Effective Java In Kotlin World

Effective Java In Kotlin World presentation slides.

Transcript

1. Integer x = 300; Integer y = 300; if(x == y) { println("Same Int"); } else { println("Diff Int”); } Video Link: https://www.youtube.com/playlist?list=PLT2xIm2X7W7jqdoYI5EXpYkuOPkWngOP3
2. Integer x = 300; Integer y = 300; if(x == y) { println("Same Int"); } else { println("Diff Int”); } prints Diff Int
3. Integer x = 300; Integer y = 300; if(x.equals(y) { println("Same Int"); } else { println("Diff Int”); } prints Diff Int
4. Integer x = 300; Integer y = 300; if(x.equals(y) { println("Same Int"); } else { println("Diff Int”); } prints Same Int
5. Effective Java In Kotlin World ینیسح دواد دیس https://github.com/DHosseiny @Hosseinydavid
7. Item 3: Enforce the singleton property with a private constructor or an enum type
8. public class Elvis { private static final Elvis INSTANCE = new Elvis(); private Elvis() { } public static Elvis getInstance() { return INSTANCE; } public void leaveTheBuilding() { ... } }
9. object Elvis
10. object Elvis
11. object Elvis public final class Elvis { public static final Elvis INSTANCE; static { Elvis var0 = new Elvis(); INSTANCE = var0; } }
12. Item 2: Consider a builder when faced with many constructor parameters
13. public class NutritionFacts { private final int servingSize; // required private final int servings; // required private final int calories; // optional private final int fat; // optional private final int sodium; // optional private final int carbohydrate; // optional }
14. public static class Builder { // Required parameters private final int servingSize; private final int servings; // Optional parameters - initialized to default values private int calories = 0; private int fat = 0; private int carbohydrate = 0; private int sodium = 0; public Builder(int servingSize, int servings) { this.servingSize = servingSize; this.servings = servings; } public Builder calories(int val) { calories = val; return this; } public Builder fat(int val) { fat = val; return this; } public Builder carbohydrate(int val) { carbohydrate = val; return this; } public Builder sodium(int val) { sodium = val; return this; } public NutritionFacts build() { return new NutritionFacts(this); } } public class NutritionFacts { private final int servingSize; private final int servings; private final int calories; private final int fat; private final int sodium; private final int carbohydrate;
15. public static class Builder { // Required parameters private final int servingSize; private final int servings; // Optional parameters - initialized to default values private int calories = 0; private int fat = 0; private int carbohydrate = 0; private int sodium = 0; public Builder(int servingSize, int servings) { this.servingSize = servingSize; this.servings = servings; } public Builder calories(int val) { calories = val; return this; } public Builder fat(int val) { fat = val; return this; } public Builder carbohydrate(int val) { carbohydrate = val; return this; } public Builder sodium(int val) { sodium = val; return this; } public NutritionFacts build() { return new NutritionFacts(this); } } public class NutritionFacts { private final int servingSize; private final int servings; private final int calories; private final int fat; private final int sodium; private final int carbohydrate; private NutritionFacts(Builder builder) { servingSize = builder.servingSize; servings = builder.servings; calories = builder.calories; fat = builder.fat; sodium = builder.sodium; carbohydrate = builder.carbohydrate; } }
16. NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8) .calories(100) .sodium(35) .carbohydrate(27) .build();
17. class NutritionFacts private val servingSize: Int, private val servings: Int, private val calories: Int = 0, private val fat: Int = 0, private val sodium: Int = 0, private val carbohydrates: Int = 0) (
18. class NutritionFacts private val servingSize: Int, private val servings: Int, private val calories: Int = 0, private val fat: Int = 0, private val sodium: Int = 0, private val carbohydrates: Int = 0) // default value // default value // default value // default value (
19. class NutritionFacts private val servingSize: Int, private val servings: Int, private val calories: Int = 0, private val fat: Int = 0, private val sodium: Int = 0, private val carbohydrates: Int = 0) // no default value // no default value // default value // default value // default value // default value (
20. class NutritionFacts @JvmOverloads constructor( private val servingSize: Int, private val servings: Int, private val calories: Int = 0, private val fat: Int = 0, private val sodium: Int = 0, private val carbohydrates: Int = 0) // no default value // no default value // default value // default value // default value // default value
21. val cocaCola = NutritionFacts( servingSize = 240, servings = 8)
22. val cocaCola = NutritionFacts( servingSize = 240, servings = 8, fat = 240, calories = 100, carbohydrates = 27 ) val cocaCola = NutritionFacts( servingSize = 240, servings = 8)
23. val cocaCola = NutritionFacts( servingSize = 240, servings = 8, fat = 240, calories = 100, carbohydrates = 27 ) val cocaCola = NutritionFacts( servingSize = 240, servings = 8)
24. Item 19: Design and document for inheritance or else prohibit it
25. class NewMainActivity
26. class NewMainActivity
27. class NewMainActivity
28. class NewMainActivity open
29. class NewMainActivity open
30. Item 18: Favor composition over inheritance
33. class EspressoCoffeeMachine : Boiler by DoubleBoiler, Pump by RotaryVane
34. class EspressoCoffeeMachine : Boiler by DoubleBoiler, Pump by RotaryVane
35. class EspressoCoffeeMachine : Boiler by DoubleBoiler, Pump by RotaryVane public final class EspressoCoffeeMachine implements Boiler, Pump { private final DoubleBoiler $$delegate_0; private final RotaryVane $$delegate_1; public EspressoCoffeeMachine() { this.$$delegate_0 = DoubleBoiler.INSTANCE; this.$$delegate_1 = RotaryVane.INSTANCE; } }
36. Item 77: Don't ignore exceptions
37. public void close(Closeable c) { try { c.close(); } catch (IOException ignored) { } }
38. public int getCastValueToInt(String str) { int num = -1; try { num = Integer.parseInt(str); } catch (NumberFormatException ignored) {} return num; }
39. public int getCastValueToInt(String str) { int num = -1; try { num = Integer.parseInt(str); } catch (NumberFormatException ignored) {} return num; } fun getCastValueToInt(string: String) = try { Integer.parseInt(string); } catch (e: NumberFormatException) { -1 }
40. Item 17: Minimize mutability
41. Item 10: Obey contract when overriding equals
42. Item 9: Always override hashCode when you override Equals
43. Item 12: Always Override toString
44. public class ItemJava { @NotNull public final String id; @NotNull public final String name; @NotNull public final String description; public ItemJava(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); this.id = id; this.name = name; this.description = description; }A }
45. public class ItemJava { @NotNull public final String id; @NotNull public final String name; @NotNull public final String description; public ItemJava(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); this.id = id; this.name = name; this.description = description; }A public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof ItemJava) { ItemJava var2 = (ItemJava) var1; return Intrinsics.areEqual(this.id, var2.id) && Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.description, var2.description); }B return false; } else { return true; }C }D } public int hashCode() {
47. data class Item(val id: String, val name: String, val description: String)
48. data class Item(val id: String, val name: String, val description: String)
49. public final class Item { @NotNull private final String id; @NotNull private final String name; @NotNull private final String description; @NotNull public final String getId() { return this.id; } @NotNull public final String getName() { return this.name; } @NotNull public final String getDescription() { return this.description; } public Item(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); super(); this.id = id; this.name = name; this.description = description; } @NotNull public final String component1() { return this.id; } @NotNull public final String component2() { return this.name; } @NotNull public final String component3() { return this.description; } @NotNull public final Item copy(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); return new Item(id, name, description); } // $FF: synthetic method // $FF: bridge method @NotNull public static Item copy$default(Item var0, String var1, String var2, String var3, int var4, Object var5) { if ((var4 & 1) != 0) { var1 = var0.id; } if ((var4 & 2) != 0) { var2 = var0.name; } if ((var4 & 4) != 0) { var3 = var0.description; } return var0.copy(var1, var2, var3); } public String toString() { return "Item(id=" + this.id + ", name=" + this.name + ", description=" + this.description + ")"; } public int hashCode() { return ((this.id != null ? this.id.hashCode() : 0) * 31 + (this.name != null ? this.name.hashCode() : 0)) * 31 + (this.description != null ? this.description.hashCode() : 0); } public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof Item) { Item var2 = (Item)var1; if (Intrinsics.areEqual(this.id, var2.id) && Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.description, var2.description)) { return true; } } return false; } else { return true; data class Item(val id: String, val name: String, val description: String)
50. data class Item(val id: String, val name: String, val description: String) public Item(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); super(); this.id = id; this.name = name; this.description = description; }
51. data class Item(val id: String, val name: String, val description: String) @NotNull public final String getId() { return this.id; } @NotNull public final String getName() { return this.name; } @NotNull public final String getDescription() { return this.description; }
52. data class Item(val id: String, val name: String, val description: String) public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof Item) { Item var2 = (Item)var1; if (Intrinsics.areEqual(this.id, var2.id) && Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.description, var2.description)) { return true; } } return false; } else { return true; } }
53. data class Item(val id: String, val name: String, val description: String) public int hashCode() { return ((this.id != null ? this.id.hashCode() : 0) * 31 + (this.name != null ? this.name.hashCode() : 0)) * 31 + (this.description != null ? this.description.hashCode() : 0); }
54. data class Item(val id: String, val name: String, val description: String) @NotNull public final Item copy(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); return new Item(id, name, description); } public String toString() { return "Item(id=" + this.id + ", name=" + this.name + ", description=" + this.description + ")"; }
55. data class Item(val id: String, val name: String, val description: String) @NotNull public final String component1() { return this.id; } @NotNull public final String component2() { return this.name; } @NotNull public final String component3() { return this.description; }
56. data class Item(val id: String, val name: String, val description: String) @NotNull public final String component1() { return this.id; } @NotNull public final String component2() { return this.name; } @NotNull public final String component3() { return this.description; } val(id, name, description) = fooItem() fun fooItem(): Item { return Item("id", "name", "description") }
57. data class Item(val id: String, val name: String, val description: String) @NotNull public final String component1() { return this.id; } @NotNull public final String component2() { return this.name; } @NotNull public final String component3() { return this.description; } @Parcelize
58. data class Item(val id: String, val name: String, val description: String) @Parcelize public void writeToParcel(@NotNull Parcel parcel, int flags) { Intrinsics.checkParameterIsNotNull(parcel, "parcel"); parcel.writeString(this.id); parcel.writeString(this.name); parcel.writeString(this.description); } @Metadata( mv = {1, 1, 13}, bv = {1, 0, 3}, k = 3 ) public static class Creator implements Parcelable.Creator { @NotNull public final Object[] newArray(int size) { return new Item[size]; } @NotNull public final Object createFromParcel(@NotNull Parcel in) { Intrinsics.checkParameterIsNotNull(in, "in"); return new Item(in.readString(), in.readString(), in.readString()); }
59. data class Item(val id: String, val name: String, val description: String) @Parcelize public final class Item { @NotNull private final String id; @NotNull private final String name; @NotNull private final String description; @NotNull public final String getId() { return this.id; } @NotNull public final String getName() { return this.name; } @NotNull public final String getDescription() { return this.description; } public Item(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); super(); this.id = id; this.name = name; this.description = description; } @NotNull public final String component1() { return this.id; } @NotNull public final String component2() { return this.name; } @NotNull public final String component3() { return this.description; } @NotNull public final Item copy(@NotNull String id, @NotNull String name, @NotNull String description) { Intrinsics.checkParameterIsNotNull(id, "id"); Intrinsics.checkParameterIsNotNull(name, "name"); Intrinsics.checkParameterIsNotNull(description, "description"); return new Item(id, name, description); } // $FF: synthetic method // $FF: bridge method @NotNull public static Item copy$default(Item var0, String var1, String var2, String var3, int var4, Object var5) { if ((var4 & 1) != 0) { var1 = var0.id; } if ((var4 & 2) != 0) { var2 = var0.name; } if ((var4 & 4) != 0) { var3 = var0.description; } return var0.copy(var1, var2, var3); } public String toString() { return "Item(id=" + this.id + ", name=" + this.name + ", description=" + this.description + ")"; } public int hashCode() { return ((this.id != null ? this.id.hashCode() : 0) * 31 + (this.name != null ? this.name.hashCode() : 0)) * 31 + (this.description != null ? this.description.hashCode() : 0); } public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof Item) { Item var2 = (Item)var1; if (Intrinsics.areEqual(this.id, var2.id) && Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.description, var2.description)) { return true; } } return false; } else { return true;
60. public List<Item> getItem(String itemId) getItem(null)
63. Item 54: Return empty collections or arrays, not nulls
64. Handling Null references
65. public List<Item> getItem(String itemId)
66. @NotNull public List<Item> getItem(@NotNull String itemId)
67. @NotNull public List<Item> getItem(@NotNull String itemId)
68. @NotNull public List<Item> getItem(@NotNull String itemId)
69. @NotNull public List<Item> getItem(@NotNull String itemId) fun getItem(itemId: String) : List<Item>
70. fun getItem(itemId: String) : List<Item> @NotNull public final List getItem(@NotNull String itemId)
71. fun getItem(itemId: String) : List<Item>
72. fun getItem(itemId: String) : List<Item>
73. fun getItem(itemId: String) : List<Item>
74. fun getItem(itemId: String) : List<Item>
75. Chapter 6: Enums and annotations
77. Sealed classes
78. sealed class RemoteData
79. sealed class RemoteData { class NotInitialized : RemoteData() }
80. sealed class RemoteData { object NotInitialized : RemoteData() }
81. sealed class RemoteData { object NotInitialized : RemoteData() class Loading } : RemoteData()
82. sealed class RemoteData { object NotInitialized : RemoteData() class Loading } (val progress: Progress) : RemoteData()
83. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() class Success : RemoteData() }
84. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() } class Success: RemoteData() class Failure: RemoteData()
85. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() } class Success(result: Response): RemoteData() class Failure: RemoteData()
86. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() } class Success(result: Response): RemoteData() class Failure(exception: Exception): RemoteData()
87. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request }
88. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request is RemoteData.Loading -> { viewModel.loading(request.progress) } }
89. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request is RemoteData.Loading -> { viewModel.loading(request.progress) } is RemoteData.Success -> { viewModel.transform(request.result) } }
90. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request is RemoteData.Loading -> { viewModel.loading(request.progress) } is RemoteData.Success -> { viewModel.transform(request.result) } is RemoteData.Failure -> { viewModel.showError(request.exception) } }
91. Generics
92. Item 27: Favor generic methods
93. Reified
94. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java))
95. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java))
96. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java))
97. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java)) start<PurchaseActivity>()
98. Item 28: Prefer lists to arrays
99. Java arrays are covariant
100. public final class Integer extends Number
101. public final class Integer extends Number Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L;
102. public final class Integer extends Number Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L; java.lang.ArrayStoreException: Long cannot be stored in an array of type Integer[]
103. Java List with generics are invariant and erased
105. List enforces type safety at compile time
106. Arrays in Kotlin are invariant and allow generics
107. Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L; java.lang.ArrayStoreException: Long cannot be stored in an array of type Integer[]
108. Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L; java.lang.ArrayStoreException: Long cannot be stored in an array of type Integer[]
109. Item 31: Use bounded wildcards to increase API flexibility
110. class Stack<E> { public void pushAll(Iterable<E> src) { for (E e : src) push(e); } }
111. class Stack<E> { public void pushAll(Iterable<E> src) { for (E e : src) push(e); } }
112. ?
113. <? extends T> <? super T>
114. PECS stands for producer- extends, consumer-super.
115. class Stack<E> { public void pushAll(Iterable<E> src) { for (E e : src) push(e); } }
116. class Stack<E> { public void pushAll(Iterable<? extends E> src) { for (E e : src) push(e); } }
117. Stack<Number> stack = new Stack<>(); List<Integer> integers = new ArrayList<>(); stack.pushAll(integers); class Stack<E> { public void pushAll(Iterable<? extends E> src) { for (E e : src) push(e); } }
118. class Stack<E> { public void pushAll(Iterable<? extends E> src) { for (E e : src) push(e); } public void popAll(Collection<? super E> dst) { while (!isEmpty()) dst.add(pop()); } }
119. Use-site variance
120. class Stack<E> { public void pushAll(Iterable<? extends E> src) { for (E e : src) push(e); } public void popAll(Collection<? super E> dst) { while (!isEmpty()) dst.add(pop()); } } class Stack<E> { fun pushAll(src: Iterable<out E>) { for (e in src) push(e) } fun popAll(dst: MutableList<in E>) { while (!isEmpty()) dst.add(pop()) } }
121. Consumer in, Producer out!
122. Declaration-site variance
123. interface Source<out T> { fun next(): T } interface Consumer<in T> { fun consume(t: T) }
124. <out T> T er<in T> { { t: T) interface Source fun next(): } interface Consum fun consume( }
125. Generics
126. Kotlin solves many of the Java language issues
127. + =
128. Less Boilerplate More Features
129. IntelliJ
130. IntelliJ Lambda expressions
131. IntelliJ Lambda expressions Smart casts
132. IntelliJ Lambda expressions Smart casts String templates
133. IntelliJ Lambda expressions Smart casts String templates Type inference
134. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias
135. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions
136. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading
137. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects
138. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects Coroutines
139. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects Coroutines Contracts
140. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects Coroutines Contracts Inline classes
141. Why are we still using Java?
142. @Hosseinydavid + = Questions?