[FIXED] What does this Spring Component and Kotlin Class consist of?

Issue

I have this class here:

@Component
class UpdateRule(
  private val rulesRepo: UpdateRuleRepo
) : UpdateRuleStoreGateway, UpdateRuleLoadGateway {

  override fun store(rule: UpdatRule) {
        //some code
  }

  override fun loadAll(): List<UpdateRule> {
        //some code
  }

Since I'm new to Spring and Kotlin, I'm not familiar with this syntax. What does the val inside the brackets mean (private val rulesRepo: UpdateRuleRepo) and what do the interfaces after the colon do (: UpdateRuleStoreGateway, UpdateRuleLoadGateway)? Is this Kotlin specific or Spring specific syntax and where can I read more about it?

Solution

This is Kotlin syntax, not Spring-specific.

What does the val inside the brackets mean (private val rulesRepo: UpdateRuleRepo)

The part between the parentheses () is the list of arguments for the primary constructor of the class. When a constructor argument is marked val or var, it also declares a property of the same name on the class.

In this case, it means rulesRepo is a constructor argument of the class UpdateRule, but also a property of that class. Since it's a val, it means the property is read-only (it only has a getter).

You can read more about this in the docs about constructors.

what do the interfaces after the colon do (: UpdateRuleStoreGateway, UpdateRuleLoadGateway)?

The types listed after the : in a class declaration are the parent classes (or interfaces) extended (or implemented) by that class. In this case it means UpdateRule implements both interfaces UpdateRuleStoreGateway and UpdateRuleLoadGateway.

This is described in the docs about implementing interfaces.

Answered By - Joffrey