Kotlin Playground

A quick and easy way to experiment with Kotlin online without having to install anything. Just change the code and run it!

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Kotlin to Java

Code targeting the Java platform supports all language features and APIs the JDK provides.


      import java.util.Arrays
      import java.util.stream.Collectors

      fun main(args: Array<String>) {
        // How one might do it with plain Java APIs
        val javaWords = Arrays.asList("hello", "world", "in", "java")
        System.out.println(javaWords.stream().collect(Collectors.joining(" ")))

        // How one might do the same with Kotlin APIs
        val kotlinWords = listOf("hello", "world", "in", "kotlin")
        println(kotlinWords.joinToString(separator = " "))
      }

Kotlin to JavaScript

Code targeting web browsers does not support APIs provided by the JDK unless they've been re-implemented for the JavaScript platform. But any JavaScript API can be called. See here and here for more information.


      fun main(args: Array<String>) {
        alert("Hello World!")
        console.log("Hello World!")
      }

      // Serves sort of like a header declaration. The keyword 'external' tells Kotlin that the
      // actual implementation is provided by the developer or the platform. In this case it's
      // Window.alert().
      external fun alert(message: String)

      // Or Window.console. Execute this code snippet and have a look in your web browser's
      // script console. The type 'dynamic' is only available for the JavaScript platform and
      // basically disables any type check for this value.
      external val console: dynamic;