可重新赋值的变量和属性
对可重新赋值的变量执行两种操作：获取它的值或者设定为新的值。

//定义公开变量，公开变量扩展为getter和setter方法
object Ex4 {
  class Time {
    var hour = 12
    var minute = 0
  }

  def main(args: Array[String]) {
    val time = new Time
    println("time.hour [" + (time.hour) + "]")
    println("time.minute [" + (time.minute) + "]")

    time.hour = 13
    time.minute = 14
    println("time.hour [" + (time.hour) + "]")
    println("time.minute [" + (time.minute) + "]")
  }
}

//直接定义getter和setter方法
object Ex6 {
  class Time {
  
    private[this] var h = 12
    private[this] var m = 12
  
    def hour: Int = h
    def hour_= (x: Int) {
      require(0 <= x && x < 24)
      h = x
    }
  
    def minute = m
    def minute_= (x: Int) {
      require(0 <= x && x < 60)
      m = x
    }
  } 

  def main(args: Array[String]) {
    val time = new Time
    println("time.hour [" + (time.hour) + "]")
    println("time.minute [" + (time.minute) + "]")

    time.hour = 13
    time.minute = 14
    println("time.hour [" + (time.hour) + "]")
    println("time.minute [" + (time.minute) + "]")

    try {
      time.minute = 75
    } catch {
      case ex: IllegalArgumentException => println("caught exception")
    }
  }
}

//定义不带关联字段的getter和setter
object Ex7 {
  class Thermometer {
  
    var celsius: Float = _ //初始化变量设定为缺省值
  
    def fahrenheit = celsius * 9 / 5 + 32
    def fahrenheit_= (f: Float) {
      celsius = (f - 32) * 5 / 9
    }
    override def toString = fahrenheit +"F/"+ celsius +"C"
  }

  def main(args: Array[String]) {
    val t = new Thermometer

    t.celsius = 100
    println("t [" + (t) + "]")

    t.fahrenheit = -40
    println("t [" + (t) + "]")
  }
}
val t=new Ex7.Thermometer
//t: Ex7.Thermometer = 32.0F/0.0C
t.celsius
//res20: Float = 0.0
t.celsius=100
//t.celsius: Float = 100.0
println("t [" + (t) + "]")
//t [212.0F/100.0C]

离散事件模拟

//数字电路模拟

object Simulator2 {

  abstract class BasicCircuitSimulation extends Simulation {

    def InverterDelay: Int  //反转器，输出反转信号
    def AndGateDelay: Int //与门，输出其输入信号的合取值
    def OrGateDelay: Int //或门，输出其输入信号的析取值

//wire 线路
    class Wire {
    
      private var sigVal = false
      private var actions: List[Action] = List()
    
      def getSignal = sigVal
    
      def setSignal(s: Boolean) = 
        if (s != sigVal) {
          sigVal = s
          actions foreach (_ ()) 
        }
    
      def addAction(a: Action) = {
        actions = a :: actions
        a()
      }
    }

    def inverter(input: Wire, output: Wire) = {
      def invertAction() {
        val inputSig = input.getSignal
        afterDelay(InverterDelay) {
          output setSignal !inputSig 
        }
      }
      input addAction invertAction
    }

    def andGate(a1: Wire, a2: Wire, output: Wire) = {
      def andAction() = {
        val a1Sig = a1.getSignal
        val a2Sig = a2.getSignal
        afterDelay(AndGateDelay) {
          output setSignal (a1Sig & a2Sig) 
        }
      }
      a1 addAction andAction
      a2 addAction andAction
    }

    def orGate(o1: Wire, o2: Wire, output: Wire) {
      def orAction() {
        val o1Sig = o1.getSignal
        val o2Sig = o2.getSignal
        afterDelay(OrGateDelay) {
          output setSignal (o1Sig | o2Sig)
        }
      }
      o1 addAction orAction
      o2 addAction orAction
    }

    def probe(name: String, wire: Wire) {
      def probeAction() {
        println(name +" "+ currentTime +
            " new-value = "+ wire.getSignal)
      }
      wire addAction probeAction
    }
  }
//SimulationAPI
//私有变量和公开访问方法的组合可以用来保证当前时间不背Simulation类外部的方法改变。
  abstract class Simulation {

    type Action = () => Unit

    case class WorkItem(time: Int, action: Action)

    private var curtime: Int = 0
    def currentTime: Int = curtime

    private var agenda: List[WorkItem] = List()

    private def insert(ag: List[WorkItem],
        item: WorkItem): List[WorkItem] = {

      if (ag.isEmpty || item.time < ag.head.time) item :: ag
      else ag.head :: insert(ag.tail, item)
    }

    def afterDelay(delay: Int)(block: => Unit) {
      val item = WorkItem(currentTime + delay, () => block)
      agenda = insert(agenda, item)
    }

    private def next() {
      (agenda: @unchecked) match {
        case item :: rest => 
          agenda = rest 
          curtime = item.time
          item.action()
      }
    }

    def run() {
      afterDelay(0) {
        println("*** simulation started, time = "+
            currentTime +" ***")
      }
      while (!agenda.isEmpty) next()
    }
  }


  abstract class CircuitSimulation
    extends BasicCircuitSimulation {
//半加法电路
    def halfAdder(a: Wire, b: Wire, s: Wire, c: Wire) {
      val d, e = new Wire
      orGate(a, b, d)
      andGate(a, b, c)
      inverter(c, e)
      andGate(d, e, s)
    }
//全加法器
    def fullAdder(a: Wire, b: Wire, cin: Wire,
        sum: Wire, cout: Wire) {
    
      val s, c1, c2 = new Wire
      halfAdder(a, cin, s, c1)
      halfAdder(b, s, sum, c2)
      orGate(c1, c2, cout)
    }
  }
}

object MySimulation2 extends Simulator2.CircuitSimulation {
           def InverterDelay = 1
           def AndGateDelay = 3
           def OrGateDelay = 5

  def main(args: Array[String]) {
    val input1, input2, sum, carry = new Wire

    probe("sum", sum)
    probe("carry", carry)
    halfAdder(input1, input2, sum, carry)

    input1 setSignal true
    run()

    input2 setSignal true
    run()
  }
}