Scala学习(一)

1.scala面向行的语言,一句是一行的话,末尾的分号可有可无.

2.数据类型: Byte Short Int Long Float Double Char String Boolean,Unit,Nothing,Any,AnyRef

3.变量声明:(声明时必须赋初始值)
    ①变量: var str : String ="Peanut"
            var str ="Peanut" (不指明数据类型也可以,会被推断为String)
            
    ②常量: val num: Int =1
            val num = 1 (不指明数据类型,被推断为Int)
            val a,b =10  (a,b都声明为10)

4.集合(collection):

// 定义整型 List
val x = List(1,2,3,4)

// 定义 Set
val x = Set(1,3,5,7)

// 定义 Map
val x = Map("one" -> 1, "two" -> 2, "three" -> 3)

// 创建两个不同类型元素的元组
val x = (10, "Runoob")

// 定义 Option
val x:Option[Int] = Some(5)

 

5.数组Array:

val arr1=Array(1,2,3)   //val arr1=Array[Int](1,2,3)
    val arr2=Array("a","b","c") //val arr2=Array[String]("a","b","c")   
    val arr3=ArrayBuffer(1,2,3) //val arr3=ArrayBuffer[Int](1,2,3)
    arr3+=4  //ArrayBuffer长度可变,使用+=直接在末尾添加
    val arr4=ArrayBuffer[String]("a","b","c")  //val arr4=ArrayBuffer[String]("a","b","c")
    arr4+=("d","f") 
    val arr5=arr1.toBuffer  //Array转ArrayBuffer
    val arr6=arr3.toArray   //ArrayBuffer转Array
    
    for(ele<-arr1){ print(ele+",")}//一维数组打印
    
    val matrix=ofDim[String](2,3)//二维数组,第一个参数表示外层数组长度,第二个参数表示元素的数组长度
    matrix(0)=Array("a1","b1","c1")
    matrix(1)(0)="a2"
    matrix(1)(1)="b2"
    matrix(1)(2)="c2"
    for(i<- 0 until(mytrix.length)){//二维数组打印
        for(j<- 0 until(mytrix(i).length)){
            print(mytrix(i)(j)+",")
        }
        println()
    }

6.链表List:

 //列表拼接
    List("a","b"):::List("c","d") //List(a,b,c,d)
    List("a","b")++List("c","d")    //List(a,b,c,d)
    List("a","b")++:List("c","d")   //List(a,b,c,d)
    List("a","b")::List("c","d")    //List(List(a, b), c, d)
    List("a","b"):+List("c","d")    //List(a, b, List(c, d))
    //列表长度  length
    List("a","b").length //2
    //****************************
    val fList=List("apple","banana","orange")
    //最后一个元素
    fList.last  //orange
    //除最后一个元素外所有元素
    fList.init  //List("apple","banana")
    //反转
    fList.reverse   //List("orange","banana","apple")
    //取前n个元素
    fList.take(2)   //List("orange","banana")
    //取第n个元素(从0开始)
    fList.apply(2)  //orange
    fList(2)
    //修改第n个元素
    fList.updated(2,"orange2")   //List("apple","banana","orange2")
    //从第n分成两个表
    fList.splitAt(1)    //(List("apple"),List("banana","orage"))
    //除去前n个元素
    fList.drop(2)   //List("orange")
    //***************************************
    val test = List('a','b','c','d','e')
    //元素的索引
    test.indices    //Range(0, 1, 2, 3, 4)
    //索引和元素组成的元组
    test.indices zip test   //Vector((0,a), (1,b), (2,c), (3,d), (4,e))
    //元素和索引组成的List
    test.zipWithIndex   //List((a,0), (b,1), (c,2), (d,3), (e,4))
    //mkString分割
    test.mkString   //abcde
    test.mkString("#")  //a#b#c#d#e
    test.mkString("[","|","]")  //[a|b|c|d|e]
    //grouped分组
    test.grouped(2).mkString(",")   // List(a, b),List(c, d),List(e)
    //************************
    //遍历
    data.foreach{x=>print(x+",")}   //a,b,c,d,e,
    data.map{x=>print(x+",")}   //a,b,c,d,e,

7.映射Map:

  //空哈希表,键为字符串,值为整型
    var A:Map[Char,Int]=Map()
    //Map键值对
    val m1=Map("apple" -> 1,"orange" ->2,"strawberry"->5)
    val m2=Map("apple" -> 3,"banana" ->4)
    //++ Map合并,右边覆盖左边的
    val m3=m1++m2 //Map("apple" -> 3,"orange" ->2,"strawberry"->5,"banana" ->4)
    val m4=m2++m1 //Map("apple" -> 1,"orange" ->2,"strawberry"->5,"banana" ->4)
   
    m1.keys.foreach{i=>
        println("key="+i)
        println("value="+m1(i))
    }