This article breaks down typical Scala development environment. We installed it in the previous section.
| What is it? | What does it do? | When and how to use it? | |
|---|---|---|---|
| Metals | Extention for VS Code. Language server for Scala. | It powers editing experience by error-checking, code formatting, autocompletion etc. Without it, the editor would not know how to assist you. Though it's not an IDE, it has rich IDE features. | After you install the extension, the editor will automatically use it. |
| Coursier | Scala development environment installer. Artefacts fetcher (or "dependency resolver") | It automatically installs applications and fetches other resources allowing Scala programs to run. | It is used from the terminal by the user to install Scala. |
| Sbt | Build automation tool. It stands for "simple build tool" | It builds runs Scala projects while interfacing with other applications. Consider it as a coordinator of those applications. | Go to the project via the terminal and type sbt. |
| Scalac | Scala compiler | It converts Scala code into Java bytecode so that the Java Virtual Machine (JVM) can run it. | Sbt launches Scalac when you compile your program. Compilation is done before running the program when you execute the run command from sbt. |
| JVM | Java Virtual Machine. Distinguish from the Java programming language | Runs Java bytecode. Note: first, Scalac compiles (converts) Scala code into Java bytecode, and then the JVM runs the bytecode. | Sbt launches JVM automatically (under the hood) when you run your program by sbt. |
| JDK | Java development kit (it includes the standard Java libraries, the Java compiler, a debugger and many more components) | It facilitates applications creation for the Java platform. | There is no need for the programmer to use the applications of the JDK manually. Sbt launches them automatically when you run your program. |
| Scalafmt | Scala code formatter | It keeps formatting (indentation, line breaks etc) compatible with conventions. | Metals automatically triggers Scalafmt. |
| Scala | Scala REPL and script runner | Evaluates expressions written in Scala. It is also used to run compiled scala programs - *.class files. | By the terminal when you want to run (e.g. test) easily some script without the overhead of setting up a project. Kind of "playground area". |
| Ammonite | Enhanced Scala REPL and script runner | Evaluates expressions written in Scala | Is launched from the terminal when you want to run easily (e.g. for testing purposes) some script without the overhead of setting up a project. Kind of "playground area". |