Effective Java In Kotlin World

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

6. None

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

31. None
32. None

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() {
46. None

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)

61. None
62. None

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

76. None

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

104. None

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?