COE 808 Tue. March 2,  2010       Scala                                  Page 1 of 3
             COE808 Lecture Notes Tuesday March 2, 2010
             Topics
                  •  Scala
             Scala
             Scala goals
             Ref: Scala overview
                 •    Both object-oriented and functional programming paradigms supported.
                 •    Scalable (from small to large software systems) component re-use a major goal.
                 •    Works well with Java and C#.
                 •    Uniformity: every value is an object (no distinction between primitive and reference data 
                      types as in Java) and every operation is a method call (similar to scheme)
                 •    Every class inherits from Scala.Any.  Value classes (roughly like Java's primitives) 
                      inherit from Scala.AnyVal and all reference classes inherit from 
                      Scala.AnyRef.
                 •    Equality (==) works like .equals(Object o) in Java; the scala .eq() method 
                      (which cannot be overridden) checks for true identity in the rare cases when this is  
                      needed (eg. Implementing hash tables).
                 •    Operators (like +) are methods.  Indeed an identifier between two variables is treated as 
                      a method call. Thus val a = 3; val b = 4; println(a.+(b)); is how 
                      a+b is interpreted.  Similarly, “abcd”.contains(“bc”) (which returns True) can 
                      be written as “abcd” contains “bc”.
                 •
             Examples
             object PrintOptions {
                 def main(args: Array[String]): Unit = {
                     System.out.println("Options selected:")
                         for (arg <- args)
                             if (arg.startsWith("-"))
                                 System.out.println(" "+arg.substring(1))
                     }
             }
             object PrintArgs { 
             COE 808 Tue. March 2,  2010       Scala                                  Page 2 of 3
                 def main(args: Array[String]): Unit = {
              //Anonymous function (params => body of anonymous function)
                     args.foreach(arg => println(arg))
                 }           
             }      
             class Celsius {
                 private var d: Int = 0
                 def degree: Int = d
                 def degree_=(x: Int): Unit = if (x >= -273) d = x
             }
             object Timer {
                 var i = 0
                 def oncePerSec(callback: () => Unit) {
                     while(true) {callback(); Thread sleep 1000 }
                 }
                 def timeFlies() {
                     println("Time flies like an arrow " + i)
                     i += 1
                 }
                 def main(args: Array[String]) {
                     oncePerSec(timeFlies)
                 }
             }
             class Complex(real: Double, imag: Double) {
                 def re = real
                 def im = imag
                 override def toString() =
                     "" + real + (if (imag < 0) "" else "+") + imag + "i"
                 def add(z: Complex): Complex =
                     new Complex(this.re + z.re, im + z.im)
                //OR define the + operator
                 def +(z: Complex) =
                     new Complex(this.re + z.re, im + z.im)
                 def *(z: Complex) =
                     new Complex(re * z.re - im*z.im, im*z.re + z.im*re)
             }
             import java.util.{Date, Locale}
             import java.text.DateFormat
             import java.text.DateFormat._
             object FrenchDate {
             COE 808 Tue. March 2,  2010       Scala                                  Page 3 of 3
                 def main(args: Array[String]) {
                     val now = new Date
                     val df = getDateInstance(LONG, Locale.FRANCE)
                     println(df format now)
                 }
             }