Visibility modifiers

When you define your class, contained methods, properties, or fields can have various visibility levels. In Kotlin, there are four possible values:

• Public: This can be accessed from anywhere
• Internal: This can only be accessed from the module code
• Protected: This can only be accessed from the class defining it and any derived classes
• Private: This can only be accessed from the scope of the class defining it

If the parent class specifies that a given field is open for being redefined (overwritten), the derived class will be able to modify the visibility level. Here is an example:

    open class Container { 
      protected open val fieldA: String = "Some value" 
    } 
    class DerivedContainer : Container() { 
      public override val fieldA: String = "Something else" 
    } 

Now in the main class, you can create a new DerivedContainer...