Created by Wang, Jerry on Sep 25, 2015

application里一個(gè)object extend了一個(gè)App:

通過(guò)查看source code的實(shí)現(xiàn)能發(fā)現(xiàn)App是一個(gè)trait，繼承了DelayedInit:

scala.DelayedInit

Classes and objects (but note, not traits) inheriting the DelayedInit marker trait will have their initialization code rewritten as follows: code becomes delayedInit(code).

Initialization code comprises all statements and all value definitions that are executed during initialization.

Example:

trait Helper extends DelayedInit { def delayedInit(body: => Unit) = { println(“dummy text, printed before initialization of C”) body // evaluates the initialization code of C } } class C extends Helper { println(“this is the initialization code of C”) } object Test extends App { val c = new C }

Should result in the following being printed:

dummy text, printed before initialization of C this is the initialization code of C

所有帶有App 特質(zhì)的類(lèi)，其初始化方法都會(huì)被挪到delayedInit方法中。App特質(zhì)的main方法捕獲到命令行參數(shù)，調(diào)用delayedInit方法。

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