How 'Effective Java' influenced Kotlin - Droidcon Vienna 2018

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1. @lukleDev
5. public class NutritionFacts { private final int servingSize; // required private final int servings; // required private final int calories; optional private final int carbohydrates; // optional private final int protein; // optional private final int fat; // optional }
6. public class NutritionFacts { private final int servingSize; // required private final int servings; // required private final int calories; optional private final int carbohydrates; // optional private final int protein; // optional private final int fat; // optional }
7. public class NutritionFacts { private final int servingSize; // required private final int servings; // required private final int calories; optional private final int carbohydrates; // optional private final int protein; // optional private final int fat; // optional }
8. public class NutritionFacts { private final int servingSize; // required private final int servings; // required private final int calories; optional private final int carbohydrates; // optional private final int protein; // optional private final int fat; // optional } • • •
9. • • • • NutritionFacts pie = new NutritionFacts.Builder(240, 8) .calories(100) .carbohydrates(10) .protein(4) .build();
12. class KotlinNutritionFacts( 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)
13. class KotlinNutritionFacts( 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)
14. class KotlinNutritionFacts( 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)
15. class KotlinNutritionFacts( 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)
16. class KotlinNutritionFacts( 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)
17. val pie = KotlinNutritionFacts(240, 8)
18. val pie = KotlinNutritionFacts(240, 8) val pie = KotlinNutritionFacts(240, 8, calories = 100, fat = 2)
19. val pie = KotlinNutritionFacts(240, 8) val pie = KotlinNutritionFacts(240, 8, calories = 100, fat = 2) val pie = KotlinNutritionFacts( servingSize = 240, servings = 8, calories = 100, fat = 2 )
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21. private val isVegan: Boolean = false, private val containsGluten: Boolean = false
22. private val isVegan: Boolean = false, private val containsGluten: Boolean = false val pie = nutritionFacts(servingSize = 240, servings = 8) { additionalInformation { +isVegan +containsGluten } }
24. public class Elvis { private static final Elvis INSTANCE = new Elvis(); private Elvis() { } public static Elvis getInstance() { return INSTANCE; } public void leaveTheBuilding() { System.out.println("Whoa baby, I'm outta here!"); } }
25. public class Elvis { private static final Elvis INSTANCE = new Elvis(); private Elvis() { } public static Elvis getInstance() { return INSTANCE; } public void leaveTheBuilding() { System.out.println("Whoa baby, I'm outta here!"); } }
26. public class Elvis { private static final Elvis INSTANCE = new Elvis(); private Elvis() { } public static Elvis getInstance() { return INSTANCE; } public void leaveTheBuilding() { System.out.println("Whoa baby, I'm outta here!"); } }
27. public class Elvis { private static final Elvis INSTANCE = new Elvis(); private Elvis() { } public static Elvis getInstance() { return INSTANCE; } public void leaveTheBuilding() { System.out.println("Whoa baby, I'm outta here!"); } }
28. public class Elvis { private static final Elvis INSTANCE = new Elvis(); private Elvis() { } public static Elvis getInstance() { return INSTANCE; } public void leaveTheBuilding() { System.out.println("Whoa baby, I'm outta here!"); } }
29. object KotlinElvis { fun leaveTheBuilding(){ println("Whoa baby, I'm outta here!") } }
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32. public class TextUtils { // Suppresses default constructor, ensuring non-instantiability. private TextUtils() {} ... public static boolean isEmpty(@Nullable CharSequence str) { return str == null || str.length() == 0; } ... }
33. public class TextUtils { // Suppresses default constructor, ensuring non-instantiability. private TextUtils() {} ... public static boolean isEmpty(@Nullable CharSequence str) { return str == null || str.length() == 0; } ... }
34. class TextUtils private constructor(){ ... }
35. // File: TextUtils.kt fun isEmpty(CharSequence? str): Boolean { return str == null || str.length == 0 }
36. // File: TextUtils.kt fun isEmpty(CharSequence? str): Boolean { return str == null || str.length == 0 } // Another file fun main(args: Array<String>) { val name: String? = ".." isEmpty(name) }
37. // File: TextUtils.kt fun String?.isEmpty(): Boolean { return this == null || this.length == 0 }
38. // File: TextUtils.kt fun String?.isEmpty(): Boolean { return this == null || this.length == 0 } // Another file fun main(args: Array<String>) { val name: String? = "..." name.isEmpty() }
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41. public class Sum { // Hideously slow program! public static void main(String[] args) { Long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } }
42. public class Sum { // Hideously slow program! public static void main(String[] args) { Long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } }
43. public class Sum { // Hideously slow program! public static void main(String[] args) { Long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } }
44. public class Sum { // Hideously slow program! public static void main(String[] args) { Long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } }
45. public class Sum { // Hideously slow program! public static void main(String[] args) { Long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } }
46. public class Sum { // Hideously slow program! public static void main(String[] args) { Long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } }
47. public class Sum { // Hideously slow program! public static void main(String[] args) { // primitive long instead of the Long reference type long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } }
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51. • • ◦ ◦ ◦ // So we will still have performance issues if we use Long? var sum: Long? = 0L
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55. • equals() • hashCode() • toString() • when how
57. data class Person(val name: String, val age: Int)
58. public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof Person) { Person var2 = (Person)var1; if (Intrinsics.areEqual(this.name, var2.name) && this.age == var2.age) { return true; } } return false; } else { return true; } }
59. public int hashCode() { return (this.name != null ? this.name.hashCode() : 0) * 31 + this.age; }
60. public int hashCode() { return (this.name != null ? this.name.hashCode() : 0) * 31 + this.age; } public String toString() { return "Person(name=" + this.name + ", age=" + this.age + ")"; }
61. • hashCode(), equals() toString() • • • + =
63. public class JavaPerson { // don't use public fields in public classes! public String name; public Integer age; } • •
64. public class JavaPerson { private String name; private Integer age; }
65. public class JavaPerson { private String name; private Integer age; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } }
67. class KotlinPerson { var name: String? = null var age: Int? = null }
68. class KotlinPerson { var name: String? = null var age: Int? = null } kotlinPerson.name
69. class KotlinPerson { var name: String? = null var age: Int? = null } kotlinPerson.name kotlinPerson.age = 18
70. class KotlinPerson { var name: String? = null var age: Int? = null set(value) { if (value in 0..120){ field = value } else{ throw IllegalArgumentException() } } }
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73. • • final • • open
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