Table of Contents
What is Scala Main and what are its benefits
Scala is often used for server-side development, web applications, and other applications that need high performance and scalability. The phrase “Scala Main” refers to a programming language statement that can be used in Scala to set the main method of a program. The main method is then called when the program is executed. This main method will be explained in more detail below. Main issue with developing applications in Java:-
How to create a Scala Main project
Creating a Scala main project is done in the same way as any other project, however, it must implement the org.scalatest:org.scalatest._ package. The main class and its methods (if applicable) are defined in the application descriptor file, test-classes.scala and test-suite.scala respectively. The main class must be a public class and have a single method named main. This main method needs to have the signature:
public class MyMain extends Object {
public static main(args) {
// your code here! throw new java.lang.Exception(“Hello World!”); // No return from main method! } }() . . . . . . . . # end of file for test-classes.scala and test-suite.scala # begin # class TestApp extends ConsoleApp { # public void targetMain(String[] arguments) throws Throwable { } # } … end of file for test-classes.scala and test-suite.scala # end of file Project.scala
The above is a very simple example. The actual Main class can have as many methods as you like, and they can use as much or as little Scala code as you like. Below is an example of a more complex main method:
// File: main-method.scala class MyMain extends Object { private val LOGGER = LoggerFactory.getLogger(“MyMain”) def getData() = { LOGGER.info(“Hello World!”) } def main(args: Array [ String ]) { getData() } }
How to run a Scala Main program
The first thing we need to understand is why we use a main method in our Scala code. A main method is executed when the program runs. In most cases, a Scala application would have multiple classes and each class would then have many methods. We want our application to run as fast as possible, but we don’t want all of our methods to get executed when the program runs. So we use a main method to tell Scala which methods to execute. If a main method is not specified, the compiler will throw a Scala compilation error.
The easiest way to do this is to just add a main method that looks something like this:
1: 2: 3: 4: 5: 6: 7: 8: 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 import org . scala . lang . annotation . Intrinsic import org . scala . lang . annotation . tailrec def main ( args : Array [ String ] ) { @ tailrec def factorial ( n : Int , result : Int = 1 ) : Int = if ( n <= 1 ) result else factorial ( n - 1 , result * n ) println ( s "Factorial: $result" ) }
Examples of Scala Main programs
In this example, the main method will set the value of a Boolean flag named test. This value is then checked in a test that is part of our main class:
implicit val boolean_flag = new Boolean
val test = true
def pickle(char: Char): Int = { // implementation goes here }
class Person (name: String, age: Int) { val message: String } object Demo extends App { main(args : Array [ String ]) { println(“Hello, world!”); test.value } }
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