Return to chapter index

13 Packages and Imports

13.1 Putting code in packages

// In file packages/ex1/Ex1.scala

  package bobsrockets.navigation
  class Navigator


  package bobsrockets.navigation {
    class Navigator
  }


  package bobsrockets {
    package navigation {

      // In package bobsrockets.navigation
      class Navigator

      package tests {

        // In package bobsrockets.navigation.tests
        class NavigatorSuite
      }
    }
  }


// In file packages/ex4/Ex4.scala

  package bobsrockets {
    package navigation {
      class Navigator {
        // No need to say bobsrockets.navigation.StarMap
        val map = new StarMap
      }
      class StarMap
    }
    class Ship {
      // No need to say bobsrockets.navigation.Navigator
      val nav = new navigation.Navigator
    }
    package fleets {
      class Fleet {
        // No need to say bobsrockets.Ship
        def addShip() { new Ship }
      }
    }
  }


  package bobsrockets {
    class Ship
  }

  package bobsrockets.fleets {
    class Fleet {
      // Doesn't compile! Ship is not in scope.
      def addShip() { new Ship }
    }
  }


// In file packages/launch.scala

  // In file launch.scala
  package launch {
    class Booster3
  }

  // In file bobsrockets.scala
  package bobsrockets {
    package navigation {
      package launch {
        class Booster1
      }
      class MissionControl {
        val booster1 = new launch.Booster1
        val booster2 = new bobsrockets.launch.Booster2
        val booster3 = new _root_.launch.Booster3
      }
    }
    package launch {
      class Booster2
    }
  }


  

13.2 Concise access to related code

  package bobsrockets
  package fleets
  class Fleet {
    // Doesn't compile! Ship is not in scope.
    def addShip() { new Ship }
  }


  

13.3 Imports

// In file packages/Fruits.scala

  package bobsdelights

  abstract class Fruit(
    val name: String,
    val color: String
  )

  object Fruits {
    object Apple extends Fruit("apple", "red")
    object Orange extends Fruit("orange", "orange")
    object Pear extends Fruit("pear", "yellowish")
    val menu = List(Apple, Orange, Pear)
  }


// In file packages/Ex5.scala

  // easy access to Fruit
  import bobsdelights.Fruit

  // easy access to all members of bobsdelights
  import bobsdelights._

  // easy access to all members of Fruits
  import bobsdelights.Fruits._


// In file packages/Ex5.scala

  def showFruit(fruit: Fruit) {
    import fruit._
    println(name +"s are "+ color)
  }


// In file packages/Ex6.scala

  import java.util.regex

  class AStarB {
    // Accesses java.util.regex.Pattern
    val pat = regex.Pattern.compile("a*b")
  }


// In file packages/Ex7.scala

  import Notebooks._
  import Fruits.{Apple => _, _}


  

13.4 Implicit imports

  import java.lang._ // everything in the java.lang package
  import scala._     // everything in the scala package
  import Predef._    // everything in the Predef object


  

13.5 Access modifiers

// In file packages/Ex8.scala.err

  class Outer {
    class Inner {
      private def f() { println("f") }
      class InnerMost {
        f() // OK
      }
    }
    (new Inner).f() // error: f is not accessible
  }


// In file packages/Ex9.scala.err

  package p {
    class Super {
      protected def f() { println("f") }
    }
    class Sub extends Super {
      f()
    }
    class Other {
      (new Super).f()  // error: f is not accessible
    }
  }


// In file packages/ex10/Ex10.scala

 package bobsrockets

 package navigation {
   private[bobsrockets] class Navigator { 
     protected[navigation] def useStarChart() {}
     class LegOfJourney {
       private[Navigator] val distance = 100
     }
     private[this] var speed = 200
   }
 }
 package launch {
   import navigation._
   object Vehicle { 
     private[launch] val guide = new Navigator
   }
 }


  val other = new Navigator
  other.speed // this line would not compile


// In file packages/Rocket.scala

  class Rocket {
    import Rocket.fuel
    private def canGoHomeAgain = fuel > 20
  }

  object Rocket {
    private def fuel = 10
    def chooseStrategy(rocket: Rocket) {
      if (rocket.canGoHomeAgain)
        goHome()
      else
        pickAStar()
    }
    def goHome() {}
    def pickAStar() {}
  }


  

13.6 Package objects

// In file packages/package.scala

  // In file bobsdelights/package.scala
  package object bobsdelights {
    def showFruit(fruit: Fruit) {
      import fruit._
      println(name +"s are "+ color)
    }
  }

  // In file PrintMenu.scala
  package printmenu
  import bobsdelights.Fruits
  import bobsdelights.showFruit

  object PrintMenu {
    def main(args: Array[String]) {
      for (fruit <- Fruits.menu) {
        showFruit(fruit)
      }
    }
  }


  

13.7 Conclusion