scala(四)Learn CH4 Programming in Scala from others

scala(4)Learn CH4 Programming in Scala from others
scala(4)Learn CH4 Programming in Scala from others

Classes and Objects
In scala, immutable var will not cost extra resource.
var acc = 0
var bcc = 0
There will be only 2 variables, acc and bcc, they all will equal to 0 value.

class ChecksumAccumulator {
  //private member in class
  private var sum = 0
  //return void function
  def add(b: Byte): Unit = {
    sum += b
  }
  //return int function, the last statement will be the return value
  def checksum(): Int = {
    return ~(sum & 0xFF) + 1
  }
}

There is no static function in Class. In scala, there is singleton, the only difference is that we change the keyword from class
to object.

object ASingleton{
  var a =0
}
ASingleton.a = 1

Basic Types and Operations
package com.sillycat.easyscala

object TestMain extends App {
    println("""Welcome to Ultamix 3000.
               Type "HELP" for help.""")

    println("""|Welcome to Ultamix 3000.
               |Type "HELP" for help.""".stripMargin)
}

There are 3 types of operators in scala, infix, prefix, postfix.

prefix: -2, !flag, +n,
infix:           
    println("string".indexOf('t'))
    println("string" indexOf "g")
    println("string".indexOf('s', 0))
postfix:
       println("string".toUpperCase())
    println("string" toUpperCase )
== means the content of the object, not like comparing the objects in JAVA.
println("string" == "string") //true

Functional Objects
package com.sillycat.easyscala

class Rational(n: Int, d: Int) {
  // check the parameter
  require(d != 0, "d can not be 0")

  private val g = gcd(n, d)

  // default is public
  val numer = n / g
  val denom = d / g

  def this(n: Int) = this(n, 1)

  //Override a method
  override def toString = n + "/" + d

  def ＋(that: Rational): Rational = {
    new Rational(n * that.denom + that.numer * d,
      d * that.denom)
  }

  def <(that: Rational): Boolean = {
    numer * that.denom < denom * that.numer
  }

  def max(that: Rational): Rational = {
    if (this < that) that else this
  }

  // greatest common divisor
  private def gcd(a: Int, b: Int): Int = {
    if (b == 0) a else gcd(b, a % b)
  }
}

  var r1 = new Rational(1, 3)
  var r3 = new Rational(3, 4)
  println(r1 < r3) //true
  println(r3 < r1) //false

references:
http://snowriver.org/blog/2011/03/19/programming-in-scala-ch4/
http://snowriver.org/blog/2011/03/19/programming-in-scala-ch5-basic-types-and-operations/
http://snowriver.org/blog/2011/03/19/programming-in-scala-ch6-functional-objects/