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快学Scala习题解答—第六章 对象

对象

编写一个Conversions对象，加入inchesToCentimeters,gallonsToLiters和milesToKilometers方法

object Conversions{
    def inchesToCentimeters(){}
    def gallonsToLiters(){}
    def milesToKilometers(){}
}

前一个练习不是很面向对象。提供一个通用的超类UnitConversion并定义扩展该超类的InchesToCentimeters,GallonsToLiters和MilesToKilometers对象

abstract class UnitConversion{
  def inchesToCentimeters(){}
  def gallonsToLiters(){}
  def milesToKilometers(){}
}
object InchesToCentimeters extends UnitConversion{
  override def inchesToCentimeters() {}
}
object GallonsToLiters extends UnitConversion{
  override def gallonsToLiters() {}
}
object MilesToKilometers extends UnitConversion{
  override def milesToKilometers() {}
}

定义一个扩展自java.awt.Point的Origin对象。为什么说这实际上不是个好主意？(仔细看Point类的方法)

Point中的getLocation方法返回的是Point对象，如果想返回Origin对象，需要Origin类才行

object Origin extends Point with App{
  override def getLocation: Point = super.getLocation
  Origin.move(2,3)
  println(Origin.toString)
}

定义一个Point类和一个伴生对象,使得我们可以不用new而直接用Point(3,4)来构造Point实例

apply方法的使用

class Point(x:Int,y:Int){
  override def toString: String = "x = " + x + " y = " + y
}
object Point extends App{
  def apply(x:Int,y:Int)={
    new Point(x,y)
  }
  val p = Point(1,2)
  println(p)
}

编写一个Scala应用程序,使用App特质,以反序打印命令行参数,用空格隔开。举例来说,scala Reverse Hello World应该打印World Hello

object Reverse extends App{
  args.reverse.foreach(arg => print(arg  + " "))
}

编写一个扑克牌4种花色的枚举,让其toString方法分别返回♣,@<span style="color:red">♦@</span>,@<span style="color:red">♥@</span>,♠

object Card extends Enumeration with App{
  val M = Value("♣")
  val T = Value("♠")
  val H = Value("♥")
  val F = Value("♦")
  println(Card.M)
  println(Card.T)
  println(Card.H)
  println(Card.F)
}

实现一个函数,检查某张牌的花色是否为红色

object Card extends Enumeration with App{
  val M = Value("♣")
  val T = Value("♠")
  val H = Value("♥")
  val F = Value("♦")
  def color(c:Card.Value){
    if(c == Card.M || c == Card.T) print("Black")
    else print("Red")
  }
  color(Card.H)
}

编写一个枚举,描述RGB立方体的8个角。ID使用颜色值(例如:红色是0xff0000)

object RGB extends Enumeration with App{
  val RED = Value(0xff0000,"Red")
  val BLACK = Value(0x000000,"Black")
  val GREEN = Value(0x00ff00,"Green")
  val CYAN = Value(0x00ffff,"Cyan")
  val YELLOW = Value(0xffff00,"Yellow")
  val WHITE = Value(0xffffff,"White")
  val BLUE = Value(0x0000ff,"Blue")
  val MAGENTA = Value(0xff00ff,"Magenta")
}