1.       Basic “Hello ” program of scala

 1.1. one way to write with main method

Scala is a general-purpose programming language providing support for both object-oriented programming and functional programming.

 def defines a method.

Compile: The scalac command compiles one (or more) Scala source file(s) and generates Java bytecode which can be executed on any standard JVM. The Scala compiler works similarly to javac, the Java compiler of the Java SDK.

> scalac HelloWorld.scala

Execute:  The scala command executes the generated bytecode with the appropriate options:

> scala HelloWorld

Example:

Following example illustrates how we can print “Hello Scala” with main method.

Save the file as − HellowWorld.scala.

HelloWorld.scala //File name

package runnerdev

object HelloWorld {

  def main(args: Array[String]) {

    println("Hello Scala")

  }

}

compile and run the above example as follows 

scala> scalac HelloWorld.scala

scala> scala HelloWorld

Output:

Hello Scala        

1.2. second way to write with out main method

 Another way to write that no need to define the main method but extends App

 The App trait can be used to quickly turn objects into executable programs. Here is an example:

  object Main extends App {

   println("Hello World: " + (args mkString ", "))

       }

Here, object Main inherits the main method of App.

args returns the current command line arguments as an array.

Example:

Following example illustrates how we can print “Hello Scala” with out main method.

Save the file as − HellowWorld.scala.

HelloWorld.scala //File name

package runnerdev

object HelloWorld extends App {

    println("Hello Scala")  

}

compile and run the above example as follows 

scala> scalac HelloWorld.scala

scala> scala HelloWorld

Output:

Hello Scala

Here is a simple "Hello, World!" program in Scala along with an explanation of each part:

scalaCopy code
object HelloWorld {
  def main(args: Array[String]): Unit = {
    println("Hello, World!")
  }
}

Explanation:

1. object HelloWorld: In Scala, the entry point of a program is an object. In this case, we define an object named "HelloWorld." Objects in Scala are singletons, meaning there is only one instance of the object in the entire application. This is where your program starts executing.

2. def main(args: Array[String]): Unit = { ... }: Within the "HelloWorld" object, we define a method named main. This is the entry point for your program, similar to the public static void main(String[] args) method in Java. The main method takes an array of strings args as its parameter, which can be used to pass command-line arguments to your program. Unit is similar to void in other programming languages and indicates that the method does not return any value.

3. println("Hello, World!"): Inside the main method, we use the println function to output the string "Hello, World!" to the standard output (usually the console). println is a predefined function in Scala used for printing text with a newline character at the end.

When you run this program, it will print "Hello, World!" to the console.

To run this program, follow these steps:

1. Make sure you have the Scala programming language installed on your system.

2. Save the code to a file named, for example, HelloWorld.scala.

3. Open your terminal or command prompt and navigate to the directory where you saved the file.

4. Compile the Scala code using the scalac compiler, which produces a bytecode file:

   Copy code
   scalac HelloWorld.scala
   

5. Run the program using the scala command:

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   scala HelloWorld
   

You should see the "Hello, World!" message printed to the console.

This simple program demonstrates the basic structure of a Scala program, with an object, a main method, and the use of a predefined function for output. Scala is concise and expressive syntax makes it a versatile language for various application types.