Scala Apply Method Notes

There is such a cluster class in the Akka source code.

The way to use this is: Val cluster = cluster (Context.system);

As a novice in Scala, I did not find cluster (System..) This is a constructive method of the argument. Then he started to learn Scala.

Cluster is an object singleton.

One aspect of Scala that is more object-oriented than Java is that Scala has no static members. The alternative is that Scala has a singleton: Singleton object.

When a singleton object shares the same name as a class, he is referred to as the associated object of the class: companion object. You must define the class and its associated objects in the same source file. The class is referred to as the associated class for this Singleton object: Companion class. The class and its associated objects can access each other's private members.

Define a singleton object that is not a definition type (at the level of Scala's abstraction)

One difference between a class and a singleton object is that the singleton object has no arguments, and the class can. Because you cannot instantiate a singleton object with the New keyword, you do not have the opportunity to pass it arguments. Each singleton object is implemented as a fictitious class that is pointed to by a static variable: an instance of the synthetic class, so they have the same initialization syntax as the Java static class. The Scala program specifically points out that a singleton object is initialized when it is first accessed.

Scala's apply has 2 forms, one is the associated object of apply, one is the associated class of apply, the following shows the use of the 2 in the apply.

Example code:

Class Applyoperation {}class applytest{    def apply () = println ("I am into the spark so much!!!")    def haveatry:unit ={        println ("has a try on apply")    }}object applytest{     def apply () = {          println ("I  A M into Scala so much ")        new applytest     }}object applyoperation{     def main (args:array[string]) {        Val Array = Array (1,2,3,4)        val a = Applytest ()//This is the use of object         a.haveatry         A ()//Here is the class in the Apply    }}

Run results

I am into the Scala so much
There is a try on apply
I am into the spark so much!!!

Object apply is a more common use. Mainly used to solve the problem of initialization of complex objects. It is also a single case.

(Just like the Singleton factory method in Java)

(go) Scala apply method notes