2.scala控制结构、函数、异常处理---小书匠,在线编辑器,MARKDOWN,Evernote,文件版本 input{
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Orginal Style from ethanschoonover.com/solarized (c) Jeremy Hull
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2.scala控制结构、函数、异常处理
2.1条件表达式
(1)if表达式有返回值,如val result = if(x>0) 0 else -1 ,则result值可能为0或-1
(2)if表达式分支语句返回值的类型不一致时,则表达式返回值的类型是它们共同的父类型Any
val result = if(x>0) 0 else "error"
则result的类型为Any
(3)若if表达式没有分支满足条件,则返回Unit
2.2块表达式
(1)块表达式的值是最后一个语句的返回值,一个块中有多个语句时用逗号隔开。如:
val result = {val x=2;val y=3;pow(x,y)}
2.3循环
(1)while循环的实现方式和java中一样。
(2)scala中的for循环写法如下:
for(i <- 1 to 10){ println(i) }
(3)for推导式。如果for循环的循环体以yield开始,则该循环会构造出一个集合,每次迭代生成集合中的一个值,如:
for(i <- 1 to 10) yield i%3 //得到Vector(1,2,0,1,2,0,1,2,0,1)
2.4函数
一个函数包含了函数名称,参数和函数体等三个元素,如:
def abs(x:Double) = if(x>=0) x else -x
如果不是递归函数,不需要给定返回值类型
2.5参数
(1)默认参数。调用某些函数时可以不用给出参数,此时使用默认参数。如:
def check(path:String,name:String="home")
使用check("local")时传入的两个参数分别为local和默认的home
(2)带名参数。在提供参数值的时候指定参数名,带名参数可以打乱参数列表的顺序,但是带名参数和不带名参数共同使用时,需要将不带名参数放在带名参数之前。
(3)变长参数。参数列表可以为同类型的多个参数。如:
def sum(num:Int*)={ val count = 0 for(i <-num){ count +=i } }
函数得到的是一个序列,但是不代表可以传入一个序列。如sum(1 to 5)这种写法是错误的。
2.6懒值
当val被生命为lazy时,它的初始化会被推迟,直到其被第一次取值时。如:
val a = 0 lazy val b = a*10
2.7异常处理
scala中异常处理与java类似。一般写法如下:
try{ process }catch{ case e:Throwable => some process case _ => other process }finally{ }
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