From Java Builders to Kotlin DSLs

From Java Builders to Kotlin DSLs

Android, Java, Kotlin, Tutorial
From Java Builders to Kotlin DSLs Introduction DSLs - Domain Specific Languages - are an ever trending topic in Kotlin circles. They allow us to flex some of the most exciting language features while accomplishing more readable and maintainable solutions in our code. Today I'd like to show you how to implement a certain kind of DSL - we're going to be wrapping an existing Java Builder in Kotlin. No doubt you've come across the builder pattern in Java before, for example if you're an Android developer, you must've used an AlertDialog.Builder, an OkHttpClient.Builder, or a Retrofit.Builder at some point. Wrapping a builder like this is a good exercise in just pure DSL design. All you have to worry about is designing the API you provide with your wrapper, since…
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Kotlin Nullability Features

Kotlin Nullability Features

Functional Programming, Java, Kotlin, Software Development, Teaching, Tutorial
Null-Safe Programming - The Kotlin Way Disclaimer: This ktor article was originally published in the Dzone Java Guide 2018, which can be downloaded here. In this article, we will review the problems that may be caused by null pointers and how to avoid them in Java. After that, the article demonstrates how Kotlin nullability features work and how they improve your code. As Java developers, we're very accustomed to NullPointerExceptions (NPE) that are thrown at the runtime of an application. This almost always happens unintentionally in consequence of a bug, which is based on unrecognized references to null. The null reference is often used to indicate absent values, which isn't obvious to the programmer in many cases. Although Java relies on strong static typing, it doesn't let you distinguish between…
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Run Kotlin Scripts (kts) from regular Kotlin Programs

Run Kotlin Scripts (kts) from regular Kotlin Programs

Gradle, Java, Kotlin, Software Development
Run Kotlin Scripts from Kotlin Programs This article presents a way to run Kotlin scripts from Kotlin programs in order to leverage the power of DSLs. Kotlin can be used as a scripting language. Simply write top-level executable code inside a file with .kts extension and run it with the kotlinc as described in the documentation. That's also the format of Gradle build files that are used in combination with the Gradle Kotlin DSL like this gradle.build.kts. Gradle shows a fantastic example of a domain specific language that can be written standalone in .kts files to be read by the gradle tool later on. When we try to find a way to do the same with custom DSLs (Tutorial can be found here), we first need to know how to…
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Kotlin Features I miss most in Java – Kotlin vs Java

Kotlin Features I miss most in Java – Kotlin vs Java

Functional Programming, Java, Kotlin, Software Development
Let's write an article that covers "Kotlin vs Java" topics - I want to tell you which Kotlin features I miss most when going back to Java. My Life as a Java Dev Although I'm a big supporter of the Kotlin programming language, I still do a lot of Java programming on a daily basis for my employer. Since I'm aware of the great functionalities of Kotlin, I'm often struggling with Java as it has some "pitfalls", requires additional boilerplate and misses many features. In this post, I'd like to describe which Kotlin features I miss most when coding in Java. new and Semicolon Ever since I'm doing Kotlin, there are two things I always forget when coding in Java: the new keyword for constructor invocations and the annoying ;…
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Create a DSL in Kotlin

Create a DSL in Kotlin

Functional Programming, Java, Kotlin, Software Development
Kotlin as a programming language provides some very powerful features, which allow the creation of custom internal Domain Specific Languages (DSL).  One of these features, I also wrote about on this blog, is called Function Literals with Receiver, others are the invoke convention or infix notation. In this article, I will show how to create a Kotlin DSL by introducing a library that exposes a DSL as its API. I've often been struggling with Java’s API when I had to set up SSL/TLS connections in scenarios where I e.g. needed to implement HTTPS communication. I always felt like wanting to write a little library that can support me with this task, hiding away all the difficulties and of course the boilerplate needed for it. (more…)
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Kotlin Operator Overloading – Working by Convention

Kotlin Operator Overloading – Working by Convention

Functional Programming, Kotlin, Software Development, Tutorial
Kotlin Operator Overloading and Conventions Introduction Kotlin supports a technique called conventions, everyone should be familiar with. For example, if you define a special method plus in your class, you can use the + operator by convention: Kotlin Operator Overloading. In this article, I want to show you which conventions you can use and I will also provide a few Kotlin code examples that demonstrate the concepts. (more…)
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Kotlin on the JVM – Bytecode Generation

Kotlin on the JVM – Bytecode Generation

Functional Programming, Kotlin, Software Development
Kotlin on the JVM - How can it provide so many features? Introduction What exactly is a "JVM language", what is Kotlin? Isn’t only Java meant to run on the JVM? Kotlin provides many features that aren’t available in Java such as proper function types, extension functions and data classes. How is this even possible? I’ve taken a deeper look at how Kotlin works under the hood and what "JVM language" actually means. We'll be having a look at Kotlin's bytecode generation. If you also thought about these things already, this article should bring some light into the darkness :) For a more detailed introduction to Kotlin’s features you can have a look at my Getting Started Guide. (more…)
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Kotlin Sealed Class – An Explanation

Kotlin Sealed Class – An Explanation

Kotlin, Software Development, Uncategorized
Today I came across the Kotlin Sealed Class which I had never heard of before. After some research, I found that this concept is nothing new and is also available in Scala for example. So, yet another Scala feature JetBrains considered relevant and suitable for Kotlin? I like that :) Read this post if you're interested in more Kotlin features. Actually, this is a quite simple feature, which I'm going to explain in the following. Kotlin Sealed Class - Feature Explanation A sealed class can be subclassed and may include abstract methods, which means that sealed classes are abstract implicitly, although the documentation doesn't clearly say so. To actually make a class "sealed" we have to put the sealed modifier before its name, as we can see here: sealed class MyClass Restriction The…
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Kotlin Generics and Variance (Compared to Java)

Kotlin Generics and Variance (Compared to Java)

Java, Kotlin, Software Development
This article covers the concepts of Generics and Variance in Kotlin and compares it to Java. Kotlin Generics differ from Java's in how users can define their type of variance. As opposed to Java, Kotlin allows defining variance on declaration-site, whereas Java only knows use-site variance. Kotlin Generics - What is Variance? Many programming languages support the concept of subtyping, which allows implementing hierarchies that represent relationships like "A Cat IS-An Animal". In Java, we can either use the extends keyword in order to change/expand behavior of an existing class (inheritance) or use implements to provide implementations for an interface. According to Liskov’s substitution principle, every instance of a class A can be substituted by instances of its subtype B. The word variance, often referred to in mathematics as well, is used…
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Java Oracle Certification

Java Oracle Certification

Certificate, Java, Software Development, Uncategorized
Java Oracle Certification - Should you consider it? I took the OCA SE 7 Programmer I Certification exam two years ago in 2015, which I passed successfully with a score of 86%. This year I will be taking the second exam of this certification path called OCP SE 7 Programmer II. In this post, I want to reflect why taking these kind of exams isn't a waste of time but can be a great advantage for you as a Java developer. Of course, being certified in whatever area will increase your chances of getting a better job because certificates represent some kind of guaranty of your skills to a company. No doubt about that. (more…)
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