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In Kotlin open is the same as not final in Java for classes and methods.
What does open give me in the following class for the field marked as open?
@MappedSuperclass abstract class BaseEntity() : Persistable<Long> { open var id: Long? = null } updated this is not duplicate of What is the difference between 'open' and 'public' in Kotlin?
I am interested in open keyword for properties
updated
open class can be inherited.open fun can be overriddenval property is final field in java
what about open property?
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It means Open classes and methods in Kotlin are equivalent to the opposite of final in Java, an open method is overridable and an open class is extendable in Kotlin. Note: your class is implicitly declared as open since it is abstract, hence you cannot create an instance of that class directly.
open modifier marks classes and methods as overridable. You need one per each method you want to be overridable. Now Button is marked as open, so it can be inherited. click() must be explicitly marked as open to be overridable.
The open keyword symbolizes open for extension. With the open keyword, any other class can inherit from this class. On the other hand, the public keyword is an access modifier. It is the default access modifier in Kotlin.
In certain computer programming languages, the Elvis operator ?: is a binary operator that returns its first operand if that operand is true , and otherwise evaluates and returns its second operand.
As you said, the open keyword allows you to override classes, when used in the class declaration. Accordingly, declaring a property as open, allows subclasses to override the property itself (e.g., redefine getter/setter). That keyword is required since in Kotlin everything is "final" by default, meaning that you can't override it (something similar to C#, if you have experience with that).
Note that your class is implicitly declared as open since it is abstract, hence you cannot create an instance of that class directly.
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