scala编程系列(1)-scala编程入门初步
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1.scala解释器
scala与python一样,可以在终端以解释器方式交互,只需在终端输入scala即可
jpan@jpan-Beijing:~$ scalaWelcome 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>
在解释器上可以进行一些简单的交互,如下:
scala> 1+2res0: Int = 3scala> 5+6res1: Int = 11scala> 2+3res2: Int = 5scala> res3res4: Int = 5
其信息的意思为:
res:自动产生的接收结果的变量,并自动编号为res0,res1,res2。冒号(:)后面Int代表类型,等号(=)后面为表达式结果
2.变量定义
scala里有两种变量,val和var。val类似于Java里的final变量,一旦被初始化了就不能再被赋值。var如同普通变量,可以在生命周期内多次赋值。
scala> val msg="Hello World"msg: String = Hello Worldscala> msg="Hello World again"<console>:8: error: reassignment to val msg="Hello World again"
scala> var msg2="Hello World"msg2: String = Hello Worldscala> msg2="Hello World again"msg2: String = Hello World againscala> msg2res1: String = Hello World again
scala里面的变量类型一般都是与java相对应的,在赋值时,它可以自动识别为某种类型,我们也可以自己定义变量类型。定义的方式为在变量的后面加上冒号(:)和类型,如:
scala> val msg3:String="Hello World again"msg3: String = Hello World again
3.函数定义
scala> def max(x: Int, y: Int): Int = { | if (x > y) x | else y | }max: (x: Int, y: Int)Intscala> max(5,6)res2: Int = 6
函数的基本结构如下:
但是,这似乎有点复杂,我们可以省略一些不必要的,如省略掉花括号
scala> def max2(x: Int,y: Int) = if (x>y) x else ymax2: (x: Int, y: Int)Intscala> max2(5,6)res3: Int = 6另外还有一种是不带参数,也不返回有用结果的函数定义
scala> def greet() = println("Hello World!")greet: ()Unitscala> greetHello World!scala> greet()Hello World!
4.编写scala脚本
不带参数的脚本
jpan@jpan-Beijing:~/Mywork/scala$ cat hello.scala println("Hello world,from a script!")jpan@jpan-Beijing:~/Mywork/scala$ scala hello.scala Hello world,from a script!带参数的脚本
jpan@jpan-Beijing:~/Mywork/scala$ cat helloarg.scala println("Hello, "+args(0) +"!")jpan@jpan-Beijing:~/Mywork/scala$ scala helloarg.scala EarthHello, Earth!
5.while循环,if判断
while循环
jpan@jpan-Beijing:~/Mywork/scala$ scala printargs.scala Scala is funScalaisfunjpan@jpan-Beijing:~/Mywork/scala$ cat printargs.scala var i = 0while (i < args.length) { println(args(i)) i += 1}更进一步,带if的,且格式化输出。
jpan@jpan-Beijing:~/Mywork/scala$ scala echoargs.scala Scala is even more funScala is even more funjpan@jpan-Beijing:~/Mywork/scala$ cat echoargs.scala var i = 0while (i < args.length){ if(i != 0) print(" ") print(args(i)) i += 1}println()
6.for,foreach
用foreach打印参数,非常简洁
jpan@jpan-Beijing:~/Mywork/scala$ scala pa.scala Friday is beautifulFridayisbeautifuljpan@jpan-Beijing:~/Mywork/scala$ cat pa.scala <pre name="code" class="plain">args.foreach(arg => println(arg))
上面pa.scala的完全写法是
args.foreach((arg:String) => println(arg))上面foreach括号内是一个函数,其函数标准格式如下(右键头指的方向有点偏)
for循环示例
jpan@jpan-Beijing:~/Mywork/scala$ scala forargs.scala The Dragon Boat Festival is commingTheDragonBoatFestivaliscommingjpan@jpan-Beijing:~/Mywork/scala$ cat forargs.scala for (arg <- args) println(arg)
0 0
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