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

Static members (methods or fields) do not exist in Scala. Rather than defining static members, the Scala programmer declares these members in singleton objects.

To compile the example, we use scalac, the Scala compiler.

One of Scala’s strengths is that it makes it very easy to interact with Java code. All classes from the java.lang package are imported by default, while others need to be imported explicitly.

import java.util.{Date, Locale}
import java.text.DateFormat._

object FrenchDate {
  def main(args: Array[String]): Unit = {
    val now = new Date
    val df = getDateInstance(LONG, Locale.FRANCE)
    println(df format now)
  }
}

This last line shows an interesting property of Scala’s syntax. Methods taking one argument can be used with an infix syntax.

df format now

df.format(now)

Scala is a pure object-oriented language in the sense that everything is an object, including numbers or functions.

Classes in Scala are declared using a syntax which is close to Java’s syntax. One important difference is that classes in Scala can have parameters.

class Complex(real: Double, imaginary: Double) {
  def re() = real
  def im() = imaginary
}


//a better way
class Complex(real: Double, imaginary: Double) {
  def re = real
  def im = imaginary
}

class Complex(real: Double, imaginary: Double) {
  def re = real
  def im = imaginary
  override def toString() =
    "" + re + (if (im >= 0) "+" else "") + im + "i"
}

type Environment = String => Int