Scala练习（十一）

\1. 根据优先级规则， 3 + 4 -> 5 和 3 -> 4 + 5 是如何被求值的？

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在REPL中执行即可得到结果。都是从左至右执行

\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？

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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

\3. 实现Fraction类，支持 + - * / 操作，支持约分, 例如将 15 / -6 变成 -5 / 2。除以最大公约数，像这样：

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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) a.abs else gcd(b, a % b)}

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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) a.abs else gcd(b, a % b)  def +(a: Fraction) : Fraction = {    return new Fraction(this.num * a.den + a.num * this.den, this.den * a.den);  }     def -(a: Fraction) : Fraction = {    return new Fraction(this.num * a.den - a.num * this.den, this.den * a.den);  }     def *(a: Fraction) : Fraction = {    return new Fraction(this.num * a.num , this.den * a.den);  }     def /(a: Fraction) : Fraction = {    return new Fraction(this.num * a.den , this.den * a.num);  } } object FractionTest extends App {  val num1 = new Fraction(3, 4);  val num2 = new Fraction(1, 2);    println(num1);  println(num2);  println(num1 + num2);  println(num1 - num2);  println(num1 * num2);  println(num1 / num2);}

\4. 实现一个Money类，加入美元和美分字段。提供 +、-操作符已经比较操作符==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？

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class Money(private val d: Int, private val c: Int) {  private var dollars = d;  private val cents = {    if (c >= 100) {      dollars += c / 100      c % 100    } else if (c < -100) {      dollars -= c / 100      c % 100    } else {      c    }  }     override def toString = {    "(" + dollars + "," + cents + ")"  }     def +(a: Money) = {    new Money(this.dollars + a.dollars, this.cents + a.cents);  }     def -(a: Money) = {    new Money(this.dollars - a.dollars, this.cents - a.cents);  }     def ==(a: Money) = {    (this.dollars * 100 + this.cents) == (a.dollars * 100 + a.cents)  }     def <(a: Money) = {    (this.dollars * 100 + this.cents) < (a.dollars * 100 + a.cents)  } }object Money {  def apply(d: Int, c: Int) = new Money(d, c);    def unapply(o: Money) = {    Some((o.dollars, o.cents))  } } object MoneyTest extends App {  val c = Money(2, 175);  val Money(a: Int, b: Int) = c  println(a)  println(Money(1, 75) + Money(0, 50) == Money(2, 25))}

对于美元操作乘、除是没有意义.

\5. 提供操作符用于构造HTML表格。例如：

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Table() | "Java" | "Scala" || "Gosling" | "Odersky" || "JVM" | "JVM, .NET"

应产出：

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<table><tr><td>Java</td><td>Scala</td></tr><tr><td>Gosling</td><td>Odersky</td></tr><tr><td>JVM</td><td>JVM, .NET</td></tr></table>

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import scala.collection.mutable.ArrayBufferclass Table{  private val trTags : ArrayBuffer[String] = ArrayBuffer();  private val tdTags : ArrayBuffer[String] = ArrayBuffer();  def |(str: String) = {    tdTags += str    this  }  def ||(str: String) : Table= {    trTags += "<tr><td>" + tdTags.mkString("</td><td>") + "</td><tr>"    tdTags.clear()         tdTags += str    this  }  override def toString = {    if (!tdTags.isEmpty) {      trTags += "<tr><td>" + tdTags.mkString("</td><td>") + "</td><tr>"    }         "<table>" + trTags.mkString("")+ "</table>"  } } object Table {  def apply() = new Table()} object TableTest extends App {  val str = Table() | "Java" | "Scala" || "Gosling" | "Odersky" || "JVM" | "JVM, .NET"  println(str)}

\6. 提供一个ASCIIArt 类，其对象包含类似这样的图形：

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 /\_/\( ' ' )(  _  ) | | |(__|__)

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。横向结合的实例：

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 /\_/\    -----( ' ' ) / Hello \(  _  )<  Scala | | | |  \ Coder /(__|__)   -----

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import scala.collection.mutable.ArrayBufferclass ASCIIArt(str: String) {  val artMap : ArrayBuffer[String] = new ArrayBuffer[String]()  if (str != null && !str.trim.eq("")) {    str.split("[\r\n]+").foreach((line: String) => {      val tmp = new ArrayBuffer[String]();      artMap += line    })  }  def this() {    this("")  }  def +(other: ASCIIArt) : ASCIIArt = {    val art = new ASCIIArt()    val length = if (this.artMap.length >= other.artMap.length) this.artMap.length else other.artMap.length    for (i <- 0 until length) {      val thisCur : String = if (this.artMap.isDefinedAt(i)) this.artMap(i) else ""       val otherCur : String = if (this.artMap.isDefinedAt(i)) other.artMap(i) else ""        art.artMap += thisCur + otherCur    }     art  }  def *(other: ASCIIArt) : ASCIIArt = {    val art = new ASCIIArt()    art.artMap ++= this.artMap    art.artMap ++= other.artMap    art  }             override def toString = {    artMap.mkString("\n")   }    } object ASCIIArt {  def apply(str: String) = new ASCIIArt(str)} object ASCIIArtTest extends App {  val a1 = ASCIIArt(""" /\_/\                      |( ' ' )                      |(  -  )                      | | | |                       |(__|__)                      |""".stripMargin)  val a2 = ASCIIArt("""    -----                      |  / Hello \                      | <  Scala |                      |  \ Coder /                      |    -----                      |""".stripMargin)  println(a1 + a2)  println(a1 * a2)}

\7. 实现一个BigSequence 类，将64个bit的序列包在一个Long值中。提供apply和update操作来获取和设置某个位置具体的bit

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// todo

\8. 提供一个Matrix类—-你可以选择需要的是一个2x2的矩阵，任意大小的正方形矩阵，或是mxn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

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import scala.collection.mutable.ArrayBufferclass Matrix(private val data: Array[Int], private val nrow: Int){  private val matrixData : Array[Array[Int]] = {    val cols = (data.length.toFloat / nrow).ceil.toInt    val result : Array[Array[Int]] = Array.ofDim[Int](nrow, cols);    for (i <- 0 until nrow) {      for (j <- 0 until cols) {        val index = i*cols + j        result(i)(j) = if (data.isDefinedAt(index)) data(index) else 0      }    }    result  }  override def toString = {    var str = ""    matrixData.map((p: Array[Int]) => {      p.mkString(",")    }).mkString("\n")  }  def *(a: Matrix) = {    val data: ArrayBuffer[Int] = ArrayBuffer();    for (i <- 0 to  a.matrixData.length - 1) {      for (j <- 0 to a.matrixData(0).length - 1) {        data += a.matrixData(i)(j) * this.matrixData(i)(j)      }    }    new Matrix(data.toArray, a.matrixData.length)  }  def *(a: Int) = {    val data: ArrayBuffer[Int] = ArrayBuffer();    for (i <- 0 to  this.matrixData.length - 1) {      for (j <- 0 to this.matrixData(0).length - 1) {        data += this.matrixData(i)(j) * a       }    }    new Matrix(data.toArray, this.matrixData.length)  }  def +(a: Matrix) = {    val data: ArrayBuffer[Int] = ArrayBuffer();    for (i <- 0 to  this.matrixData.length - 1) {      for (j <- 0 to this.matrixData(0).length - 1) {        data += this.matrixData(i)(j) + a.matrixData(i)(j)      }    }    new Matrix(data.toArray, this.matrixData.length)  }  def mat(row: Int, col: Int) = {    matrixData(row - 1)(col - 1)  }}object MatrixTest extends App {  val m = new Matrix(Array(1,2,3,4), 3)  val n = new Matrix(Array(1,2,3,4), 3)  println(m * n)  println(m + n)  println(m.mat(2, 2))  println(n * 10)}

\9. 为RichFile 类定义unapply操作，提取文件路劲、名称和扩展名。举例来说，文件/home/cay/readme.txt的路劲为/home/cay, 名称为 readme, 扩展名txt

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import java.io.Fileobject RichFile {   def unapply(filePath : String) = {    val file = new File(filePath)    val ext = file.getName.split("\\.")    Some((file.getParent, file.getName, ext(1)))  }                                    }                                      object RichFileTest extends App {  val RichFile(path, fileName, ext) = "/home/cay/readme.txt"  println(path)  println(fileName)  println(ext)}

\10. 为RichFile 类定义一个unapplySeq, 提取所有路阶段。举例来说，对于/home/cay/readme.txt,你应该产出三个路劲的序列: home，cay,readme.txt

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object RichFile {  def unapplySeq(filePath : String) : Option[Seq[String]]= {    Some(filePath.trim.split("\\/"))  } } object RichFileTest extends App {  val str = "/home/cay/readme.txt"  str match {    case RichFile(str0, str1, str2, str3) => {      println(str1);      println(str2);    }     case _ => {println(str)}  } }