container.

The theory behind transaction management in EJB 3.1 is not brief and probably my post would become to long if I tried to explain other important concepts. In this post I want to just focus on an important concept known as the transaction attribute.

To simplify this concept, I will refer to it, as a configuration given to a method/function within an EJB, that will tell the EJB container what to do with the incoming transaction when that method is called.

The thing that will determine what will occur with the transaction when a certain transaction attribute is used will be the transactional context from where the method was called. In other words, if the enterprise method annotated with a certain attribute was called from a non-transactional(e.g a web page) will manage the transaction differently than if it was called from a transactional context(e.g another EJB). And this is the reason why sometimes we have to choose wisely our transaction attributes.

To use transaction attributes in our EJB's its very simple, all you need to do is use an annotation:

 @Stateful  
 public class SomeBean implements SomeInterface {  
   @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)  
   public void someMethod(){  
    //...  
   }  
   //...  
 }  

Now that we know how to annotate the methods, lets see what will occur when each of the transaction attributes is used:

REQUIRES_NEW
When the calling method is not in a transaction: Starts a new transaction.
When the calling method is in a transaction:  Suspends the existing transaction and creates a new one.

REQUIRED

When the calling method is not in a transaction: Starts a new transaction.
When the calling method is in a transaction:  Executes in existing transaction.

NEVER

When the calling method is not in a transaction: It will execute with no transaction.
When the calling method is in a transaction:  It will throw an exception.

NOT_SUPPORTED

When the calling method is not in a transaction: It will execute with no transaction
When the calling method is in a transaction: It will execute with no transaction(No exception will be thrown)  

SUPPORTS

When the calling method is not in a transaction: It will execute with no transaction.
When the calling method is in a transaction:  Executes in existing transaction.

MANDATORY

When the calling method is not in a transaction:  It will throw an exception.
When the calling method is in a transaction: Executes in existing transaction(Execution continues because the caller was already in a transaction).

How to unzip a .zip file with Zip4j

3 days ago I discovered a  cool easy to use java tool for working with zip files.
It is called Zip4j.

Have a look at this super simple example that will allow you to unzip a file into a given path in your computer:

 String source = "folder/source.zip";  
 String destination = "folder/source/";    
   try {  
     ZipFile zipFile = new ZipFile(source);  
     zipFile.extractAll(destination);  
   } catch (ZipException e) {  
     e.printStackTrace();  
   }  

Use this if the unzip file has a password:

 String source = "folder/source.zip";  
 String destination = "folder/source/";  
 String password = "password";  
 try {  
   ZipFile zipFile = new ZipFile(source);  
   if (zipFile.isEncrypted()) {  
     zipFile.setPassword(password);  
   }  
   zipFile.extractAll(destination);  
 } catch (ZipException e) {  
   e.printStackTrace();  
 }  

That was easy and cool.
Are you now thinking the same as I am thinking?...
Let's go brute force zip passwords!!! :P

Hahaha.... I am just joking don't do that, this is not a hacking blog( yet! :p )  I hope you enjoyed this post. Use Zip4j with care.