快学Scala习题解答—第十一章 操作符

11 操作符
11.1 根据优先级规则,3 + 4 -> 5和3 -> 4 + 5是如何被求值的？
在REPL中执行即可得到结果。都是从左至右执行
12.2 BigInt类有一个pow方法,但没有用操作符字符。Scala类库的设计者为什么没有选用**(像Fortran那样)或者^(像Pascal那样)作为乘方操作符呢？
Scala中的操作符就是方法，其优先级是根据首字母来判断的，优先级如下
最高优先级:除以下字符外的操作符字符
 * / % 
+ - 
: 
= ! 
< > 
& 
ˆ 
| 
非操作符
最低优先级:赋值操作符
一般乘方的操作符是优于乘法操作的，如果使用**作为乘方的话，那么其优先级则与*相同，而如果使用^的话，则优先级低于*操作。优先级都是有问题的。故没有使用这两种操作符
11.3 实现Fraction类，支持+*/操作。支持约分，例如将15/-6变为-5/2。除以最大公约数,像这样:
class Fraction(n:Int,d:Int){
    private val num:Int = if(d==0) 1 else n * sign(d)/gcd(n,d);
    private val den:Int = if(d==0) 0 else d * sign(d)/gcd(n,d);
    override def toString = num + "/" + den
    def sign(a:Int) = if(a > 0) 1 else if (a < 0) -1 else 0
    def gcd(a:Int,b:Int):Int = if(b==0) abs(a) else gcd(b,a%b)
    ...
}

import scala.math.absclass Fraction(n: Int, d: Int) {  private val num: Int = if (d == 0) 1 else n * sign(d) / gcd(n, d);  private val den: Int = if (d == 0) 0 else d * sign(d) / gcd(n, d);  override def toString = num + "/" + den  def sign(a: Int) = if (a > 0) 1 else if (a < 0) -1 else 0  def gcd(a: Int, b: Int): Int = if (b == 0) abs(a) else gcd(b, a % b)  def +(other:Fraction):Fraction={    newFrac((this.num * other.den) + (other.num * this.den),this.den * other.den)  }  def -(other:Fraction):Fraction={    newFrac((this.num * other.den) - (other.num * this.den),this.den * other.den)  }  def *(other:Fraction):Fraction={    newFrac(this.num * other.num,this.den * other.den)  }  def /(other:Fraction):Fraction={    newFrac(this.num * other.den,this.den * other.num)  }  private def newFrac(a:Int,b:Int):Fraction={    val x:Int = if (b == 0) 1 else a * sign(b) / gcd(a, b);    val y:Int = if (b == 0) 0 else b * sign(b) / gcd(a, b);    new Fraction(x,y)  }}object Test extends App{  val f = new Fraction(15,-6)  val p = new Fraction(20,60)  println(f)  println(p)  println(f + p)  println(f - p)  println(f * p)  println(f / p)}

11.4 实现一个Money类,加入美元和美分字段。提供+,-操作符以及比较操作符==和<。举例来说，Money(1,75)+Money(0,50)==Money(2,25)应为true。你应该同时提供*和/操作符吗？为什么？

class Money(val dollar:BigInt,val cent:BigInt){  def +(other:Money):Money={    val (a,b) = (this.cent + other.cent) /% 100    new Money(this.dollar + other.dollar + a,b)  }  def -(other:Money):Money={    val (d,c) = (this.toCent() - other.toCent()) /% 100    new Money(d,c)  }  private def toCent()={    this.dollar * 100 + this.cent  }  def ==(other:Money):Boolean = this.dollar == other.dollar && this.cent == other.cent  def <(other:Money):Boolean = this.dollar < other.dollar || (this.dollar == other.dollar && this.cent < other.cent)  override def toString = "dollar = " + dollar + " cent = " + cent}object Money{  def apply(dollar:Int,cent:Int):Money={    new Money(dollar,cent)  }  def main(args:Array[String]){    val m1 = Money(1,200)    val m2 = Money(2,2)    println(m1 + m2)    println(m1 - m2)    println(m1 == m2)    println(m1 < m2)    println(Money(1,75)+Money(0,50))    println(Money(1,75)+Money(0,50)==Money(2,25))  }}

不需要提供*和/操作。对于金额来说没有乘除操作
11.5 提供操作符用于构造HTML表格。例如:Table() | "Java" | "Scala" || "Gosling" | "Odersky" || "JVM" | "JVM,.NET"应产出:<table><tr><td>Java</td></tr><td>Scala</td></tr><tr><td>Gosling…

class Table{  var s:String = ""  def |(str:String):Table={    val t = Table()    t.s = this.s + "<td>" + str + "</td>"    t  }  def ||(str:String):Table={    val t = Table()    t.s = this.s + "</tr><tr><td>" + str + "</td>"    t  }  override def toString():String={    "<table><tr>" + this.s + "</tr></table>"  }}object Table{  def apply():Table={    new Table()  }  def main(args: Array[String]) {    println(Table() | "Java" | "Scala" || "Gosling" | "Odersky" || "JVM" | "JVM,.NET")  }}

11.6 提供一个ASCIIArt类，其对象包含类似这样的图形:
 /\_/\
( ' ' )
(  -  )
 | | |
(__|__)
提供将两个ASCIIArt图形横向或纵向结合的操作符。选用适当优先级的操作符命名。纵向结合的实例
 /\_/\     -----
( ' ' )  / Hello \
(  -  ) <  Scala |
 | | |   \ Coder /
(__|__)    -----

import collection.mutable.ArrayBufferclass ASCIIArt(str:String){  val arr:ArrayBuffer[ArrayBuffer[String]] = new ArrayBuffer[ArrayBuffer[String]]()  if (str != null && !str.trim.eq("")){    str.split("[\r\n]+").foreach{      line =>      val s = new ArrayBuffer[String]()      s += line      arr += s    }  }  def this(){    this("")  }  def +(other:ASCIIArt):ASCIIArt={    val art = new ASCIIArt()    val length = if (this.arr.length >= other.arr.length) this.arr.length else other.arr.length    for(i <- 0 until length){      val s = new ArrayBuffer[String]()      val thisArr:ArrayBuffer[String] = if (i < this.arr.length) this.arr(i) else new ArrayBuffer[String]()      val otherArr:ArrayBuffer[String] = if (i < other.arr.length) other.arr(i) else new ArrayBuffer[String]()      thisArr.foreach(s += _)      otherArr.foreach(s += _)      art.arr += s    }    art  }  def *(other:ASCIIArt):ASCIIArt={    val art = new ASCIIArt()    this.arr.foreach(art.arr += _)    other.arr.foreach(art.arr += _)    art  }  override def toString()={    var ss:String = ""    arr.foreach{      ss += _.mkString(" ") + "\n"    }    ss  }}object Test extends App{  val a = new ASCIIArt(""" /\_/\                         |( ' ' )                         |(  -  )                         | | | |                         |(__|__)                         |""".stripMargin)  val b = new ASCIIArt( """    -----                          |  / Hello \                          | <  Scala |                          |  \ Coder /                          |    -----                          |""".stripMargin)  println(a + b * b)  println((a + b) * b)  println(a * b)}

11.7 实现一个BigSequence类,将64个bit的序列打包在一个Long值中。提供apply和update操作来获取和设置某个具体的bit

class BigSequence{  var num = new Array[Int](64)  for (i <- 0 until num.length){    num(i) = -1  }  def pack():Long={    num.filter(_ >= 0).mkString.toLong  }}object BigSequence{  def apply(num:Int):BigSequence={    val b = new BigSequence    var i = 0    num.toString.foreach{      n=>      b.num(i) = n.getNumericValue      i+=1    }    b  }  def main(args: Array[String]) {    val b = BigSequence(10100)    println(b.pack())  }}

11.8 提供一个Matrix类—你可以选择需要的是一个2*2的矩阵，任意大小的正方形矩阵，或m*n的矩阵。支持+和*操作。*操作应同样适用于单值，例如mat*2。单个元素可以通过mat(row,col)得到

class Matrix(val x:Int,val y:Int){  def +(other:Matrix):Matrix={    Matrix(this.x + other.x,this.y + other.y)  }  def +(other:Int):Matrix={    Matrix(this.x + other,this.y + other)  }  def *(other:Matrix):Matrix={    Matrix(this.x * other.x,this.y * other.y)  }  def *(other:Int):Matrix={    Matrix(this.x * other,this.y * other)  }  override def toString()={    var str = ""    for(i <- 1 to x){      for(j <- 1 to y){        str += "*"      }      str += "\n"    }    str  }}object Matrix{  def apply(x:Int,y:Int):Matrix= new Matrix(x,y)  def main(args: Array[String]) {    val m = Matrix(2,2)    val n = Matrix(3,4)    println(m)    println(n)    println(m + n)    println()    println(m * n)    println()    println(m + 2)    println()    println(n * 2)    println()  }}

11.9 为RichFile类定义unapply操作，提取文件路径，名称和扩展名。举例来说，文件/home/cay/readme.txt的路径为/home/cay,名称为readme,扩展名为txt

class RichFile(val path:String){}object RichFile{  def apply(path:String):RichFile={    new RichFile(path)  }  def unapply(richFile:RichFile) = {    if(richFile.path == null){      None    } else {      val reg = "([/\\w+]+)/(\\w+)\\.(\\w+)".r      val reg(r1,r2,r3) = richFile.path      Some((r1,r2,r3))    }  }  def main(args: Array[String]) {    val richFile = RichFile("/home/cay/readme.txt")    val RichFile(r1,r2,r3) = richFile    println(r1)    println(r2)    println(r3)  }}

11.10 为RichFile类定义一个unapplySeq，提取所有路径段。举例来说，对于/home/cay/readme.txt，你应该产出三个路径段的序列:home,cay和readme.txt

class RichFile(val path:String){}object RichFile{  def apply(path:String):RichFile={    new RichFile(path)  }  def unapplySeq(richFile:RichFile):Option[Seq[String]]={    if(richFile.path == null){      None    } else {      Some(richFile.path.split("/"))    }  }  def main(args: Array[String]) {    val richFile = RichFile("/home/cay/readme.txt")    val RichFile(r @ _*) = richFile    println(r)  }}