Changing Java versions

You can use Scala CLI to test your code compatibility with various versions of java, with a key point being that manual installation of a JDK/SDK is not required(!). Scala CLI automatically downloads the Java version you specify.

As an example, the following snippet uses the new method Files.writeString from Java 11:

import java.nio.file.Files
import java.nio.file.Paths

object Main extends App {
  val dest = Files.createTempDirectory("scala-cli-demo").resolve("hello.txt")
  val filePath = Files.writeString(dest, "Hello from ScalaCli")
  val fileContent: String = Files.readString(filePath)
  println(fileContent)
}

To use Java 11 to run this application, pass the following --jvm option to the Scala CLI command:

scala-cli --jvm temurin:11 Main.scala

To attempt to compile the application with Java 8, change the value of the --jvm parameter:

scala-cli --jvm 8 Main.scala
# In this case, it raises an error because the `Files.writeString` and `Files.readString` methods are not available in java 8
#
# [error] ./Main.scala:6:18
# [error] value writeString is not a member of object java.nio.file.Files
# [error]   val filePath = Files.writeString(dest, "Hello from ScalaCli")
# [error]                  ^^^^^^^^^^^^^^^^^
# [error] ./Main.scala:7:29
# [error] value readString is not a member of object java.nio.file.Files
# [error]   val fileContent: String = Files.readString(filePath)
# [error]                             ^^^^^^^^^^^^^^^^