1.Scala 資料型別

Scala 與 Java有著相同的資料型別，下表列出了 Scala 支援的資料型別

Scala的基本資料型別與Java中的基本資料型別是一一對應的，不同的是Scala的基本資料型別頭字母必須大寫

• 整數型別

scala> val intNumber = 10
intNumber: Int = 10

• 浮點型別

// Double型別定義,直接輸入浮點數，編譯器會將其自動推斷為Double型別
scala> val doubleNumber = 3.1415
doubleNumber: Double = 3.1415

scala> val floatNumber = 3.14
floatNumber: Double = 3.14

// 要定義Float型別浮點數，需要在浮點數後面加F或f
scala> val floatNumber = 3.14F
floatNumber: Float = 3.14

scala> val floatNumber = 3.14f
floatNumber: Float = 3.14
 

• 字元

// 字元定義，用''將字元包裹
scala> val charType = 'A'
charType: Char = A

常用特殊字元

• 字串

// 字串變數用""包裹
scala> val helloworld = "hello world"
helloworld: String = hello world

// 要定義"Hello World"，可以加入轉義符\
scala> val helloworld = "\"Hello World\""
helloworld: String = "Hello World"

//如果希望能夠原樣輸出字串中的內容，則用三個引號"""將字串包裹起來
scala> println("""hello world \n hello scala""")
hello world \n hello scala

• 布林型別

scala> val flag = true
flag: Boolean = true

• 變數定義的兩種修飾符
  scala中變數定義有兩種修飾符，一種val，一種是var，兩者區別是val修飾的變數不可變，var修改的變數可變，可再次賦值，以上面定義的helloworld為例

// val 修飾的變數不可再次賦值，否則會報錯 reassignment to val
scala> val hello = "hello"
hello: String = hello

scala> hello = "hello scala"
<console>:12: error: reassignment to val
       hello = "hello scala"
             ^

scala> var hello = "hello"
hello: String = hello

scala> hello = "hello scala"
hello: String = hello scala

2.運算子

2.1 算術操作

例項：

// 整數求和，編譯器會將其轉換為(1).+(2)執行
scala> var sum = 1 + 2
sum: Int = 3

//前一語句等同於下列語句
scala> var sum = (1).+(2)
sum: Int = 3

//操作符過載,編譯器會將其轉換為(1).+(2L)執行
scala> var longSum = 1 + 2L
longSum: Long = 3

// 減法
scala> var jian = 1-5
jian: Int = -4

// 除法
scala> val chu = 1/5
chu: Int = 0

// 取模
scala> val mo = 1%5
mo: Int = 1

// 乘法
scala> val cheng = 1L * 5L
cheng: Long = 5

// scala中可以用+ -符號來表示正負數，例如-3 +3，並且可以加入到運算子當中
scala> val num = 1 + -5
num: Int = -4

2.2 關係運算

例項：

scala> 5 > 1
res1: Boolean = true

scala> 5 < 1
res2: Boolean = false

scala> 5 <= -1
res3: Boolean = false

scala> 5 <= 10
res4: Boolean = true

// "!" 表示求反
scala> !(5 <= -5)
res5: Boolean = true

scala> 5 != -5
res6: Boolean = true

scala> 5 == 5
res7: Boolean = true

2.3 邏輯運算

例項：

scala> val a = true
a: Boolean = true

scala> val b = false
b: Boolean = false

scala> a && b
res8: Boolean = false

scala> a || b
res9: Boolean = true

scala> !(a || b)
res10: Boolean = false

scala> a && !b
res11: Boolean = true

##2.4 賦值運算子

例項：

object Test {
  def main(args: Array[String]): Unit = {
    var a = 2;
    var b = 5;
    var c = 0;

    c += b
    println("c += b = " + c) // c += b = 5

    c -= a
    println("c -= a = " + c) // c -= a = 3

    c *= 5
    println("c *= 5 = " + c) // c *= 5 = 15

    c /= b
    println("c /= a = " + c) // c /= a = 3

    c %= a
    println("c %= a = " + c) // c %= a = 1
  }
}

3. 流程控制

• if使用

scala> val num = if("hello"=="hello") 1 else 0
num: Int = 1

• while使用

scala> var a = 1
a: Int = 1

scala> while(a <= 10) {
     | println("a = " + a)
     | a += 1
     | }
a = 1
a = 2
a = 3
a = 4
a = 5
a = 6
a = 7
a = 8
a = 9
a = 10

• do while 使用

scala> do{
     | println("a = " + a)
     | a += 1
     | } while(a <= 10)
a = 1
a = 2
a = 3
a = 4
a = 5
a = 6
a = 7
a = 8
a = 9
a = 10

• for使用

// 1 to 10 表示1到10
scala> for(a <- 1 to 10){
     | println("a = " + a)
     | }
a = 1
a = 2
a = 3
a = 4
a = 5
a = 6
a = 7
a = 8
a = 9
a = 10

// 1 until 10 表示1到10但不包括10
scala> for(a <- 1 until 10){
     | println("a = " + a)
     | }
a = 1
a = 2
a = 3
a = 4
a = 5
a = 6
a = 7
a = 8
a = 9

// 在 for 迴圈 中你可以使用分號 (;) 來設定多個區間，它將迭代給定區間所有的可能值
scala> for(a <- 1 to 3; b <- 1 to 3){
     | println("a = " + a)
     | println("b = " + b)
     | }
a = 1
b = 1
a = 1
b = 2
a = 1
b = 3
a = 2
b = 1
a = 2
b = 2
a = 2
b = 3
a = 3
b = 1
a = 3
b = 2
a = 3
b = 3

// 可以將 for 迴圈的返回值作為一個變數儲存。語法格式如下：
var retVal = for{ var x <- List
     if condition1; if condition2...
}yield x
// 大括號中用於儲存變數和條件，retVal 是變數，迴圈中的 yield 會把當前的元素記下來，儲存在集合中，迴圈結束後將返回該集合
例項：
scala> var a = 0
a: Int = 0

scala> val numList = List(1,2,3,4,5,6,7,8,9,10)
numList: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> var retVal = for{ a<- numList if a != 3; if a < 8 } yield a
retVal: List[Int] = List(1, 2, 4, 5, 6, 7)

scala> for(a <- retVal){
     | println("a = " + a)
     | }
a = 1
a = 2
a = 4
a = 5
a = 6
a = 7