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

Big data, a good programmer, shares scala singletons and concomitant objects along the learning route.

Scala singleton

Object SingletonDemo {

Def main (args: Array [String]): Unit = {

Val s = SessionFactory

Println (s.getSession)

Println (s.getSession.size) / / .size gets several session objects

}

}

Object SessionFactory {

Println ("SessionFactory is executed")

/ / counter

Var I = 5

/ / an array of session objects

Val sessions = new ArrayBuffer [Session] ()

While (I > 1) {

Println ("while is executed")

Sessions.append (new Session)

I-= 1

}

/ / get the session object

Def getSession = sessions

}

Class Session {

}

Associated object

Singleton objects include concomitant objects, and classes and companion objects can access each other, even private fields and properties modified by private

The concomitant object is first of all a singleton object, which is defined by object.

In scala, there are two kinds of singleton objects

1. An association is not automatically associated with a singleton object of a particular class, called a stand-alone object-> Standalone Object

two。 A singleton object associated with a class that has the same class name as the class and is called accompanying object-> Companion Object

Class companionObject {

Var id = 0

Privateval name = "zhaoxiaodan"

Def printContent () = {

Println (name+companionObject.Constant)

}

}

Object companionObject {

Privateval Constant = "is my goddess"

Def main (args: Array [String]): Unit = {

Val co = new companionObject

Co.id = 8

Println (co.id)

Println (co.name)

Co.printContent () / / zhaoxiaodan is my goddess

}

}

Apply and unapply (usually define the apply method in the companion object of the class)

The apply method, often referred to as the injection method, does an initialization operation in the accompanying object of the class

The parameter list of the apply method does not need to be unified with the main constructor list

The unapply method is usually an extraction method, and the unapply method can be used to extract a fixed number of objects and values in the constructor.

The unapply method returns an Option, and if there are values in the Option, there is an internal some object that encapsulates these values.

Class ApplyDemo (val name: String, val age: Int, val faceValue: Int) {

}

Object ApplyDemo {

/ / injection method

Def apply (name: String, age: Int): ApplyDemo = {

New ApplyDemo (name,age,faceValue = 80) / / initialization

}

/ / extraction method

Def unapply (applyDemo: ApplyDemo): Option [(String,Int,Int)] = {

If (applyDemo = = null) {

None

} else {

Some (applyDemo.name,applyDemo.age,applyDemo.faceValue)

}

}

}

Object ApplyTest {

Def main (args: Array [String]): Unit = {

Val applyDemo = ApplyDemo (Zhao Xiaodan, 18)

ApplyDemo match {

Case ApplyDemo (Zhao Xiaodan, age,faceValue) = > println (s "name: Zhao Xiaodan, age:$age,fv:$faceValue")

Case _ = > println ("is null")

}

}

}

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