Scala in Impatient 习题解答6 对象A1

本章只有8题

1. object Conversions {
       private val i2c = 30.48
       private val g2l = 3.785411784
       private val m2k = 1.609344
   
       def inchesToCentimeters(inch: Double): Double = {
           inch * i2c 
       }
   
       def gallonsToLiters(gallon: Double): Double = {
           gallon * g2l
       }
   
       def milesToKilometers(mile: Double): Double = {
           mile * m2k
       }
   }
   

   scala> Conversions.inchesToCentimeters(1)
   res23: Double = 30.48
   

2. abstract class UnitConversion {
       def converse(from: Double): Double
   }
   object InchesToCentimeters extends UnitConversion {
       private val i2c = 30.48
   
       override def converse(inch: Double): Double = {
           inch * i2c 
       }
   }
   
   object GallonsToLiters extends UnitConversion {
       private val g2l = 3.785411784
   
       override def converse(gallon: Double): Double = {
           gallon * g2l
       }
   }
   
   object MilesToKilometers extends UnitConversion {
       private val m2k = 1.609344
   
       override def converse(mile: Double): Double = {
           mile * m2k
       }
   }
   

3. 这肯定不是一个好主意。Point有move方法，setLocation方法。这些作为Origin(原 点) 来说都不是很合适。

    import java.awt.Point
   
    object Origin extends Point {
    }
   

4. class Point(var x: Int, var y: Int) {}
   object Point {
       def apply(x: Int, y: Int) = {
           new Point(x, y)
       }
   }
   

5. object Reverse extends App {
       for (str <- args.reverse) print(str + " ")
   }
   

6. 这四个花色的符号win下选输入法的特殊符号软键盘。在lin下可以用vim。在vim中输入:dig可以找到分别对应cS,cH,cD,cC。进入vim插入模式按<CTRL-K>，然后分别输入即可（注意大小写）

    object PokerFace extends Enumeration {
        type PokerFace = Value
        val SPADES = Value("♠")
        val HEARTS = Value("♡")
        val DIAMONDS = Value("♢")
        val CLUBS = Value("♣")
    }
   

验证

    scala> PokerFace.SPADES
    res59: PokerFace.Value = ♠

    scala> PokerFace.HEARTS
    res60: PokerFace.Value = ♡

    scala> PokerFace.DIAMONDS
    res61: PokerFace.Value = ♢

    scala> PokerFace.CLUBS
    res62: PokerFace.Value = ♣

1. 直接在6的对象基础上加方法

    object PokerFace extends Enumeration {
        type PokerFace = Value
        val SPADES = Value("♠")
        val HEARTS = Value("♡")
        val DIAMONDS = Value("♢")
        val CLUBS = Value("♣")
   
        def isRed(poker: PokerFace): Boolean = {
            poker.id == HEARTS.id || poker.id == DIAMONDS.id
        }
    }
   

2. RGB如果分别用8位表示，红是0xff0000,绿是0x00ff00,蓝是0x0000ff。以此类推 ，8个顶点分别是(0,0,0)(0,0,1)(0,1,0)(0,1,1)(1,0,0)(1,0,1)(1,1,0)(1,1,1)

RGB的立方体模型参考维基百科http://en.wikipedia.org/wiki/RGB_color_model

```scala
object RGBCube extends Enumeration {
    type RGBCube = Value
    private val base = 0x0000ff
    private val vertexes = new Array[Int](8)
    for (i <- 0 until vertexes.length; j <- 0 to 2) {
        if ((i & 1 << j) != 0) vertexes(i) += base << j * 8
    }

    val V1 = Value(vertexes(0))
    val V2 = Value(vertexes(1))
    val V3 = Value(vertexes(2))
    val V4 = Value(vertexes(3))
    val V5 = Value(vertexes(4))
    val V6 = Value(vertexes(5))
    val V7 = Value(vertexes(6))
    val V8 = Value(vertexes(7))
}
```

验证

    scala> RGBCube.V4.id.toHexString
    res24: String = ffff