Kotlin Online Editor
Toni Jarels
Write, Run & Share Kotlin code online using OneCompiler's Kotlin online compiler for free. It's one of the robust, feature-rich online compilers for Kotlin language. Getting started with the OneCompiler's Kotlin editor is easy and fast. The editor shows sample boilerplate code when you choose language as Kotlin and start coding.
If you are starting with Kotlin, you can learn the language by reading the reference documentation, following the online Kotlin Koans tutorial or just using Spring Framework reference documentation which now provides code samples in Kotlin.
Spring Kotlin support is documented in the Spring Framework and Spring Boot reference documentation. If you need help, search or ask questions with the spring and kotlin tags on StackOverflow or come discuss in the #spring channel of Kotlin Slack.
Visit and choose the Kotlin language. Gradle is the most commonly used build tool in Kotlin, and it provides a Kotlin DSL which is used by default when generating a Kotlin project, so this is the recommended choice. But you can also use Maven if you are more comfortable with it. Notice that you can use !language=kotlin&type=gradle-project-kotlin to have Kotlin and Gradle selected by default.
In addition to the obvious Kotlin Gradle plugin, the default configuration declares the kotlin-spring plugin which automatically opens classes and methods (unlike in Java, the default qualifier is final in Kotlin) annotated or meta-annotated with Spring annotations. This is useful to be able to create @Configuration or @Transactional beans without having to add the open qualifier required by CGLIB proxies for example.
In order to be able to use Kotlin non-nullable properties with JPA, Kotlin JPA plugin is also enabled. It generates no-arg constructors for any class annotated with @Entity, @MappedSuperclass or @Embeddable.
Although Java does not allow one to express null-safety in its type-system, Spring Framework provides null-safety of the whole Spring Framework API via tooling-friendly annotations declared in the org.springframework.lang package. By default, types from Java APIs used in Kotlin are recognized as platform types for which null-checks are relaxed. Kotlin support for JSR 305 annotations + Spring nullability annotations provide null-safety for the whole Spring Framework API to Kotlin developers, with the advantage of dealing with null related issues at compile time.
jackson-module-kotlin adds support for serialization/deserialization of Kotlin classes and data classes (single constructor classes can be used automatically, and those with secondary constructors or static factories are also supported)
In addition to the obvious Kotlin Maven plugin, the default configuration declares the kotlin-spring plugin which automatically opens classes and methods (unlike in Java, the default qualifier is final in Kotlin) annotated or meta-annotated with Spring annotations. This is useful to be able to create @Configuration or @Transactional beans without having to add the open qualifier required by CGLIB proxies for example.
Compared to Java, you can notice the lack of semicolons, the lack of brackets on empty class (you can add some if you need to declare beans via @Bean annotation) and the use of runApplication top level function. runApplication(*args) is Kotlin idiomatic alternative to SpringApplication.run(BlogApplication::class.java, *args) and can be used to customize the application with following syntax.
Notice that we are using here a Kotlin extension that allows to add Kotlin functions or operators to existing Spring types. Here we import the org.springframework.ui.set extension function in order to be able to write model["title"] = "Blog" instead of model.addAttribute("title", "Blog"). The Spring Framework KDoc API lists all the Kotlin extensions provided to enrich the Java API.
JUnit 5 now used by default in Spring Boot provides various features very handy with Kotlin, including autowiring of constructor/method parameters which allows to use non-nullable val properties and the possibility to use @BeforeAll/@AfterAll on regular non-static methods.
Sometimes you need to execute a method before or after all tests of a given class. Like Junit 4, JUnit 5 requires by default these methods to be static (which translates to companion object in Kotlin, which is quite verbose and not straightforward) because test classes are instantiated one time per test.
But Junit 5 allows you to change this default behavior and instantiate test classes one time per class. This can be done in various ways, here we will use a property file to change the default behavior for the whole project:
Instead of using util classes with abstract methods like in Java, it is usual in Kotlin to provide such functionalities via Kotlin extensions. Here we are going to add a format() function to the existing LocalDateTime type in order to generate text with the English date format.
Notice that we are using here our String.toSlug() extension to provide a default argument to the slug parameter of Article constructor. Optional parameters with default values are defined at the last position in order to make it possible to omit them when using positional arguments (Kotlin also supports named arguments). Notice that in Kotlin it is not unusual to group concise class declarations in the same file.
We update the HtmlController in order to render blog and article pages with the formatted date. ArticleRepository and MarkdownConverter constructor parameters will be automatically autowired since HtmlController has a single constructor (implicit @Autowired).
We have now finished to build this sample Kotlin blog application. The source code is available on Github. You can also have a look to Spring Framework and Spring Boot reference documentation if you need more details on specific features.
I tried Codeanywhere, and it was awesome. All I had to click was LAMP Stack, and my environment was ready to go. I really liked that phpMyAdmin was also all ready to go. I have been using it for over a month now and its been great (its a little buggy at times, but it works for my purposes).
I am not familiar with those IDEs but I get the impression that the website used by them were remote, as in not your local system. Something that is highly predominant is to have a server in your local system that you use.
Of those, I found all but IntelliJ IDEA to have steep learning curves and overwhelming numbers of features that helped push me to turn away from them. To be fair, the struggles I had could very well have been because I was too much a newbie at the time and maybe I gave up on them too soon.
Also, my history and use may be important. I used plain notepad as my text editor for many years and even now I feel comfortable using Notepad++ I use the IDE for project management and versioning (GitHub)
For the setup that is a little harder, again all depending on language. But you can easily run containers, virtual machines or even local setup, you just need to get over the initial few hours setting it up, and from that point it will feel seamless.
I would recommend installing LAMP on your computer because it is then possible to not only have a local copy of the online database content but also all the PHP, HTML, CSS, JavaScript, etc, files necessary to render the online website.
I have tried many IDEs and been very disappointed and always revert back to a simple text editor. There are numerous excellent validation tools which can ensure the resultant web pages conform and render on all platforms.
One of the biggest mistakes beginners do while learning a new technology is local setup. Many people procrastinate a lot at this step. And the reason for this is you don't know how things work. You need to get some basic understanding of that tech. So you can use these online playgrounds that have all things set up for you so that you can start learning right away. In this blog, I am going to share some amazing online playgrounds for various techs and also some production level online IDEs. (Bookmark or save to refer later.)
StackBlitz is another amazing online IDE for building full-stack applications. It has support for most of the frontend and backend(NextJs, Graphql, NodeJs starter and HTTP server) frameworks and libraries.
CodePen is an ultimate online playground for front-end devs and designers. You can create an art called Pen and share it with the internet. CodePen is more of a community than an editor. Get inspiration from creations by devs and designers across the world.
RunKit is a notebook-style NodeJs playground. It's like the jupyter-notebook but for NodeJs. To use runkit, all you have to do is insert a script tag in your code. You can also explore notebooks created by the runkit community.
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