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？

1	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：

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

应产出：

1	<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.ArrayBuffer class 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.ArrayBuffer class 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.ArrayBuffer class 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.File object 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)} } }