Scala class and arguments

原创转载请注明出处：http://agilestyle.iteye.com/blog/2333082

Class

package org.fool.scala.classes

class Giraffe

class Bear

class Hippo

object Animals extends App {
  val giraffe1 = new Giraffe
  val giraffe2 = new Giraffe

  val bear = new Bear
  val hippo = new Hippo

  println(giraffe1)
  println(giraffe2)
  println(bear)
  println(hippo)
}

Console Output

Class Arguments

package org.fool.scala.classes

class ClassArg1(a: Int) {
  println(f)

  def f(): Int = a * 10
}

/*
 如果希望a在类体的外部也是可见的，那么需要将其定义为参数列表中的var或val
 */
class ClassArg2(var a: Int)

class ClassArg3(val a: Int)

object ClassArg extends App {
  val c1 = new ClassArg1(10)
  // c1.a // error

  val c2 = new ClassArg2(20)
  val c3 = new ClassArg3(30)

  println(c2.a)
  println(c3.a)

  c2.a = 40
  // c3.a = 50 // error
  println(c2.a)
  println(c3.a)
}

Console Output

Multiple Class Arguments

package org.fool.scala.classes

class Sum3(a1: Int, a2: Int, a3: Int) {
  def result(): Int = a1 + a2 + a3
}

object MultipleClassArgs extends App {
  println(new Sum3(1, 2, 3).result())
}

Console Output

Variable Class Arguments

package org.fool.scala.classes

class Sum(args: Int*) {
  def result(): Int = {
    var total = 0
    for (n <- args) {
      total += n
    }
    total
  }
}

object VariableClassArgs extends App {
  println(new Sum(1, 3, 5).result())
  println(new Sum(1, 3, 5, 7, 9).result())
}

Console Output

Named Arguments

package org.fool.scala.classes

class Color(red: Int, blue: Int, green: Int)

object NamedArgs extends App {
  new Color(red = 1, blue = 2, green = 3)
  new Color(1, 2, green = 3)
  new Color(1, blue = 2, 3)
}

Named And Default Arguments

package org.fool.scala.classes

class Color2(red: Int = 100, blue: Int = 100, green: Int = 100)

object NamedAndDefaultArgs extends App {
  new Color2(1)
  new Color2(1, 2)
  new Color2(blue = 2)
  new Color2(red = 1, green = 3)
}

Note

Named and default arguments currently have an idiosyncrasy when combined with a variable argument list - you cannot vary the order of the named arguments from their definition

package org.fool.scala.classes

class Family(mom:String, dad:String, kids:String*)

object NamedAndVariableArgs extends App {
  new Family(mom="Mom", dad="Dad")
  // Doesn't work
  // new Family(dad="Dad", mom="Mom")
  new Family(mom="Mom", dad="Dad", kids="Hello", "World")
  // Doesn't work
  // new Family(dad="Mom", mom="Dad", kids="Hello", "World")

}