package example
class Apple {
val APPLE_SIZE_KEY: String = "APPLE_SIZE_KEY"
}
课程:
package example
class Store {
fun buy() {
val SIZE = Apple.APPLE_SIZE_KEY
}
}
Error:
'APPLE_SIZE_KEY' has private access in 'example.Apple'
但是official documentation描述了如果我们不指定任何可见性修改器，默认情况下使用public.
Why is above error coming?
What you are trying to do is accessing a value of a class that has no instance. Here are three solutions:
package example
object Apple {
val APPLE_SIZE_KEY: String = "APPLE_SIZE_KEY"
}
This way you do not need to instantiate anything because of the way objects work in Kotlin.
You could also just instantiate your class like this:
package example
class Store {
fun buy() {
val SIZE = Apple().APPLE_SIZE_KEY
}
}
In this solution you also have an object of Apple, but Apple is still declared as a class.
第三个选项是一个伴生对象，其行为类似于Java中的静态变量.
package example
class Apple {
companion object {
val APPLE_SIZE_KEY: String = "APPLE_SIZE_KEY"
}
}