Archive for category streams

Refactoring large conditional method using method references

Some years ago I wrote junit-parameters, which is basically a custom JUnit test runner that make it possible to add parameters to JUnit 4 test methods.

Browsing its source code SonarLint pointed me a large conditional if/else method from the ParameterTypeConverterFactory class:

This method converts the method parameter to its specific type based on its Class object. As it is few lines long, it showed me a good opportunity to refactor this code a little bit with a more elegant solution. This project has unit tests, so I could start refactoring it in small steps and start over again whether I have made a mistake.

I started by defining a functional interface called ParameterConverter:

and I created an immutable map which maps each Class object to its associated ParameterConverter instance (making use of method references):

Then I refactored the original conditional method to get the ParameterConverter instance from the convertersByClass map and mapping to an Optional instance in case it didn’t exist.

After those refactorings, SonarLint stopped warning me. Below is the modified version of the original method with some helper methods:

The complete code can be found at my GitHub here.

This was the first change of breaking this complicated conditional method into a more readable one. It was safe to do so because after each change I could run my unit tests suite to assert I haven’t broken anything. The next refactoring could be towards a more object-oriented approach like Replace Conditional with Polymorphism.

What did you think about this refactoring? Have you ever had such a situation? Drop your comments here!

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Streams in JDK 8: The Good, the Bad, and the Ugly

Great session in JavaOne 2017 about Streams and lambdas introduced in JDK8.

The session shows many examples of Java code using forEach() with side effects and how to refactor them to a functional approach using streams and the Collectors API.

What are your experiences using Streams and lambdas in JDK 8? Are you correctly using the Collectors API?

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Java 8: Converting Optional Collection to the Streams API

Although Java 9 has already been released, this post is about converting an optional collection to the Streams API introduced in Java 8.

Suppose some person could have zero, one or more cars and it is represented by the Person class below (some code omitted).

Now we create a list of people and we want to get Mark’s cars.

How can we do that using the Streams API, since the getCars() method return an Optional?

One possibility is to filter people’s list by Mark’s name, filter the Optional if it is present or not and map its wrapped value (our cars list):

At this moment we reached the reason of this blog post. And how can we get all people’s cars? The idea here is to use the flatMap() operation unwrapping the Optional to the collection’s stream when it is present or getting an empty stream when it isn’t present:

We can do better and replace the above solution to be more functional using method references:

If you use IntelliJ IDEA as your favorite IDE, it has an inspection that helps replacing Optional.isPresent() with a functional expression:

P.S. In Java 9, the stream() method was added to the Optional API, so we can rewrite the above stream pipeline into the following one:

In case you are interested, this post on the IntelliJ IDEA blog has some good tips when working with Java 8.

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About the Kotlin programming language

Kotlin is a statically typed language which is fully interoperable with Java.

Recently my friend Andre showed me Kotlin‘s nice syntax and I considered giving it a try.

In the meantime, my friend Leonnardo sent me this nice link which helps migrating from Java to Kotlin easily.

Let’s compare some syntax from Java and Kotlin and see the differences. Suppose we have some employees and we want to group them by their departments.

In Java we create an Employee class, build some employees and use the Streams API to group them by their departments:

In Kotlin we create a data class Employee, build some employees and use the collection built-in groupBy method to group them by their departments:

As you can see, Kotlin has some syntactic sugar that makes it less verbose than Java.

If you haven’t considered trying Kotlin yet, I think it is worth giving it a try.

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