学习scala笔记--18 scala 函数基础

 

 

 

 

scala  函数编程

 

 

 

 

 

scala 中的函数式一等公民   可以独立存在   可以将函数作为值赋给变量

 

 

scala> def sayHello(name:String) {println(" hello "+name)}

sayHello: (name: String)Unit

 

scala> sayHello("cat")

 hello cat

 

注意这里的 空格 下划线

scala> val sayHelloFunc = sayHello _

sayHelloFunc: String => Unit = $$Lambda$1210/524541191@26db2470

 

 

scala> sayHelloFunc(" hadoop ")

 hello  hadoop 

 

 

 

 

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匿名函数

 

注意这里的 =>

 

scala> val helloFunc = (name:String)=>{ println("--hello--"+name)}

helloFunc: String => Unit = $$Lambda$1221/1679266544@472bf56c

 

scala> helloFunc(" scala ")

--hello-- scala 

 

scala> 

 

 

 

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高阶函数  

 

接收函数作为参数

 

scala> val helloFunc = (name:String)=>{ println("--hello--"+name)}

helloFunc: String => Unit = $$Lambda$1222/1726168677@2c3d1e97

 

scala> def greeting(func:(String)=> Unit ,name:String){ func(name)}

greeting: (func: String => Unit, name: String)Unit

 

scala> greeting(helloFunc," hive ")

--hello-- hive 

 

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函数的返回值 为函数

 

scala> def mulBy(factor:Double)=(x:Double)=>factor*x

mulBy: (factor: Double)Double => Double

 

scala> val mulBy2 = mulBy(2)

mulBy2: Double => Double = $$Lambda$1350/973028061@775d7f5d

 

scala> mulBy2(1)

res18: Double = 2.0

 

scala> mulBy2(2)

res19: Double = 4.0

 

scala> mulBy2(3)

res20: Double = 6.0

 

 

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