scala编程系列(1)-scala编程入门初步

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:~$ 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>

在解释器上可以进行一些简单的交互，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 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)Int

scala> 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 y
max2: (x: Int, y: Int)Int

scala> 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: ()Unit

scala> greet
Hello 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 Earth
Hello, Earth!

5.while循环，if判断

while循环

jpan@jpan-Beijing:~/Mywork/scala$ scala printargs.scala Scala is fun
Scala
is
fun

jpan@jpan-Beijing:~/Mywork/scala$ cat printargs.scala
var i = 0
while (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 fun
Scala is even more fun
jpan@jpan-Beijing:~/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打印参数，非常简洁

jpan@jpan-Beijing:~/Mywork/scala$ scala pa.scala Friday is beautiful
Friday
is
beautiful

jpan@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 comming
The
Dragon
Boat
Festival
is
comming
jpan@jpan-Beijing:~/Mywork/scala$ cat forargs.scala
for (arg <- args)
println(arg)