add answers to exercise 1-4 chapter 5

src/main/scala/org/learningconcurrency/exercises/ch5/Ex2.scala

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+package org.learningconcurrency.exercises.ch5
+
+object Ex2 {
+
+}

src/main/scala/org/learningconcurrency/exercises/ch5/Ex3.scala

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+package org.learningconcurrency.exercises.ch5
+
+object Ex3 {
+
+}

src/main/scala/org/learningconcurrency/exercises/ch5/ex1.scala

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+package org.learningconcurrency
+package exercises
+package ch5
+
+/**
+ * Measure the average running time of allocating a simple object on the JVM.
+ */
+
+object Ex1 extends App {
+
+  object Timed {
+
+    @volatile 
+    var dummy: Any = _
+
+    def buildObjects(count:Int) = {
+      var i = 0
+      val start = System.nanoTime
+      while (i < count) {
+        dummy = new Object
+        i += 1
+      }
+      (System.nanoTime - start)/count.toDouble
+    }
+
+  }
+
+  var i = 0
+  var summ = 0D
+
+  var timePrev = 0D
+  while (i < 30) {
+
+    val time = Timed.buildObjects(10000000)
+    val e = Math.abs(time - timePrev)/time*100
+
+    //check steady state
+    if (e < 10) {
+      i += 1
+      summ += time
+    } else {
+      i = 0
+      summ = time
+    }
+
+    timePrev = time
+    log(s"time = ${time.toString} e = ${Math.round(e)}, i = $i")
+
+  }
+
+  log("----------------------------------------------------")
+  log(s"avg = ${summ/(i+1)} nanoseconds")
+
+}

src/main/scala/org/learningconcurrency/exercises/ch5/ex4.scala

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+package org.learningconcurrency
+package exercises
+package ch5
+
+import javafx.scene.layout.HBox
+
+import scalafx.Includes._
+import scalafx.application.JFXApp
+import scalafx.application.JFXApp.PrimaryStage
+import scalafx.geometry.Insets
+import scalafx.scene.Scene
+import scalafx.scene.control._
+import scalafx.scene.layout.{Pane, VBox}
+import scalafx.scene.paint.Color
+import scalafx.scene.shape.Rectangle
+
+object Ex4 extends JFXApp {
+
+  /**
+   * Implement a program that simulates a cellular automaton in parallel.
+   */
+
+  val maxX = 40
+  val maxY = 40
+
+  case class Cell(state: Boolean, index: Int, neighbors: Seq[Int])
+
+  def index(i: Int, j: Int) = i + j * maxX
+
+  def findNeighbors(x: Int, y: Int) = {
+    for {
+      i <- x - 1 to x + 1
+      j <- y - 1 to y + 1
+      if i > -1 && i < maxX && j > -1 && j < maxY && ((i != x) || (j != x))
+    } yield index(i, j)
+  }
+
+  def checkInitialState(x: Int, y: Int) = (x == maxX / 2 - 1 || x == maxX / 2 + 1) && y == maxY / 2
+
+  def initialize: IndexedSeq[Cell] = {
+    (
+      for {
+        x <- 0 until maxX
+        y <- 0 until maxY
+      } yield (x, y)
+      ).map {
+      case (x, y) => Cell(
+        state = checkInitialState(x,y),
+        index = index(x, y),
+        neighbors = findNeighbors(x, y)
+      )
+    }
+  }
+
+  def countNeighbors(cell: Cell, cells: Seq[Cell]) =
+    cell.neighbors.count((i) => cells(i).state)
+
+  def defState(countNeighbors: Int) = {
+    (countNeighbors == 2) || (countNeighbors == 3)
+  }
+
+  def next(cells: Seq[Cell]) = {
+    cells.par.map(
+      (cell) => cell.copy(state = defState(countNeighbors(cell, cells)))).toIndexedSeq
+  }
+
+  //Test App
+
+  var cells = List(initialize)
+
+  val cellAreaWidth = 400
+  val cellAreaHeight = 400
+
+  val rectWidth = cellAreaWidth / maxX
+  val rectHeight = cellAreaHeight / maxY
+
+  def buildRectangles = (
+    for {
+      y <- 0 until maxY
+      x <- 0 until maxX
+    } yield (x, y)).
+    map {
+    case (posX, posY) => new Rectangle() {
+      x = posX * rectWidth
+      y = posY * rectHeight
+      width = rectWidth
+      height = rectHeight
+      fill = Color.GRAY
+    }
+  }.toArray
+
+
+  val rectangles = buildRectangles
+
+  val cellsPane = new Pane {
+    maxWidth = cellAreaWidth
+    maxHeight = cellAreaHeight
+  }
+  rectangles.foreach(cellsPane.children.add(_))
+
+  def drawCells = cells.head.foreach((c) => rectangles(c.index).setFill(if (c.state) Color.RED else Color.WHITE))
+
+  val nextButton = new Button() {
+    text = "=>"
+    onAction = handle {
+      cells = next(cells.head) :: cells
+      drawCells
+    }
+  }
+
+  val prevButton = new Button() {
+    text = "<="
+    onAction = handle {
+      cells = cells match {
+        case h :: Nil => cells
+        case h :: t => t
+      }
+      drawCells
+    }
+  }
+
+  val hbox = new HBox()
+  hbox.children.add(prevButton)
+  hbox.children.add(nextButton)
+
+
+  val vbox = new VBox {
+    padding = Insets(20)
+    spacing = 10
+  }
+
+  vbox.children.add(hbox)
+  vbox.children.add(cellsPane)
+
+  stage = new PrimaryStage {
+    title.value = "Ch5 Ex4"
+    scene = new Scene {
+      content = vbox
+    }
+  }
+
+  stage.sizeToScene()
+
+  drawCells
+
+}