1 if表达式
- Scala中if...else..表达式是有返回值的,如果if和else返回值类型不一样,则返回Any类型。
scala> val a3=10
a3: Int = 10scala> val a4=
| if(a3>20){
| "a3大于a4"
| }else{
| "a4大于a3"
| }
a4: String = a4大于a3scala> val a5=
| if(a3>20)"a3大于20"
a5: Any = ()scala> println(a5)
()
2 while表达式
- while循环
scala> def gcdLoop(x:Long,y:Long):Long={| var a=x| var b=y| while(a!=0){| val temp=a| a=b%a| b=temp| }| b| }
gcdLoop: (x: Long, y: Long)Longscala> gcdLoop(8,9)
res0: Long = 1scala> gcdLoop(8,4)
res1: Long = 4
- while循环的中断
import scala.util.control.Breaks
object whilexample {def main(args:Array[String]): Unit ={var n=1;val loop=new Breaksloop.breakable{while(n<=20){n+=1;if(n==19){loop.break()}}}println(n)}
}
结果如下:
3 for表达式
- for中to示例:
scala> for(i <- 1 to 3; j <- 1 to 3){| print(i * j + " ")| }
1 2 3 2 4 6 3 6 9
- for中until示例:
scala> for(i <- 1 until 3; j <- 1 until 3) {| print(i * j + " ")| }
1 2 2 4
- for中的条件判断示例
scala> for(i <- 1 to 3 if i != 2) {| print(i+" ")| }
1 3
scala>
- for中的引入变量
scala> for(i <- 1 to 3; j = 4 - i) {| print(j+" ")| }
3 2 1
- 使用yield关键字,将遍历过程处理结果返回一个值。
scala> val for5 = for(i <- 1 to 10) yield i
for5: scala.collection.immutable.IndexedSeq[Int] = Vector(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)scala> print(for5)
Vector(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
scala> val for5 = for(i <- 1 to 10)| print(for5)
<console>:13: error: recursive value for5 needs typeprint(for5)^
- 过滤,通过for中的() 添加过滤器(filter),就是if子句。
object hello{def main(args:Array[String]){ val filesHere=(new java.io.File(".")).listFilesfor(file<-filesHere if(file.getName.endsWith(".scala")))println(file)}}D:\>scala hello.scala
.\a.scala
.\h.scala
.\hello.scala
.\s.scala
4 try表达式
- 抛出异常
scala> def ha(n:Int){| val half=if(n%2==0) print(n/2)| else| throw new RuntimeException("n num be even")| }
ha: (n: Int)Unitscala> ha(7)
java.lang.RuntimeException: n num be evenat .ha(<console>:14)... 28 elidedscala> ha(8)
4
- 捕获异常
捕获异常的语法选择catch子句的原因是与模式匹配保持一致。
object ExceptionSyllabus {def divider(x: Int, y: Int): Float= {if(y == 0) throw new Exception("0作为了除数")else x / y}def main(args: Array[String]): Unit = {try {println(divider(10, 3))} catch {case ex: Exception => println("捕获了异常:" + ex)} finally {}}}D:\>scala ExceptionSyllabus.scala
3.0//当数字改为(10,0)后
D:\>scala ExceptionSyllabus.scala
捕获了异常:java.lang.Exception: 0作为了除数
5 匹配表达式
- Scala中的match表达式类似于其它语言的switch语句,它可用提供多个备选项做选择。
object frist{def main(args:Array[String]){ val firstArg=if(args.length>0)args(0) else ""firstArg match{case "salt"=>println("papper")case "chips"=>println("salsa")case "eggs"=>println("bacon")case _=>println("huh?")}}}D:\>scala frist.scala
huh?D:\>scala frist.scala salt
papper
6 lazy懒值
- 当val被声明为lazy时,初始化将被推迟,直到我们首次对此取值,适用于初始化开销较大的场景。 通过lazy关键字的使用与否,来观察执行过程
object Lazy {def init(): String = {println("init方法执行")"嘿嘿嘿,我来了~"}def main(args: Array[String]): Unit = {lazy val msg = init()println("lazy方法没有执行")println(msg)}}
结果:
object Lazy {def init(): String = {println("init方法执行")"嘿嘿嘿,我来了~"}def main(args: Array[String]): Unit = {val msg = init()println("lazy方法没有执行")println(msg)}}
结果:
7 柯里化
在函数编程中,将接受多个参数的函数转化为接受单个参数的函数。这一过程称为柯里化
scala> def mul(x: Int, y: Int) = x * y
mul: (x: Int, y: Int)Intscala> println(mul(10, 10))
100scala> def mulCurry(x: Int) = (y: Int) => x * y
mulCurry: (x: Int)Int => Intscala> println(mulCurry(10)(9))
90scala> def mulCurry2(x: Int)(y:Int) = x * y
mulCurry2: (x: Int)(y: Int)Intscala> println(mulCurry2(10)(8))
80
- 柯里化的应用:在忽略大小写的情况下,计较是否相等。
scala> val a = Array("Hello", "World")
a: Array[String] = Array(Hello, World)scala> val b = Array("hello", "world")
b: Array[String] = Array(hello, world)scala> println(a.corresponds(b)(_.equalsIgnoreCase(_)))
true