什么是Scala相当于Java的静态块？ [英] What is Scala equivalent of Java's static block?

问题描述

什么是Scala相当于Java的静态块？

What is Scala equivalent of Java's static block ?

推荐答案

构造函数（即正文）中的代码伴随对象不与Java类的静态初始化程序块中的代码完全相同。在下面的示例中，我创建了A的实例，但不会进行初始化。

Code in the constructor (that is, the body) of the companion object is not precisely the same as code in a static initialiser block of a Java class. In the example below, I create an instance of A, but the initialization does not occur.

scala> object Test { class A; object A { println("A.init") }}        
defined module Test

scala> new Test.A
res3: Test.A = Test$A@3b48a8e6

scala> Test.A
A.init
res4: Test.A.type = Test$A$@6e453dd5

要在创建类的第一个实例时触发伴随对象的构造，可以从类构造函数中访问它。

To trigger construction of the companion object when the first instance of the class is created, you could access it from the class constructor.

scala> object Test { class A { A }; object A { println("A.init") }}
defined module Test

scala> new Test.A                                                  
A.init
res5: Test.A = Test$A@4e94a28e

scala> new Test.A
res6: Test.A = Test$A@30227d4e

在很多情况，差异无关紧要。但是如果你发射导弹（或其他副作用），你可能会关心！

In many circumstances, the difference would not matter. But if you are launching missiles (or other side effects), you might care!

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