Effective Java to Effective Kotlin

Transcript

2. Integer x = 300; Integer y = 300; if(x == y) { println("Same Int"); } else { println("Diff Int”); }A
3. Integer x = 300; Integer y = 300; if(x == y) { println("Same Int"); } else { println("Diff Int”); }A prints Diff Int
4. Integer x = 300; Integer y = 300; if(x.equals(y)) { println("Same Int"); } else { println("Diff Int”); }A prints Diff Int
5. Integer x = 300; Integer y = 300; if(x.equals(y)) { println("Same Int"); } else { println("Diff Int”); }A prints Same Int
6. (ᵒ‒Д‒)ᵒኯᵲᴸᵲ
7. ᵣᴷᵣ ϊ( ʄ-ʄϊ)
10. Effective Java To Effective Kotlin Israel Ferrer Camacho @rallat
13. Item 3: Enforce the singleton property with a private constructor or an enum type
14. public enum EffectiveSingleton { INSTANCE }A
15. object EffectiveSingleton public enum EffectiveSingleton { INSTANCE }A
16. object EffectiveSingleton public final class EffectiveSingleton { public static final EffectiveSingleton INSTANCE; static { EffectiveSingleton var0 = new EffectiveSingleton(); INSTANCE = var0; } }
17. Item 2: Consider a builder when faced with many constructor parameters
18. public class Item { public final String id; public final String name; public final String description; }A
19. public class Item { public final String id; public final String name; public final String description; }A public static class Builder { private String name = ""; private String description = ""; public Item create(String id) { return new Item(id, description, name); }B public Builder name(String name) { this.name = name; return this; }C public Builder description(String description) { this.description = description; return this; }D }E
20. public static class Builder { private String name = ""; private String description = ""; public Item create(String id) { return new Item(id, description, name); }B public Builder name(String name) { this.name = name; return this; }C public Builder description(String description) { this.description = description; return this; }D }E
21. class Item( val id: String, val name: String = "", val description: String = "" ) public static class Builder { private String name = ""; private String description = ""; public Item create(String id) { return new Item(id, description, name); }B public Builder name(String name) { this.name = name; return this; }C public Builder description(String description) { this.description = description; return this; }D }E
22. class Item @JvmOverloads constructor( val id: String, val name: String = "", val description: String = "" ) public static class Builder { private String name = ""; private String description = ""; public Item create(String id) { return new Item(id, description, name); }B public Builder name(String name) { this.name = name; return this; }C public Builder description(String description) { this.description = description; return this; }D }E
23. class Item @JvmOverloads constructor( val id: String, val name: String = "", val description: String = "" )
24. class Item @JvmOverloads constructor( val id: String, val name: String = "", val description: String = "" ) Item("1")
25. class Item @JvmOverloads constructor( val id: String, val name: String = "", val description: String = "" ) Item("1") Item(name= "the name",id = "1")
26. Item 40: Consistently use the Override annotation
27. interface Header{ public void inflate(); } class AdHeader implements Header { public void inflate() { } }
28. interface Header{ public void inflate(); } class AdHeader implements Header { public void inflate() { } }
29. Item 17: Design for inheritance or else prohibit it
30. class NewMainActivity
31. class NewMainActivity
32. open class NewMainActivity class ClassicActivity: NewMainActivity()
33. Item 18: Favor composition over inheritance
34. interface Pump { void startMotor(); } class RotaryVane implements Pump interface Boiler { void heat(); } class DoubleBoiler implements Boiler
35. public class EspressoCoffeeMachine implements Boiler, Pump { private final DoubleBoiler boiler; private final RotaryVane pump; public EspressoCoffeeMachine(DoubleBoiler boiler, RotaryVane pump) { this.boiler = boiler; this.pump = pump; } @Override public void heat() { boiler.heat(); } @Override public void startMotor() { pump.startMotor(); } }
36. class EspressoCoffeeMachine : Boiler by DoubleBoiler, Pump by RotaryVane public class EspressoCoffeeMachine implements Boiler, Pump { private final DoubleBoiler boiler; private final RotaryVane pump; public EspressoCoffeeMachine(DoubleBoiler boiler, RotaryVane pump) { this.boiler = boiler; this.pump = pump; } @Override public void heat() { boiler.heat(); } @Override public void startMotor() { pump.startMotor(); } }
37. class EspressoCoffeeMachine : Boiler by DoubleBoiler, Pump by RotaryVane
38. 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; } } class EspressoCoffeeMachine : Boiler by DoubleBoiler, Pump by RotaryVane
39. Item 77: Don't ignore exceptions
40. public void close(Closeable c) { try { c.close(); } catch (IOException ignored) { } }
41. public int getCastValueToInt(String str) { int num = -1; try { num = Integer.parseInt(str); } catch (NumberFormatException ignored) {} return num; }
42. 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 }
43. Item 15 Minimize mutability
44. Item 8 Obey contract when overriding equals
45. Item 9: Always override hashCode when you override Equals
46. 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, " this.id = id; this.name = name; this.description = description;
47. 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) &&
48. 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() {
49. 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() { return (this.id.hashCode() * 31 + this.name.hashCode()) * 31 + this.description.hashCode(); }E }F
50. 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() { return (this.id.hashCode() * 31 + this.name.hashCode()) * 31 + this.description.hashCode(); }E }F
51. 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() { return (this.id.hashCode() * 31 + this.name.hashCode()) * 31 + this.description.hashCode(); }E }F data class Item(val id: String, val name: String, val description: String)
52. data class Item(val id: String, val name: String, val description: String) 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;
53. 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; }
54. data class Item(val id: String, val name: String, val description: String) 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;
55. 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; }
56. data class Item(val id: String, val name: String, val description: String) 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;
57. 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; } }
58. data class Item(val id: String, val name: String, val description: String) 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;
59. 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); }
60. data class Item(val id: String, val name: String, val description: String) 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;
61. 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 + ")"; }
62. data class Item(val id: String, val name: String, val description: String) 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;
63. 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; }
64. 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") }
65. data class Item(val id: String, val name: String, val description: String) : Parcelable 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; val(id, name, description) = fooItem() fun fooItem(): Item { return Item("id", "name", "description") }
66. data class Item(val id: String, val name: String, val description: String) : Parcelable 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;
67. @Parcelize data class Item(val id: String, val name: String, val description: String) : Parcelable 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;
68. 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()); } } @Parcelize data class Item(val id: String, val name: String, val description: String) : Parcelable
69. 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; @Parcelize data class Item(val id: String, val name: String, val description: String) : Parcelable
70. Item 43: Always return an empty collection instead of null
71. Handling Null references
72. public List<Item> getItem(String itemId)
73. @NotNull public List<Item> getItem(@NotNull String itemId)
74. @NotNull public List<Item> getItem(@NotNull String itemId)
75. @NotNull public List<Item> getItem(@NotNull String itemId)
76. @NotNull public List<Item> getItem(@NotNull String itemId) fun getItem(itemId: String) : List<Item>
77. fun getItem(itemId: String) : List<Item>
78. fun getItem(itemId: String) : List<Item> @NotNull public final List getItem(@NotNull String itemId)
79. fun getItem(itemId: String) : List<Item>
80. fun getItem(itemId: String) : List<Item>
81. fun getItem(itemId: String) : List<Item>
82. fun getItem(itemId: String) : List<Item>
83. fun getItem(itemId: String) : List<Item>
84. Chapter 6: Enums and annotations
86. Sealed classes
87. sealed class RemoteData
88. sealed class RemoteData { class NotInitialized : RemoteData() }A
89. sealed class RemoteData { object NotInitialized : RemoteData() }A
90. sealed class RemoteData { object NotInitialized : RemoteData() class Loading : RemoteData() }A
91. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() }A
92. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() class Success : RemoteData() }A
93. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() class Success : RemoteData() class Failure : RemoteData() }A
94. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() class Success(result: Response) : RemoteData() class Failure : RemoteData() }A
95. sealed class RemoteData { object NotInitialized : RemoteData() data class Loading(val progress: Progress) : RemoteData() class Success(result: Response) : RemoteData() class Failure(exception: Exception) : RemoteData() }A
96. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request }A
97. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request is RemoteData.Loading -> { viewModel.loading(request.progress) }B }A
98. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request is RemoteData.Loading -> { viewModel.loading(request.progress) }B is RemoteData.Success -> { viewModel.transform(request.result) }C }A
99. fun newState(request: RemoteData) = when (request) { RemoteData.NotInitialized -> request is RemoteData.Loading -> { viewModel.loading(request.progress) }B is RemoteData.Success -> { viewModel.transform(request.result) }C is RemoteData.Failure -> { viewModel.showError(request.exception) }D }A
101. Generics
102. Item 27: Favor generic methods
103. Reified
104. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java))
105. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java))
106. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java))
107. inline fun <reified T> Context.start() = startActivity(Intent(this, T::class.java)) start<PurchaseActivity>()
108. Item 28: Prefer lists to arrays
109. Java arrays are covariant
110. public final class Integer extends Number
111. Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L; public final class Integer extends Number
112. Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L; java.lang.ArrayStoreException: Long cannot be stored in an array of type Integer[] public final class Integer extends Number
113. Java List with generics are invariant
115. List enforces type safety at compile time.
116. Arrays in Kotlin are invariant and allow generics
117. Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L; java.lang.ArrayStoreException: Long cannot be stored in an array of type Integer[]
118. Integer[] integers = new Integer[1]; Number[] numbers = integers; numbers[0] = 1L; java.lang.ArrayStoreException: Long cannot be stored in an array of type Integer[]
119. Item 31: Use bounded wildcards to increase API flexibility
120. class Stack<E> { public void pushAll(Iterable<E> src) { for (E e : src) push(e); }A }B
121. class Stack<E> { public void pushAll(Iterable<E> src) { for (E e : src) push(e); }A }B
122. ?
124. <? extends T>
125. <? extends T> <? super T>
126. PECS stands for producer- extends, consumer-super.
127. class Stack<E> { public void pushAll(Iterable<E> src) { for (E e : src) push(e); } }
128. class Stack<E> { public void pushAll(Iterable<? extends E> src) { for (E e : src) push(e); } }
129. class Stack<E> { public void pushAll(Iterable<? extends E> src) { for (E e : src) push(e); }A }B Stack<Number> stack = new Stack<>(); List<Integer> integers = new ArrayList<>(); stack.pushAll(integers);
130. 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()); } }
131. Use-site variance
132. 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()); } }
133. 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()) } }
134. Consumer in, Producer out!
135. Declaration-site variance
136. interface Source<out T> { fun next(): T } interface Consumer<in T> { fun consume(t: T) }
137. interface Source<out T> { fun next(): T } interface Consumer<in T> { fun consume(t: T) }
138. Generics
139. Kotlin solves many of the Java language issues
140. Kotlin brings fluency
141. itemArray .asSequence() .filter { specialItem.contains(it.id) } .map { it.price } .average()
143. Less Boilerplate More Features
145. IntelliJ
146. IntelliJ Lambda expressions
147. IntelliJ Lambda expressions Smart casts
148. IntelliJ Lambda expressions Smart casts String templates
149. IntelliJ Lambda expressions Smart casts String templates Type inference
150. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias
151. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions
152. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading
153. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects
154. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects Coroutines
155. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects Coroutines Contracts
156. IntelliJ Lambda expressions Smart casts String templates Type inference Typealias Range expressions Operator overloading Companion objects Coroutines Contracts Inline classes
157. Why are we still using Java?
158. Effective Java To Effective Kotlin Israel Ferrer Camacho @rallat