Scala课程04

核心内容: 
1、Scala数组操作实战详解

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知识点: 
(1)静态数组使用Array进行创建、动态数组使用ArrayBuffer进行创建 
(2)用户提供初始值时不要使用new 
(3)scala中的yield的主要作用是记住每次迭代中的有关值,并逐一存入到一个数组中. 
示例程序:

                                                                                 scala中数组的常见操作

 

object ScalaAction1
{
     println("Welcome to the Scala worksheet")    //> Welcome to the Scala worksheet
     //定义静态数组
     val a1 = new Array[Int](3)                   //> a1  : Array[Int] = Array(0, 0, 0)
     val a2 = new Array[String](3)                //> a2  : Array[String] = Array(null, null, null)
     val a3 = Array[Int](20,30,40)                //> a3  : Array[Int] = Array(20, 30, 40)
     a3(1) = 100
     for(ele<- a3) println(ele)                   //> 20
                                                  //| 100
                                                  //| 40
    //定义动态数组的两种方式
    import scala.collection.mutable.ArrayBuffer
    val a4 = new ArrayBuffer[Double]()            //> a4  : scala.collection.mutable.ArrayBuffer[Double] = ArrayBuffer()
    val a5 = ArrayBuffer[Double](23.0,52.0)       //> a5  : scala.collection.mutable.ArrayBuffer[Double] = ArrayBuffer(23.0, 52.0)
                                                  //| 
    //动态数组的一些基本操作
    val a6 =  ArrayBuffer[Int]()                  //> a6  : scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()
    a6 += 10                                      //> res0: IT.ScalaAction1.a6.type = ArrayBuffer(10)
    a6 += (20,30)                                 //> res1: IT.ScalaAction1.a6.type = ArrayBuffer(10, 20, 30)
    a6 ++= Array(40,50,60)                        //> res2: IT.ScalaAction1.a6.type = ArrayBuffer(10, 20, 30, 40, 50, 60)
    a6                                            //> res3: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(10, 20, 30, 40
                                                  //| , 50, 60)
    a6.trimEnd(2)
    a6                                            //> res4: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(10, 20, 30, 40
                                                  //| )

    a6.insert(1,100,200)
    a6                                            //> res5: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(10, 100, 200, 
                                                  //| 20, 30, 40)
    a6.remove(2)                                  //> res6: Int = 200
    a6                                            //> res7: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(10, 100, 20, 3
                                                  //| 0, 40)
    val a7 = a6.toArray                           //> a7  : Array[Int] = Array(10, 100, 20, 30, 40)
    //遍历数组的两种方式
    for(ele<- a7) println(ele)                    //> 10
                                                  //| 100
                                                  //| 20
                                                  //| 30
                                                  //| 40
    for(i<- 0 until a7.length) println(a7(i))     //> 10
                                                  //| 100
                                                  //| 20
                                                  //| 30
                                                  //| 40
    //yield的用法
    val a8 = for(ele<- a7) yield ele*2            //> a8  : Array[Int] = Array(20, 200, 40, 60, 80)
    val a9 = for(ele<- a7;if(ele%20 == 0)) yield ele*2
                                                  //> a9  : Array[Int] = Array(200, 40, 80)
    val a10 = a7.filter(_%20==0).map(2*_)         //> a10  : Array[Int] = Array(200, 40, 80)

    //对数组常用的算法操作
    val sum = Array(10,20,30).sum                 //> sum  : Int = 60
    val maxnum = Array(10,20,30).max              //> maxnum  : Int = 30
    val str2 =  ArrayBuffer("zh","ming","abcde").max
                                                  //> str2  : String = zh
    //排序之后返回一个新的数组
    val a11 = a7.sorted                           //> a11  : Array[Int] = Array(10, 20, 30, 40, 100)
    a7                                            //> res8: Array[Int] = Array(10, 100, 20, 30, 40)
    //对动态数组内部进行排序,不返回新的数组
    scala.util.Sorting.quickSort(a7)
    a7                                            //> res9: Array[Int] = Array(10, 20, 30, 40, 100)

    //指定分隔符,将数组中的元素连接起来
    val str3 = a7.mkString(" and ")               //> str3  : String = 10 and 20 and 30 and 40 and 100
    val str7 = a7.mkString("\t")                  //> str7  : String = 10   20  30  40  100
    val str8 = a7.mkString("<",",",">")           //> str8  : String = <10,20,30,40,100>
    //定义二元数组的方式
    val matrix =  Array.ofDim[Double](2,3)        //> matrix  : Array[Array[Double]] = Array(Array(0.0, 0.0, 0.0), Array(0.0, 0.0
                                                  //| , 0.0))
    matrix(1)(0) = 10.0
    matrix                                        //> res10: Array[Array[Double]] = Array(Array(0.0, 0.0, 0.0), Array(10.0, 0.0, 
                                                  //| 0.0))
}