Property and Backing Field

CA.kt #2

Transcript

1. Property and Backing Field @MoyuruAizawa
2. Ѫᖒ
   ๖ (Moyuru Aizawa) - Kotlin engineer at CyberAgent, Inc. - FRESH! lvla0805 MoyuruAizawa
3. Property?
4. class Person { val firstName: String val lastName: String … } Property
5. class Person { val firstName: String val lastName: String … } Property
6. Kotlin compiler generates Backing Fields and Accessors
7. public final class Person { @NotNull private final String firstName; @NotNull private final String lastName; … @NotNull public final String getFirstName() { return this.firstName; } @NotNull public final String getLastName() { return this.lastName; } } Backing Fields and Accessors
8. public final class Person { @NotNull private final String firstName; @NotNull private final String lastName; … @NotNull public final String getFirstName() { return this.firstName; } @NotNull public final String getLastName() { return this.lastName; } } Backing Fields
9. public final class Person { @NotNull private final String firstName; @NotNull private final String lastName; … @NotNull public final String getFirstName() { return this.firstName; } @NotNull public final String getLastName() { return this.lastName; } } Accessors
10. public final class Person { @NotNull private final String firstName; @NotNull private final String lastName; … @NotNull public final String getFirstName() { return this.firstName; } @NotNull public final String getLastName() { return this.lastName; } } Backing Fields
11. Declare Custom Accessors
12. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" … } Declare custom accessors
13. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" … } Declare custom accessors
14. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" … } Declare custom accessors
15. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" … } person.fullName Declare custom accessors
16. public final class Person { @NotNull private final String firstName; @NotNull private final String lastName; … @NotNull public final String getFirstName() { return this.firstName; } @NotNull public final String getLastName() { return this.lastName; } @NotNull public final String getFullName() { return this.firstName + " " + this.lastName; } } Declare custom accessors
17. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" var age: Int set(value) { require(value >= 0) field = value } … } Declare custom accessors
18. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" var age: Int set(value) { require(value >= 0) field = value } … } Declare custom accessors
19. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" var age: Int set(value) { require(value >= 0) field = value } … } Declare custom accessors
20. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" var age: Int set(value) { require(value >= 0) field = value } … } Declare custom accessors
21. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" var age: Int set(value) { require(value >= 0) age = value } … } Declare custom accessors Stack Overflow
22. class Person { val firstName: String val lastName: String val fullName get() = "$firstName $lastName" var age: Int set(value) { require(value >= 0) field = value } … } person.age = 26 Declare custom accessors
23. public final class Person { … private int age; … public final int getAge() { return this.age; } public final void setAge(int value) { required(value) this.age = value; } } Declare custom accessors
24. public final class Person { … private int age; … public final int getAge() { return this.age; } public final void setAge(int value) { required(value) this.age = value; } } Declare custom accessors
25. public final class Person { … private int age; … public final int getAge() { return this.age; } public final void setAge(int value) { required(value) this.age = value; } } Declare custom accessors
26. var <propertyName>[: <PropertyType>] [= <property_initializer>] [<getter>] [<setter>] Declare custom accessors
27. Properties without Backing Fields
28. class NoBackingField { val property get() = "property" } No Backing Fields
29. public final class NoBackingField { @NotNull public final String getProperty() { return "property"; } } No Backing Fields
30. Property without Backing Field ≒ Function
31. Interface can have Properties without Backing Fields
32. interface User { val id: Long val name: String } data class Follower(override val id: Long, override val name: String): User data class Me(override val id: Long, override val name: String, val email: String): User Interface can have Properties without Backing Fields
33. interface User { val id: Long val name: String } data class Follower(override val id: Long, override val name: String): User data class Me(override val id: Long, override val name: String, val email: String): User Interface can have Properties without Backing Fields
34. interface User { val id: Long val name: String } data class Follower(override val id: Long, override val name: String): User data class Me(override val id: Long, override val name: String, val email: String): User Interface can have Properties without Backing Fields
35. Extend a class with new Properties without Backing Fields
36. val View.isVisible get() = visibility == View.VISIBLE val Activity.applicationComponent get() = (application as CustomApplication).component Extend a class with new Properties without Backing Fields
37. val View.isVisible get() = visibility == View.VISIBLE val Activity.applicationComponent get() = (application as CustomApplication).component Extend a class with new Properties without Backing Fields
38. val View.isVisible get() = visibility == View.VISIBLE val Activity.applicationComponent get() = (application as CustomApplication).component Extend a class with new Properties without Backing Fields
39. ‣ Kotiln generates Backing Fields and Accessors ‣ You can declare custom Accessors ‣ Interface can have properties without Backing Fields ‣ You can extend a class with new Properties without Backing Fields
40. Thank you