FirstSteps03Classes.sc

package day01session01.first_steps.solution

/*
 * This file is part of the "Scala Hack Session".
 *
 * Scala Hack Session is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Scala Hack Session is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Scala Hack Session.  If not, see <http://www.gnu.org/licenses/>.
 *
 * =================================================================================
 *
 */
object FirstSteps03Classes {

  //class definitions
  //inside the class define:
  // - dateFormat and
  // - constructionTime
  //like in the previous exercise
  class ScalaFun {
    //unlike Java imports can also be defined within a class or function
    import java.text.SimpleDateFormat

    private val alive = true
    //define variables for dateFormat and constructionTime here
    var constructionTime = System.currentTimeMillis()
    val dateFormat = new SimpleDateFormat("dd:MM:yyyy HH:mm:ss:SSS")

    //Constructors with params are defined using "def this(params)".
    //The first call must always be the primary constructor "this()"
    def this(constructionTime: Long) = {
      this()
      this.constructionTime = constructionTime + 1000
    }
  }

  //now instantiate the class and have a look at the output
  //note: in Scala for default constructors a "new MyClass" without brackets is just fine
  //in Scala
  val instance = new ScalaFun                     //> instance  : day01session01.first_steps.solution.FirstSteps03Classes.ScalaFu
                                                  //| n = day01session01.first_steps.solution.FirstSteps03Classes$ScalaFun@b27868
                                                  //| b

  //do a println using the instance' dateFormat and constructionTime
  println(instance.dateFormat.format(instance.constructionTime))
                                                  //> 19:02:2014 17:41:11:796

  //Example taken from: http://www.artima.com/pins1ed/case-classes-and-pattern-matching.html
  //Case classes: adding the "case" modifier to a class lets the compiler add some syntactic conveniences to the class:
  //- a factory method making instantiation easier: "CaseClass(param)" instead of "new CaseClass(param)"
  //- all arguments get a "val" prefix and can be publicly accessed as fields
  //- adds "natural" implementations of toString, hashCode and equals.
  //case classes are always structually (deep) compared (using "equals" resp. "==")
  abstract class Expr
  case class Var(name: String) extends Expr
  case class Number(num: Double) extends Expr
  case class VarNumber(num: Double, name: String) extends Expr

  //instantiate Number and Var and print them out
  val num = Number(2.5)                           //> num  : day01session01.first_steps.solution.FirstSteps03Classes.Number = Num
                                                  //| ber(2.5)
  val variable = VarNumber(2.5, "varNum")         //> variable  : day01session01.first_steps.solution.FirstSteps03Classes.VarNumb
                                                  //| er = VarNumber(2.5,varNum)
  //print
  println(s"$num and $variable")                  //> Number(2.5) and VarNumber(2.5,varNum)
  //another convenience is the copy function of case classes where you can call caseClass.copy(param1Value, param2Value, ...)
  //the copy function requires at least one param, are others will then be copied
  //in case a specific param should be overridden then use: copy(param3=value, param2=value)
  val varNum1 = VarNumber(2.4, "varNum1")         //> varNum1  : day01session01.first_steps.solution.FirstSteps03Classes.VarNumbe
                                                  //| r = VarNumber(2.4,varNum1)
  //copy with first value changed
  val varNum2 = varNum1.copy(2.5)                 //> varNum2  : day01session01.first_steps.solution.FirstSteps03Classes.VarNumbe
                                                  //| r = VarNumber(2.5,varNum1)
  //call copy with only the second value changed
  val varNum3 = varNum1.copy(name="varNum2")      //> varNum3  : day01session01.first_steps.solution.FirstSteps03Classes.VarNumbe
                                                  //| r = VarNumber(2.4,varNum2)
  
  case class Super
  //try to define a case class extending from super
  //this will break. have a look at the error message
  //case class Child extends Super
}