2、基础

快捷功能

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补全　　Tab键

粘贴模式　　:paste，退出粘贴模式 ctrl + d

语法

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var　　定义变量

val　　定义常量，相当于java中的final，不能重复赋值

1 to 10　　[ 1, 10 ]

1 until  10　　[ 1,10 )

字符串求交集

scala> "hello".intersect("he")
res31: String = he

BigInt类型

scala> var b = BigInt(999999999)
b: scala.math.BigInt = 999999999

scala> b *= b　　　　//scala中没有 ++ 或 -- 语法

scala> b
res33: scala.math.BigInt = 999999998000000001

scala> b *= b

scala> b
res35: scala.math.BigInt = 999999996000000005999999996000000001

导包

import scala.math._　　//此处 _ 表示所有
sqrt(2)               //开方
pow(2,3)              //幂函数

apply方法，相当于索引

scala> "hello".apply(2)
res40: Char = l

scala> "hello"(2)
res41: Char = l

scala中表达式都有值

scala> var x = 2
x: Int = 2

scala> var y = if(x > 0) 1 else -1
y: Int = 1

scala> var y = if(x < 0) -1
y: AnyVal = ()

scala> var p = println(123)
123
p: Unit = ()　　//相当于null

最后一个表达式是整个语句的值

scala> var b = {print() ;234}
warning: there was one deprecation warning; re-run with -deprecation for details
()b: Int = 234

输入

scala> var name = readLine("输入名字：")
warning: there was one deprecation warning; re-run with -deprecation for details
输入名字：name: String = lasdjfonclnvlolfdgolsdfsadfs

scala> name
res43: String = lasdjfonclnvlolfdgolsdfsadfs

循环：while、for、for高级用法

break

scala> import scala.util.control.Breaks._
import scala.util.control.Breaks._

scala> for(i <- 1 to 10){
     | println(i)
     | break}
1
scala.util.control.BreakControl

scala>

 yield

scala> for(i <- 1 to 5)yield i*3
res6: scala.collection.immutable.IndexedSeq[Int] = Vector(3, 6, 9, 12, 15)

函数

object Demo  {
  def main(args: Array[String]): Unit = {
    //阶乘：非递归和递归
    val f1 = fact(5)
    val f2 = fact2(5)

    //方法：默认参数，使用：有名参数
    val s1 = decorate1("{{","hello","}}")
    val s2 = decorate2(str="hello")
    val s3 = decorate3("hello")

    //变长参数
    val v1 = varPar(1,2,3,4,5)
    val v2 = varPar(0 to(10,2):_*) //将Range对象展开成0，2，4，6，8，10的序列

    //过程,即没有 =
    val g = out(1,2,3)  // ()
  }

  //阶乘
  def fact(n:Int)={
    var f = 1
    for (i <- 1 to n)f *= i
    f
  }
  //阶乘：递归，注意：需要显示定义结果类型
  def fact2(n:Int):Int={
    if (n == 1) 1 else n*fact2(n-1)
  }

  //默认参数
  def decorate1(prefix:String,str:String,suffix:String)={
    prefix + str + suffix
  }
  def decorate2(prefix:String="[",str:String,suffix:String="]")={
    prefix + str + suffix
  }
  def decorate3(str:String,prefix:String="(",suffix:String=")")={
    prefix + str + suffix
  }

  //变长参数
  def varPar(n:Int*)=n.sum

  //过程
  def out(n:Int*){n.sum}
}

lazy，延迟计算，调用时才计算

scala> val x = 1/0
java.lang.ArithmeticException: / by zero
  ... 32 elided

scala> lazy val x = 1/0
x: Int = <lazy>

scala> x
java.lang.ArithmeticException: / by zero
  at .x$lzycompute(<console>:14)
  at .x(<console>:14)
  ... 32 elided

scala中 _ 线含义

　　1、import scala.math._　　所有类似 *

　　2、Range对象展开成数字序列

scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer

scala> val arr = ArrayBuffer(1)
arr: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1)

scala> arr.append(1 to 3:_*)

scala> arr
res6: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 1, 2, 3)

　　3、取出元组元素，索引从1开始

scala> val t = ("qq","ww")
t: (String, String) = (qq,ww)

scala> t._1
res9: String = qq

scala> t._2
res10: String = ww

　　4、取出函数本身

scala> val f = scala.math.ceil _
f: Double => Double = <function1>

　　5、模式匹配中的其他，相当于java中switch-case语句中的default

　　　　val ch = 'c'
        ch match {
            case 'a' => println(1)
            case 'b' => println(2)
            case  _  => println(3)
        }

　　6、变量默认值

　　　　var s:String = _ 

apply 用法

　　1、取索引

scala> "12345"(2)
res0: Char = 3

scala> "12345".apply(2)
res1: Char = 3

　　2、初始化

scala> val arr = Array.apply[Int](1,2,3)
arr: Array[Int] = Array(1, 2, 3)

scala> val arr = Array.apply(1,2,3)
arr: Array[Int] = Array(1, 2, 3)

scala> val arr = Array(1,2,3)
arr: Array[Int] = Array(1, 2, 3)

scala中继承层级

　　AnyVal：  root class of all ''value types''

 Double、Float、Long、Int、Char、Short、Byte：'numeric value types'Unit、Boolean：'non-numeric value types'

　　Unit 只有一个值用 () 表示，相当于java中void

       Null 类型只有一个实例 null

       Nothing 类型没有实例，是任何类型子类型

其他

Option子类型：None 和 Some

Nil 空列表，类型List[Nothing]