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Property + Getter
ू·ΕKotlin͖ʂKotlinѪձ vol2
scache( @scal_ch )
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About me
• scache ( @scal_ch )
• Android/Kotlin
• AbemaTV
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val + getter vs fun
val isEmpty get() = size == 0
or
fun isEmpty() = size == 0
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Properties
• var/val
• var/val + custom getter
• Property Delegation(e.g. lazy)
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var (not null)
class Var(var varHoge: String = “var”)
Var().let {
it.varHoge.toList()
}
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val(not null)
class Val(val valHoge: String = "not null")
Val().let {
it.valHoge.toList()
}
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var
class Var(var varHoge: String? = “var”)
Var().let {
it.varHoge ?: return@let
it.varHoge toList()
}
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var
class Var(var varHoge: String? = “var”)
Var().let {
it.varHoge ?: return@let
it.varHoge?.toList()
}
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val
class Val(val valHoge: String? = "not null")
Val().let {
it.valHoge ?: return@let
it.valHoge toList()
}
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val
class Val(val valHoge: String? = "not null")
Val().let {
it.valHoge ?: return@let
it.valHoge.toList()
}
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var + custom getter
class VarGetter {
val rand = Random()
var varGetter: String? = null
get() = "random: ${rand.nextInt()}"
}
VarGetter().let {
it.varGetter ?: return@let
it.varGetter toList()
}
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var + custom getter
class VarGetter {
val rand = Random()
var varGetter: String? = null
get() = "random: ${rand.nextInt()}"
}
VarGetter().let {
it.varGetter ?: return@let
it.varGetter?.toList()
}
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val + custom getter
class ValGetter(
var hoge: String? = "not null"
) {
val valNullable: String?
get() = hoge
}
ValGetter().let {
it.valNullable ?: return@let
it.valNullable toList()
}
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val + custom getter
class ValGetter(
var hoge: String? = "not null"
) {
val valNullable: String?
get() = hoge
}
ValGetter().let {
it.valNullable ?: return@let
it.valNullable?.toList()
}
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Declaring Properties
These can be declared as mutable, using the var keyword
or read-only using the val keyword.
https://kotlinlang.org/docs/reference/properties.html#declaring-properties
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Declaring Properties
These can be declared as mutable, using the var keyword
or read-only using the val keyword.
https://kotlinlang.org/docs/reference/properties.html#declaring-properties
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val + lazy
class LazyVal {
val hoge: String? by lazy { "not null" }
}
LazyVal().let {
it.hoge ?: return@let
it.hoge toList()
}
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val + lazy
class LazyVal {
val hoge: String? by lazy { "not null" }
}
LazyVal().let {
it.hoge ?: return@let
it.hoge?.toList()
}
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val + getter vs fun
val isEmpty get() = size == 0
or
fun isEmpty() = size == 0
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Kotlin Πϯ ΞΫγϣϯʹΑΔͱ
Ҿͷͳ͍ؔͱΧελϜGetterΛ࣋ͭϓϩύςΟՄಡੑ
ʹͷΈҧ͍͕͋Δ
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Kotlin Πϯ ΞΫγϣϯʹΑΔͱ
Ҿͷͳ͍ؔͱΧελϜGetterΛ࣋ͭϓϩύςΟՄಡੑ
ʹͷΈҧ͍͕͋Δ
hoge.isEmpty
or
hoge.isEmpty()
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Kotlin Πϯ ΞΫγϣϯʹΑΔͱ
Ҿͷͳ͍ؔͱΧελϜGetterΛ࣋ͭϓϩύςΟՄಡੑ
ʹͷΈҧ͍͕͋Δ
ΫϥεͷಛΛදݱ͍ͨ͠߹ʹϓϩύςΟʹ͢Δ
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kotlin-stdlib
public val List.lastIndex: Int
get() = this.size - 1
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Functions vs Properties
Prefer a property one a function when the underlying
algorithm
• does not throw
• is cheap to calculate
• returns the same result over innovations if the object state
hasn’t changed
https://kotlinlang.org/docs/reference/coding-conventions.html#functions-vs-properties
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·ͱΊ
ݸਓతͳҙݟ
• valมͷ࣮Λݟͳ͍ͱ͕ෆม͔Ͳ͏͔ෆ໌
• Functions vs Properties ͷϧʔϧʹै͏
• ໎ͬͨΒfun
• ผͷҙݟฉ͖͍ͨͷͰ࠙ձͰ͓ئ͍͠·͢ʂ
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No content
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͓·͚ J2K
Branch A
1. javaϑΝΠϧΛίϐʔͯ͠ktϑΝΠϧΛ࡞
2. ktϑΝΠϧΛमਖ਼
3. javaϑΝΠϧΛফͯ͠ίϛοτ
Branch B
1. javaϑΝΠϧΛktϑΝΠϧʹϦωʔϜͯ͠ίϛοτ
2. ktϑΝΠϧͷ༰ΛBranchA͔Β͖࣋ͬͯͯίϛοτ