I am new to Kotlin and I am confused between open
and public
keywords. Could anyone please tell me the difference between those keywords?
问题:
回答1:
The open
keyword means “open for extension“:
The
open
annotation on a class is the opposite of Java'sfinal
: it allows others to inherit from this class. By default, all classes in Kotlin arefinal
, which corresponds to Effective Java, Item 17: Design and document for inheritance or else prohibit it.
You also need to be explicit about methods you want to make overridable, also marked with open
:
open class Base {
open fun v() {}
fun nv() {}
}
The public
keyword acts as a visibility modifier that can be applied on classes, functions etc.
Note that public
is the default if nothing else is specified explicitly:
If you do not specify any visibility modifier,
public
is used by default, which means that your declarations will be visible everywhere
回答2:
class A { ... }
in Java is equal to open class A { ... }
in Kotlin.
final class B { ... }
in Java is equal to class B { ...}
in Kotlin.
It is not related with public
.
In Kotlin, everything without access modifiers is public
by default. You can explicitly say public
in the definition, but it is not necessary in Kotlin.
So,
public class A { ... }
and
class A { ... }
are the same in Kotlin.