Scala中的伴随对象和单例类之间有什么区别（Guice）

Question

I was wondering what was the difference between a companion object and a class declared with @Singleton ?

As I understand, you can only have one instance of both. You can use dependency injection with the class and not with the object but apart from that I don't see much difference to be honest.

Answer 1

Well to put it simply. A singleton object named the same as a class is called a companion object. Also a companion object must be defined inside the same source file as the class. Also are you using Guice ? That @Singleton is a Guice thing i guess.

Answer 2

Very similar stuff. Objects is how Scala allows you to create singleton objects.

Things to keep in mind:

• Singleton classes (Java Style) are easier to test than Objects. This is because you can create different classes in your tests but you can never create more than one Objects
• Objects cannot have a constructor
• Objects cannot be inherited

Answer 3

另一个区别是序列化对Scala单例对象的引用使用自定义代码，该代码将始终解析相应类加载器中存在的该对象的单个实例。

Answer 4

As the name reflects, Singleton in Scala has one instance throughout the application life-cycle. Example of a singleton is Nil which denotes an empty List.

Companion objects on the other hand are helper objects for case classes created in Scala where you can put custom object constructors(apply), implicit conversions, decomposers (unapply). When you define a case class automatically a companion object gets defined.