scala程式設計系列(1)-scala程式設計入門初步
阿新 • • 發佈:2018-12-25
1.scala直譯器
scala與python一樣,可以在終端以直譯器方式互動,只需在終端輸入scala即可
[email protected]:~$ scala
Welcome to Scala version 2.10.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_51).
Type in expressions to have them evaluated.
Type :help for more information.
scala>
在直譯器上可以進行一些簡單的互動,如下:
scala> 1+2 res0: Int = 3 scala> 5+6 res1: Int = 11 scala> 2+3 res2: Int = 5 scala> res3 res4: Int = 5
其資訊的意思為:
res:自動產生的接收結果的變數,並自動編號為res0,res1,res2。冒號(:)後面Int代表型別,等號(=)後面為表示式結果
2.變數定義
scala裡有兩種變數,val和var。val類似於Java裡的final變數,一旦被初始化了就不能再被賦值。var如同普通變數,可以在生命週期內多次賦值。
scala> val msg="Hello World" msg: String = Hello World scala> msg="Hello World again" <console>:8: error: reassignment to val msg="Hello World again"
scala> var msg2="Hello World"
msg2: String = Hello World
scala> msg2="Hello World again"
msg2: String = Hello World again
scala> msg2
res1: String = Hello World again
scala裡面的變數型別一般都是與java相對應的,在賦值時,它可以自動識別為某種型別,我們也可以自己定義變數型別。定義的方式為在變數的後面加上冒號(:)和型別,如:
scala> val msg3:String="Hello World again" msg3: String = Hello World again
3.函式定義
scala> def max(x: Int, y: Int): Int = {
| if (x > y) x
| else y
| }
max: (x: Int, y: Int)Int
scala> max(5,6)
res2: Int = 6
函式的基本結構如下:
但是,這似乎有點複雜,我們可以省略一些不必要的,如省略掉花括號
scala> def max2(x: Int,y: Int) = if (x>y) x else y
max2: (x: Int, y: Int)Int
scala> max2(5,6)
res3: Int = 6
另外還有一種是不帶引數,也不返回有用結果的函式定義
scala> def greet() = println("Hello World!")
greet: ()Unit
scala> greet
Hello World!
scala> greet()
Hello World!
4.編寫scala指令碼
不帶引數的指令碼
[email protected]:~/Mywork/scala$ cat hello.scala
println("Hello world,from a script!")
[email protected]:~/Mywork/scala$ scala hello.scala
Hello world,from a script!
帶引數的指令碼
[email protected]:~/Mywork/scala$ cat helloarg.scala
println("Hello, "+args(0) +"!")
[email protected]:~/Mywork/scala$ scala helloarg.scala Earth
Hello, Earth!
5.while迴圈,if判斷
while迴圈
[email protected]:~/Mywork/scala$ scala printargs.scala Scala is fun
Scala
is
fun
[email protected]:~/Mywork/scala$ cat printargs.scala
var i = 0
while (i < args.length) {
println(args(i))
i += 1
}
更進一步,帶if的,且格式化輸出。
[email protected]:~/Mywork/scala$ scala echoargs.scala Scala is even more fun
Scala is even more fun
[email protected]:~/Mywork/scala$ cat echoargs.scala
var i = 0
while (i < args.length){
if(i != 0)
print(" ")
print(args(i))
i += 1
}
println()
6.for,foreach
用foreach列印引數,非常簡潔
[email protected]:~/Mywork/scala$ scala pa.scala Friday is beautiful
Friday
is
beautiful
[email protected]:~/Mywork/scala$ cat pa.scala
<pre name="code" class="plain">args.foreach(arg => println(arg))
上面pa.scala的完全寫法是
args.foreach((arg:String) => println(arg))
上面foreach括號內是一個函式,其函式標準格式如下(右鍵頭指的方向有點偏)
for迴圈示例
[email protected]:~/Mywork/scala$ scala forargs.scala The Dragon Boat Festival is comming
The
Dragon
Boat
Festival
is
comming
[email protected]:~/Mywork/scala$ cat forargs.scala
for (arg <- args)
println(arg)