1. 编写一个Conversions对象，加入inchesToCentimeters、gallonsToLiters和milesToKilometers方法。
object Conversions {
def main(args: Array[String]){
printf("1 inch = %g centimeters\n", inchesToCentimeters(1))
printf("2 gallons = %g liters\n", gallonsToLiters(2))
printf("3 miles = %g centimeters\n", milesToKilometers(3))
}
def inchesToCentimeters(inches:Double)={
inches * 2.54
}
def gallonsToLiters(gallons:Double)={
gallons * 3.7854118
}
def milesToKilometers(miles:Double)={
miles * 1.609344
}
}
/*result
1 inch = 2.54000 centimeters
2 gallons = 7.57082 liters
3 miles = 4.82803 centimeters
*/
2. 前一个练习不是很面向对象。提供一个通用的超类UnitConversions并定义扩展该超类的inchesToCentimeters、gallonsToLiters和milesToKilometers对象。
abstract class UnitConversions{
def convert(amt:Double): Double
}
object inchesToCentimeters extends UnitConversions{
override def convert(amt:Double)= amt * 2.54
}
object gallonsToLiters extends UnitConversions{
override def convert(amt:Double)= amt * 3.7854118
}
object milesToKilometers extends UnitConversions{
override def convert(amt:Double)= amt * 1.609344
}
printf("1 inch = %g centimeters\n", inchesToCentimeters.convert(1))
printf("2 gallons = %g liters\n", gallonsToLiters.convert(2))
printf("3 miles = %g centimeters\n", milesToKilometers.convert(3))
/*result
1 inch = 2.54000 centimeters
2 gallons = 7.57082 liters
3 miles = 4.82803 centimeters
*/
3. 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类中的getLocation方法返回的是Point对象，如果想返回Origin对象，需要Origin类才行。
import java.awt._
object Origin extends Point{
override def getLocation:Point = super.getLocation
}
Origin.move(2,3)
println(Origin.toString)
/*result
Main$$anon$1$Origin$[x=2,y=3]
*/
4. 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。
class Point private(val x:Int, val y:Int){
override def toString = "Point at [x=%d,y=%d]".format(x,y)
}
object Point{
def apply(x:Int, y:Int) = new Point(x,y)
}
val a = Point(3,4)
println(a.toString)
/*result
Point at [x=3,y=4]
*/
5. 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应该打印出World Hello。
object Reverse{
def main(args:Array[String]){
for(i <- (0 until args.length).reverse) print(args(i) + " ")
}
}
/* The following code did not work for me.
object Reverse extends App{
for(i <- (0 until args.length).reverse) print(args(i) + " ")
}
*/
/*result
World Hello
*/
6. 编写一个扑克牌4种花色的枚举，让其toString方法分别返回♠♥♦或♣。
object Poker extends Enumeration with App{
val Heart = Value(3, "♥")
val Diamond = Value(4, "♦")
val Club = Value(5, "♣")
val Spade = Value(6, "♠")
println(Poker.Heart)
println(Poker.Diamond)
println(Poker.Club)
println(Poker.Spade)
}
7. 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 Heart = Value(3, "")
val Diamond = Value(4, "")
val Club = Value(5, "")
val Spade = Value(6, "")
def color(c: Card.Value){
if(c == Card.Club || c == Card.Spade) print("Black")
else print("Red")
}
color(Card.Heart)
}
/*
Red
*/
8. 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 YELLO = Value(0xffff00,"Yellow")
val WHITE = Value(0xffffff,"White")
val BLUE = Value(0x0000ff,"Blue")
val MAGENTA = Value(0xff00ff,"Magenta")
}