Scala代码练习

1、编程实现百分制转换成五级制，规则如下：
90~100分，返回优秀；
80~89分，返回良好；
70~79分，返回中等；
60~69分，返回及格；
60分以下，返回不及格。

object grade {
  def main(args: Array[String]): Unit = {
    val num = 70
    if(num>=90){
      println("优秀")
    }else if(num>=80){
      println("良好")
    }
    else if (num>=70) {
      println("中等")
    }
    else if (num>=60) {
      println("及格")
    }
    else if (num<60) {
      println("不及格")
    }
  }
}

2、使用while或do…while语句打印1~50，要求每行包含5个数，如下：

object whileTest {
  def main(args: Array[String]): Unit = {
    var num=1
    while(num<=50){
      print(num+" ")
      if(num%5==0){
        println()
      }
      num+=1
    }
  }
}

3、使用for语句打印九九乘法表，运行结果如下：

object jiujiu {
  def main(args: Array[String]): Unit = {
    var i=1
    while(i<=9){
      var j=1
      while(j<=i){
        var ans=i*j
        print(i+"*"+j+"="+ans+" ")
        j+=1
      }
      i+=1
      println()
    }
  }
}

4、定义Rational类，参数分别是要操作的三个有理数，要求：
(1)参数是Int；
(2)定义一个方法对参数求和；
(3)实现对指定的一个参数加10和20；

class Rational(val x:Int=10,var y:Int,z:Int=20){
  def sum():Int={
    x+y+z
  }
}
object Rational {
  def main(args: Array[String]): Unit = {
    val r=new Rational(1,2,3)
    println(s"sum1=${r.sum()}")
    val r1=new Rational(y=1)
    println(s"sum2=${r1.sum()}")
    val r2=new Rational(5,y=1,10)
    println(s"sum3=${r2.sum()}")
  }
}

5、定义一个Car类，提供四组构造器，要求：
(1)只读属性：制造商、型号和年份；
(2)可读写属性：车牌号；
(3)每一组构造器制造商和型号必填；
(4)年份和车牌号可选，如果未设置年份为-1，车牌为空字符串。

object Car {
  def main(arg: Array[String]) {
    var car1 = new Car("BWM", "A6")
    car1.PrintAll()
    var car2 = new Car("BWM", "A6", 2000)
    car2.PrintAll()
    var car3 = new Car("BWM", "A6", "A01")
    car3.PrintAll()
    var car4 = new Car("BWM", "A6", 2000, "A01")
    car4.PrintAll()
  }
  class Car(val producerName: String, val productName: String, val productyear: Int, var num: String) {
    def this(producerName: String, productName: String) {
      this(producerName, productName, -1, "")
    }
    def this(producerName: String, productName: String, productyear: Int) {
      this(producerName, productName, productyear, "")
    }
    def this(producerName: String, productName: String, num: String) {
      this(producerName: String, productName: String, -1, num)
    }
    def PrintAll() {
      println("producerName:" + producerName + " productName:" + productName + " productyear:" + productyear + " num:" + num)
    }
  }
}

6、创建一个Student类和它的伴生对象，为Student类和它的伴生对象分别创建私有属性secret，并相互访问。

object Student {
  private val secrect1 = "i am secrect1 ******"

  def accessCompanionClass(s: Student) = {
    println(s"access Companion Class private field = ${s.secrect2}")
  }
}

class Student {
  private val secrect2 = "i am secrect2 *****"

  def accessCompanionObject() = {
    println(s"access Companion Object private field = ${Student.secrect1}")
  }
}

object Runl {
  def main(args: Array[String]): Unit = {
    Student.accessCompanionClass(new Student())
    new Student().accessCompanionObject()
  }
}

7、定义一个Point类和它的伴生对象，要求不使用new，而是用Point(3,4)创建对象，并求横纵坐标之和。

class Point{
 var x=1
 var y=1
 def sum={
   x+y
 }
}
object Point{
//当对象（伴生对象）以函数的方式进行调用时，scala 会隐式地将调用改为在该对象上调用apply方法。
 def apply(x:Int,y:Int):Point = {
   var p = new Point()
   p.x=x
   p.y=y
   p
 }
}
object test{
 def main(args: Array[String]): Unit = {
   val p1=Point(3,4)
   val sum1=p1.sum
   print(sum1)
 }
}

8、定义一个Teacher类，包括名字、性别、年龄和职工号属性，覆写equals方法，满足：
(1)若职工号相等，则认为两个对象相等。
(2)所有属性相等，则认为两个对象相等。

class teacher(val name:String,val male:String,val age:String,val num:String){
 def equals(obj:teacher):Boolean = {
  if(obj.num==this.num){
  true
  }else{
    false
  }
 }
}
object teacher{
 def main(args: Array[String]): Unit = {
   var a = new teacher("name1", "male1", "age1", "num1")
   var b = new teacher("name2", "male2", "age2", "num1")
   println(a.equals(b))
 }
}

class teacher(val name:String,val male:String,val age:String,val num:String){
 def equals(obj: teacher): Boolean = {
   if (obj.name == this.name&&obj.male == this.male&&obj.age == this.age&&obj.num == this.num) {
     true
   } else {
     false
   }
 }
}
object teacher{
 def main(args: Array[String]): Unit = {
   var a = new teacher("name1", "male1", "age1", "num1")
   var b = new teacher("name2", "male2", "age2", "num1")
   println(a.equals(b))
 }
}

9、定义一个方法，对两个整数相除，如果除数是0，则抛出 “can not divide by zero”异常。

object zero {
 def chuFa(a: Int, b: Int): Unit = {
   if (b == 0) {
     println("can not divide by zero")
   }
   else {
     println(a / b)
   }
 }
 def main(args: Array[String]): Unit = {
   chuFa(3, 0)
 }
}

10、定义一个exeAdd函数，接受一个带有整型参数的函数，对整数加10。定义一个exeAndPrint方法，接受一个带两个参数的函数和两个整型，将整型参数赋予函数，计算打印结果。

object RunWithParFuntion {
 def main(args: Array[String]): Unit = {
   val sayhello = () => {
     print("hello scala function")
   }
   exeFuctionWithOutPar(sayhello)
   val plusTen = (i: Int) => {
     i + 10
   }
   exeAdd(plusTen)
   val sum = (x: Int, y: Int) => x + y
   val multi = (x: Int, y: Int) => x * y
   exeAndPrint(sum, 2, 3)
   exeAndPrint(multi, 2, 3)
 }
 def exeFuctionWithOutPar(callback: () => Unit): Unit = {
   callback()
 }
 def exeAdd(callback: Int => Int): Int = {
   callback(8)
 }
 def exeAndPrint(callback: (Int, Int) => Int, x: Int, y: Int): Unit = {
   val result = callback(x, y)
   println(s"callback=$result")
 }
}

11、定义一个函数为wrapHTML，添加前后缀（如<div>和</div>），传递部分参数，打印结果。

class RunPartialFunction {
 def warpHTML(pref: String, context: String, suffix: String): String = {
   pref + context + suffix
 }
 def mutlti(x: Int, y: Int, z: Int) = x * y * z
}
object RunPartialFunction {
 def main(args: Array[String]): Unit = {
   val p = new RunPartialFunction()
   val htmlwithp = p.warpHTML("<p>", _: String, "<p>")
   println("p=" + htmlwithp("i am p"))
   val htmlwithdiv = p.warpHTML("<div>", _: String, "<div>")
   println("div=" + htmlwithdiv("i am div"))
   val f1 = p.mutlti(_: Int, 2, _: Int)
   println(f1(4, 5))
   val f2 = p.mutlti(_: Int, 2, 3)
   println(f2(5))
   val f3 = p.mutlti(_: Int, _: Int, _: Int)
   println(f3(5, 1, 2))
 }
}

12、应用高阶函数，打印三角形；字符串数组，将其转成大写，再过滤掉以S开头的字符串。实现数字字符串的求和，如 Array("1,2", "3,4") 结果为10。

object RunHighFun {
 def main(args: Array[String]): Unit = {
   val array = Array(1, 2, 3, 4, 5)
   val s = array.map(x => "*" * x)
   array.map("*" * _).foreach(println(_))
   val s2 = Array("scala", "java", "spark")
   s2.map(x => x.toUpperCase).filter(s => (!s.startsWith("S"))).foreach(println(_))
   val sumarrary = Array("1,2", "3,4")
   val sum = sumarrary.flatMap(x => x.split(",")).map(_.toInt).reduce(_ + _)
   println(s"sum=$sum")
 }
}

13、编写函数values(fun:(Int)=>Int, low:Int, high:Int)，该函数输出一个集合，对应给定区间内给定函数的输入和输出。例如，values(x=>x*x,-5,5)应该产生一个对偶的集合(-5,25),(-4,16),(-3,9),…,(5,25)。

object LowHigh {
 def main(args: Array[String]): Unit = {
   val f = (x: Int) => x * x
   val result = values(f, -5, 5)
   result.foreach(println(_))
 }
 def values(fun: (Int) => Int, low: Int, high: Int): IndexedSeq[(Int, Int)] = {
   for (i <- low to high) yield (i, fun(i))
 }
}

14、编写函数largest(fun:(Int)=>Int, inputs:Seq[Int])，输出在给定输入序列中给定函数的最大值。例如，largest(x=>10x-xx,1 to 10)应该返回25。要求不得使用循环或递归。

object findMaXdef {
 def main(args: Array[String]): Unit = {
   val f = (x: Int) => 10 * x - x * x
   val maxValue = largestValue(f, 1 to 10)
   println(s"maxValue=$maxValue")
   val maxIndex = largestIndex(f, 1 to 10)
   println(s"maxIndex=$maxIndex")
 }
 def largestValue(fun: (Int) => Int, inputs: Seq[Int]): Int = {
   val result = inputs.map(x => fun(x))
   result.reduce((x, y) =>
     if (x > y)
       x
     else
       y
   )
 }
 def largestIndex(fun: (Int) => Int, inputs: Seq[Int]): Int = {
   inputs.reduce((x, y) =>
     if (fun(x) > fun(y))
       x
     else
       y
   )
 }
}

15、创建内部类、内部对象以及匿名类，测试使用示例。

object RunNi {
 def main(args: Array[String]): Unit = {
   val p1 = new P("jason", 10) {
     override def print(): Unit = {
       println(s"P($name,$age)")
     }
   }
   p1.print
   println("------------------------------------------")
   val s = new StudentIntenal("scala", 5)
   val grade = new s.Grade("1 grade")
   println(s"grade=${grade.name}")
   s.Uilts1.print("vtil1")
   StudentIntenal.Uilts2.print("util2")
   val pr = new StudentIntenal.printer
   pr.print("printer")
 }
}
abstract class P(var name: String, var age: Int) {
 def print
}
class StudentIntenal(var name: String, var age: Int) {
 class Grade(var name: String)
 object Uilts1 {
   def print(name: String) = {
     println(name)
   }
 }
}
object StudentIntenal {
 class printer {
   def print(name: String) = {
     println(name)
   }
 }
 object Uilts2 {
   def print(name: String) = {
     println(name)
   }
 }
}

16、定义一个Logger测试构造器执行顺序造成空指针问题，两种解决方式。

import java.io.PrintWriter
object RunFile {
 def main(args: Array[String]): Unit = {
   val p = new {
     override val filename = "p052.log"
   }
     with Person051
   p.log("Person052 create log")
 }
}
trait Logger {
 def log(msg: String)
}
trait FileLogger extends Logger {
 val filename: String
 val fileout = new PrintWriter(filename)
 def log(msg: String) = {
   fileout.println(msg)
   fileout.flush()
 }
}
class Person051 extends FileLogger {
 override val filename = "p051.log"
}

17、设计一个Point类，其x和y坐标可以通过构造器提供，提供一个子类LabelPoint，其构造器接受一个标签值和x、y坐标，比如：

object Lpoint {
  def main(args: Array[String]): Unit = {
    val lp = new LabelPoint("black", 1929, 230.07)
    println(s"lp.label=${lp.label},lp.x=${lp.x},lp.y=${lp.y}")
  }
}

class Point(val x: Double, val y: Double) {
  println(s"parent=>x=$x,y=$y")
}

class LabelPoint(val label: String, x: Double, y: Double) extends Point(x, y) {
  println(s"child=>label=$label,=>x=$x,y=$y")
}

18、提供一个cryptoLogger类，将日志消息以凯撒密码加密，默认密钥为3，不过使用者也可重新传值，提供默认密钥和-3作为密钥时的使用示例。

trait Logger {
 def log(str: String, key: Int)
}
class cryptoLogger extends Logger {
 override def log(str: String, key: Int=3): Unit = {
   println(for(i<-str)yield (97+(i-97+key+(if(key<0) 26 else 0))%26).toChar)
 }
}
object RunCrypto {
 def main(args: Array[String]): Unit = {
   new cryptoLogger().log("abc")
   new cryptoLogger().log("abc",-3)
   new cryptoLogger().log("xyz")
   new cryptoLogger().log("xyz",-3)
 }
}

19、定义一个抽象类Item，加入方法price和description，SimpleItem是一个在构造器中给出价格和描述的物件。Bundle是一个可以包含其他物件的物件，其价格是打包中所有物件的价格之和，同时提供一个将物件添加到打包中的机制，以及一个合适的description方法。

class SimpleItem(var p: Double, var desc: String) extends Item {
 def price: Double = p
 def description: String = desc
}
class Bundle(var items: Array[SimpleItem]) extends Item {
 def price: Double = {
   var p = 0.0
   items.foreach(p += _.price)
   p
 }
 def description: String = {
   var desc = ""
   items.foreach(desc += _.description)
   desc
 }
}
object RunItem {
 def main(args: Array[String]): Unit = {
   val s1 = new SimpleItem(12.5, "apple")
   val s2 = new SimpleItem(24.8, "banana")
   val s3 = new SimpleItem(9.9, "orange")
   val fruits = new Bundle(Array(s1, s2, s3))
   println(s"price=${fruits.price},description=${fruits.description}")
 }
}
abstract class Item {
 def price: Double
 def description: String
}

20、测试迭代器的常用方法，有it.next()、it.hasNext、it.duplicate、it.slice(m,n)、it.zip()、it.zipAll()等。

object RunIterator {
 def main(args: Array[String]): Unit = { //1.Range
   val it1 = Iterator(1 to 5)
   println(it1.hasNext, it1.next())
   val it2 = Iterator(1, 2, 3)
   println(it2.hasNext, it2.next())
   println(it2.hasNext, it2.next())
   println(it2.hasNext, it2.next()) //Iterator(1,2,3,4,5,6,7,8,9,10)
   val it3 = Iterator(1 to 5: _*)
   while (it3.hasNext) {
     println(it3.next())
   }
   val it4 = Iterator(1 to 3: _*)
   it4.foreach(x => println(x))
   it4.foreach(x => println(x))
   val it5 = Iterator(6 to 8: _*)
   val (it51, it52) = it5.duplicate
   it5.foreach(x => println(x))
   it52.foreach(x => println(x))
   it5.foreach(x => println(x))
   val it6 = Iterator(9 to 12: _*)
   val it61 = it6.take(2)
   it61.foreach(x => println("it61=" + x))
   it6.foreach(x => println("it6=" + x))
   val it7 = Iterator(13 to 18: _*)
   val it71 = it7.slice(1, 10)
   it71.foreach(x => println("it71=" + x))
   val it8key1 = Iterator("kl", "k2")
   val it8v1 = Iterator("v1", "v2")
   val it8v2 = Iterator("v1")
   val it8k2 = Iterator("k1")
   //      val k1_v1=it8key1.zip(it8v1)
   //      k1_v1.foreach(x => println(x))
   //      val k1_v2 = it8key1.zip(it8v2)
   //      k1_v2.foreach(x => println(x))
   //      val k1_v2 = it8key1.zipAll(it8v2, "default1", "default2")
   //      11 k1_v2.foreach(x => println(x))
   val k2_v1 = it8k2.zipAll(it8v1, "default1", "default2")
   k2_v1.foreach(x => println(x))
 }
}

21、使用不同方式定义可变和不可变数组及多维数组，测试添加元素、删除元素、清空等常用操作。

import scala.collection.mutable.ArrayBuffer
object RunArray {
 def main(args: Array[String]): Unit = {
   val arr1 = new Array[Int](3)
   val arr2 = Array(1, 2d, 31)
   arr2.foreach(println(_))
   val arr3 = Array[Number](1, 2d, 31)
   arr3.foreach(println(_))
   arr1(0) = 7
   arr2(1) = 8
   arr3(2) = 9
   arr1.foreach(x => println(x + ","))
   val r1 = Array.range(1, 5)
   val r3 = Array.fill(2)("scala")
   val r4 = List("a", "b").toArray
   val r5 = Array.tabulate(3)(n => n * n)
   r1.foreach(x => println("r1=" + x + ","))
   println()
   r3.foreach(x => println("r3=" + x + ","))
   println()
   r4.foreach(x => println("r4=" + x + ","))
   println()
   r5.foreach(x => println("r5=" + x + ","))
   println()
 }
 val ab1 = ArrayBuffer(1, 2, 3)
 val ab2 = new ArrayBuffer[String](1)
 ab2 += "a"
 ab2 += "b"
 ab2 ++= Seq("s1", "s2")
 ab2.append("apend1")
 println(s"before=$ab2")
 ab2 -= "b"
 ab2 --= Seq("s1", "s2")
 ab2.remove(0)
 ab2.append("apend4", "apend3", "apend2")
 ab2.remove(1, 3)
 ab2.clear
 println(s"after=$ab2")
 val arr7 = Array[String]("banana", "apple")
 val arr8 = arr7.filter(x => x.startsWith("b"))
 arr8.foreach(x => print("arr7=" + x + ","))
 val marr1 = Array.ofDim[String](2, 2)
 marr1(0)(0) = "a"
 marr1(0)(1) = "b"
 marr1(1)(0) = "c"
 marr1(1)(1) = "d"
 for {
   i <- 0 until 2
   j <- 0 until 2
 } {
   println(s"($i,$j)=${marr1(i)(j)}")
   var marr2 = Array(Array(1, 2), Array(3, 4))
   println(marr2(1)(0))
   marr2 ++= Array(Array(5, 6))
   println(marr2(2)(1))
 }
}

22、通过Nil和::方式构建List列表，测试合并操作、懒加载、zipped操作、折叠操作等。

import scala.collection.mutable.ListBuffer
object RunList {
 def main(args: Array[String]): Unit = {
   //lsit(1,2,3)
   var l1 = 1 :: 2 :: 3 :: Nil
   println(s"l1,head=${l1.head},list(2)=${l1(2)}")
   val l2 = List(4, 5, 6)
   val l3 = l2 :: l1
   println(l3)
   //++,concat
   val l4 = l2 :: l1
   println(l4)
   val lb1 = ListBuffer(7, 8, 9)
   lb1(0) = 99
   println(lb1)
   val s = 1 #:: 2 #:: 3 #:: Stream.empty
   val s2 = s.map(x => x + 1)
   println(s2, s2(2))
   println(s.force)
   val zip1 = (List(1, 2), List(3, 4, 5)).zipped.map(_ * _)
   println(s"zip1=$zip1")
   val words = List("scala", "is", "good")
   val s3 = (" " /: words)(_ + " " + _)
   println(s3)
   val s4 = (words.head /: words.tail)(_ + " " + _)
   println(s4)
 }
}

23、测试Set集合的常用操作，有条件操作、加法、减法、二元逻辑操作、更新等，对于自定义类实现比较方法并排序。

import scala.collection.{SortedSet, mutable}
object RunSet {
 def main(args: Array[String]): Unit = {
   val s1 = Set(1, 2, 3, 3, 2, 5)
   val s2 = Set(3, 5)
   val s3 = Set(4, 5)
   println(s1)
   println(s1.contains(1), s1.contains(6))
   println(s1(2), s1(8))
   println(s"s1 sub s2 ${s1.subsetOf(s2)}")
   println(s"s1 sub s3 ${s1.subsetOf(s3)}")
   println(s"s2 sub s1 ${s1.subsetOf(s1)}")
   println(s"s3 sub s1 ${s1.subsetOf(s1)}")
   var imms = Set(4, 5, 6)
   val imm1 = imms + 3
   val imm2 = imm1 + (22, 33)
   val imm3 = imm2 ++ List(44, 55)
   println(imm3)
   println(imms)
   var ms = scala.collection.mutable.Set(7, 8, 9)
   ms += 10
   ms += (11, 12, 12)
   ms ++= Set(13, 14)
   println(ms)
   ms.retain(_ > 9)
   ms.remove(12)
   ms.clear
   println(ms)
   val ss1 = mutable.SortedSet(10, 3, 11, 2)
   val ss3 = SortedSet(7, 3, 11)
   println(ss1)
   println(ss3)
   val ss2 = mutable.SortedSet("banana", "apple")
   println(ss2)
   val lhs = mutable.LinkedHashSet(1, 8, 4)
   println(lhs)
   val p1 = new Person0701("scala", 12)
   val p2 = new Person0701("java", 2)
   val p3 = new Person0701("c", 20)
   val p = mutable.SortedSet(p1, p2, p3)
   println(p)
 }
}
class Person0701(var name: String, var age: Int) extends Ordered[Person0701] {
 override def compare(that: Person0701): Int = {
   if (this.age == that.age) {
     0
   }
   else if (this.age < that.age) 1
   else -1
 }
}

24、测试Map键值对的相关操作，有查找映射的最大键或值，按键或值排序，按键或值过滤。

import scala.collection.mutable
object RunMap {
 def main(aegs: Array[String]): Unit = {
   val mp = mutable.Map(1 -> "a", 2 -> "b", 3 -> "c")
   mp.retain((k, v) => k > 2)
   println(s"mp=$mp")
   val m = mutable.Map(4 -> "d", 5 -> "e", 6 -> "f")
   val m1 = m.filterKeys(_ > 4)
   println(s"m1=$m1")
   val m2 = m.filterKeys(Set(4, 6))
   println(s"m2=$m2")
   val m3 = m.filter(x => x._1 > 5)
   println(s"m3=$m3")
   val mm = mutable.Map("ab" -> 12, "e" -> 4, "byyy" -> 99, "muuuuuu" -> 17)
   val mm1 = mm.max
   val min1 = mm.min
   println(s"max1=$mm1,min1=$min1")
   val minv = mm.valuesIterator.min
   val maxv = mm.valuesIterator.max
   println(s"minv=$minv,maxv=$maxv")
   val mink = mm.keysIterator.min
   val maxk = mm.keysIterator.max
   println(s"mink=$mink,maxk=$maxk")
   val result = mm.keysIterator.reduceLeft((x, y) => if (x.length > y.length) x else y)
   println(s"result=${result}")
   val sq1 = mm.toSeq.sortBy(_._1)
   val sq2 = mm.toSeq.sortBy(_._2)
   println(s"sq1=$sq1")
   println(s"sq2=$sq2")
   println(sq1.toMap)
   println(sq2.toMap)
   val sq3 = mm.toSeq.sortWith(_._2 > _._2)
   println(s"sq3=$sq3")
   println(sq3.toMap)
 }
}

25、编写一个函数，接受一个字符串的集合，以及一个从字符串到整数值的映射。返回整型的集合，其值为能和集合中某个字符串相对应的映射的值。举例来说，给定Array ("Tom","Fred","Harry")和Map ("Tom"-> 3,"Dick"-> 4,"Harry"-> 5),返回Array(3,5)。提示：用flatMap将get返回的Option值组合在一起。

object Run07 {
 def main(args: Array[String]): Unit = {
   val arr = Array("tom", "fred", "harry")
   val mp = Map("tom" -> 3, "dick" -> 4, "harry" -> 5)
   println(fun2(arr, mp))
 }
 def fun2(input1: Seq[String], input2: Map[String, Int]): Seq[Int] = {
   input1.map(key => input2.getOrElse(key, 0)).filter(value => value != 0)
 }
}

26、测试Scala的模式匹配，模式数据类型有常量、变量、元组、序列、类型、构造器、变量绑定。

object moShiPiPei {
 def main(args: Array[String]): Unit = {
   // 示例代码开始
   // 匹配常量
   val x = 2
   val result1 = x match {
     case 1 => "one"
     case 2 => "two"
     case 3 => "three"
     case _ => "other"
   }
   println(result1) // 输出: two

   // 匹配变量
   val x2 = 5
   val result2 = x2 match {
     case 1 => "one"
     case n => s"other: $n"
   }
   println(result2) // 输出: other: 5

   // 匹配元组
   val tuple = (1, 2)
   val result3 = tuple match {
     case (1, 2) => "one and two"
     case (1, _) => "one and something else"
     case _ => "other"
   }
   println(result3) // 输出: one and two

   // 匹配序列
   val list = List(1, 2, 3)
   val result4 = list match {
     case List(1, 2, 3) => "one, two and three"
     case List(1, _*) => "one and something else"
     case _ => "other"
   }
   println(result4) // 输出: one, two and three

   // 匹配类型
   val value: Any = "hello"
   val result5 = value match {
     case i: Int => s"Int: $i"
     case s: String => s"String: $s"
     case _ => "other"
   }
   println(result5) // 输出: String: hello

   // 匹配构造器
   class Person(val name: String, val age: Int)
   val person = new Person("Alice", 18)
   val result6 = person match {
     case p: Person => s"Person: ${p.name}, ${p.age}"
     case _ => "other"
   }
   println(result6) // 输出: Person: Alice, 18

   // 变量绑定
   val tuple2 = (1, 2)
   val result7 = tuple2 match {
     case (1, x) => s"one and $x"
     case _ => "other"
   }
   println(result7)
 }
}

27、在Scala中，利用List列表实现归并排序。

object MergeSort {
 def merge(l1: List[Int], l2: List[Int]): List[Int] = (l1, l2) match {
   case (Nil, _) => l2
   case (_, Nil) => l1
   case (h1 :: t1, h2 :: t2) =>
     if (h1 < h2) h1 :: merge(t1, l2)
     else h2 :: merge(l1, t2)
 }


 def mergesort(list: List[Int]): List[Int] = list match {
   case Nil => list
   case h :: Nil => list
   case _ =>
     val (l1, l2) = list.splitAt(list.length / 2)
     merge(mergesort(l1), mergesort(l2))
 }

 def main(args: Array[String]): Unit = {
   val num = List(1, 4, 8, 2, 10)
   println(mergesort(num))
 }
}

28、使用列表制作只在叶子节点存放值的树，举例来说，列表((3 8) 2 (5))描述的是如下这样一棵树，编写一个函数计算所有叶子节点中的元素之和。
+
/ | \

2 +
/ \ |
3 8 5

object leafSumTest {
 def main(args: Array[String]): Unit = {
   println(leafsum(List(List(3, 8), 2, 5)))
   def leafsum(tree: List[Any]): Int = {
     var sum = 0
     for (i <- tree) {
       i match {
         case n: Int => sum += n
         case lst: List[Any] => sum += leafsum(lst)
       }
     }
     sum
   }
 }
}

29、创建RunFunction.scala文件，进行隐式参数和隐式值的演练。

object ImplicitParameterExample {
 // 定义一个接受隐式参数的函数
 def greetUser(name: String)(implicit greeting: String): Unit = {
   println(s"$greeting, $name!")
 }

 def main(args: Array[String]): Unit = {
   // 定义隐式值
   implicit val greeting: String = "Hello"
   val userName = "Alice"
   // 调用带有显式参数的函数
   greetUser(userName)("Hi")
   // 调用隐式参数的函数，编译器会自动查找并传入隐式值
   greetUser(userName)
 }
}

object ImplicitValueExample {
 // 定义一个接受隐式值的函数
 def greet(implicit greeting: String): Unit = {
   println(greeting)
 }

 // 在对象内部定义隐式值
 implicit val greeting: String = "Bonjour"

 def main(args: Array[String]): Unit = {
   greet // 编译器会查找当前作用域内的隐式值，并传入函数
 }
}

30、定义一个操作符+%，将一个给定的百分比添加到某个值，举例来说，120 +% 10应得到132。定义一个!操作符，计算某个整数的阶乘，举例来说，5!应得到120。提示：由于操作符是方法，而不是函数，使用隐式类来完成。

object Run09 {
 def main(args: Array[String]): Unit = {
   println(120 +% 10)
   println(5.!())
 }
 implicit class compute(a: Int) {
   def +%(b: Int) = a + a * (b / 100.0)

   def !(): Int = {
     if (a == 1) 1
     else a * (a - 1).!()
   }
 }
}

posted @ 2024-06-09 13:14 你这过氧化氢掺水了阅读(88) 评论(0) 编辑收藏举报

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