Learn Java for Web Development

424 APPENDIX C: Introduction to Scala

From the command line, enter the following to open the interactive interpreter, shown in Figure C-1.

scala

Using the interactive interpreter you can run your first “Hello world” program by using the println
method.

scala> println("Hello world");

Hello world

To quit the interpreter, type exit.

scala> exit

Executing Scala Code as a Script

Another way to execute Scala code is to type it into a text file and save it with the extension .scala.
You can then execute that code by typing filename.scala. For instance, you can create a file named
hello.scala with “Hello world” in it.

println("Hello world")

To execute it, you specify the file name as a parameter to the Scala command-line tool.

scala hello.scala

Compiling Scala Code

You can also execute Scala code by first compiling it using the scalac command-line tool. Then the
code will need to be executed in the context of an application, so you will need to add an object with
a main() method (see Listing C-1).

Listing C-1. The “Hello world” Program

1. object HelloWorld {


2. def main(args: Array[String]) {


3. println("Hello, world")


4. }


5. }

Figure C-1. The Scala interactive interpreter