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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)

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

scala-cli --jvm adopt: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.createTempFile` method is not available in java 8
# Exception in thread main: java.lang.Exception: java.lang.NoSuchMethodError: java.nio.file.Files.writeString(Ljava/nio/file/Path;Ljava/lang/CharSequence;[Ljava/nio/file/OpenOption;)Ljava/nio/file/Path;
# at method print in modules/runner/src/main/scala-3-stable/scala/cli/runner/Stacktrace.scala:12 inside runner_3.jar
# at method printException in modules/runner/src/main/scala/scala/cli/runner/StackTracePrinter.scala:91 inside runner_3.jar
# at method main in modules/runner/src/main/scala/scala/cli/runner/Runner.scala:22 inside runner_3.jar