Shulou(Shulou.com)06/03 Report--

Good programmer big data tutorials share the Option_ partial function of Scala series _ String

Option Typ

In Scala, the Option type sample class is used to represent values that may or may not exist (subclasses of Option are Some and None). Some wraps a value, and None means no value.

Object OptionDemo {

Def main (args: Array [String]) {

Val map = Map ("a"-> 1, "b"-> 2)

Val v = map.get ("b") match {

Case Some (I) = > I

Case None = > 0

}

Println (v)

/ / A better way

Val v1 = map.getOrElse ("c", 0)

Println (v1)

}

}

Partial function

A set of case statements that are wrapped without match in curly braces is a partial function, which is an instance of PartialFunction [A, B], where A represents the parameter type and B represents the return type, often used as an input pattern match

Object PartialFunctionDemo {

Def f: PartialFunction [String, Int] = {

Case "one" = > 1

Case "two" = > 2

/ / case _ = >-1

}

Def main (args: Array [String]) {

/ / call f.apply ("one")

Println (f ("one"))

Println (f.isDefinedAt ("three"))

/ / throw MatchError

Println (f ("three"))

}

} String INTERPOLATION (string interpolation) (alternative)

Purpose: dealing with string types:

S: string interpolation

F: interpolate and format the output

Raw: output without any transformation on the string

After Scala 2. 10. 0, a new mechanism for creating strings, String Interpolation. 0, is introduced. It allows the user to embed a reference to a variable directly in a string.

Val name= "James"

Println (s "Hello,$name") / / Hello, James

The position of string interpolation can also be expressed as follows:

Println (s "1 + 1 = ${1 + 1}") / / 1 + 1 = 2

Interpolation f can format strings, similar to printf:

Val height = 1.9d

Val name = "James"

Println (f "$name%s is $height%2.2f meters tall") / / James is 1.90 meters tall

Raw is similar to s, but raw does not convert the contents of the string:

Scala > s "a\ nb"

Res0: String =

A

B

Scala > raw "a\ nb"

Res1: String = a\ nb

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