This document provides an overview of Kotlin basics including: - Basic data types like Int, String, Boolean - Collections like List, Set, Map - Variables, functions, control flow - Classes, properties, constructors - Inheritance, interfaces - Additional features like lambdas, extensions, coroutines It aims to introduce fundamental Kotlin concepts and syntax in a concise manner.

1. Sprint Part 2
otlin Basics

2. Kirill Rozov
Senior Android Developer
kiryl.rozau
kiryl.rozau@apalon.com

3. Basic Types

4. Base types
• Byte
• Short
• Int
• Long
• Float
• Double
• Char
• Boolean

5. Arrays
byte[] ByteArray
short[] ShortArray
int[] IntArray
long[] LongArray
float[] FloatArray
double[] DoubleArray
boolean[] BooleanArray
char[] CharArray
String Array<String>

6. String Templates
"the element at $index is $value"
"the element at $index hash code is ${value.hashCode()}”

7. Variables

8. Variables
var variable: String = "variable"

9. Variables
var variable: String = "variable"

10. Variables
var variable: String = "variable"

11. Variables
var variable: String = "variable"

12. Variables
var variable: String = "variable"
variable = “update”
variable = null // Compile error

13. Variables
variable = “update”
variable = null // Compile error
var variable: String = "variable"

14. Variables
var variable: String = "variable"
variable = null // Compile error

15. Variables
var variable: String? = "variable"
variable = null

16. Variables
var variable: String = "variable"

17. Variables
val variable: String = "variable"

18. Variables
val variable: String = "variable"
variable = “update” // Compile error

19. Variables
val variable: String = "variable"

20. Variables
val variable: String = "variable"

21. val variable = "variable"
Explicit variable type

22. val list = ArrayList<String>()
Explicit variable type

23. val list: ArrayList<String> = ArrayList<String>()
Explicit variable type

24. val list: ArrayList<String> = ArrayList<String>()
Explicit variable type

25. val list: ArrayList<String> = ArrayList()
Explicit variable type

26. val list: ArrayList<String> = ArrayList()
Explicit variable type

27. val list: List<String> = ArrayList()
Explicit variable type

28. Type Checks & Casts: ‘is’ & ’as’

29. ‘is’ & ’as’
if (obj is String) {
val string = obj as String
print(string.length)
}

30. ‘is’ & ’as’
if (obj is String) {
print(obj.length)
}

31. obj as String
print(obj.length)
‘is’ & ’as’

32. Safe Casts
val safeObject: String? = obj as? String

33. Null Safety

34. Null Safety
val keyValues: Map<String, String> = Collections.emptyMap()
val value = keyValues.get("Sample key")
value.substring(1) // Compile error

35. Null Safety
val value = keyValues.get("Sample key")
value.substring(1) // Compile error

36. Null Safety
val value: String? = keyValues.get("Sample key")
value.substring(1) // Compile error

37. Safe call
val value: String? = keyValues.get("Sample key")
value?.substring(1)

38. Safe call
val value = keyValues.get("Sample key")
value?.substring(1)

39. Safe call
val value = keyValues.get("Sample key")
value?.substring(1)
if (value == null) return

40. Safe call
val value = keyValues.get("Sample key")
value?.substring(1)
if (value == null) return

41. Smart Cast
val value = keyValues.get("Sample key")
value.substring(1)
if (value == null) return

42. Null Elvis Operator
val value: String? = keyValues.get("Sample key")
value?.substring(1) ?: "Default"

43. Operator !!
var value: String? = null
value!!.substring(1)

44. Operator !!
var value: String? = null
value!!.substring(1)

45. Control flow

46. If-else
if (condition) {
…
} else if (…) {
…
} else {
…
}

47. If-else
if (num > 0) {
return 1
} else if (num < 0) {
return -1
} else {
return 0
}

48. If-else
return if (num > 0) {
1
} else if (num < 0) {
-1
} else {
0
}

49. If-else
return if (num > 0) 1
else if (num < 0) -1
else 0

50. When
when (x) {
1 -> print("x == 1")
2 -> print("x == 2")
3 -> print("x == 3")
else -> print("Unknown")
}

51. When
when (x) {
1, 2, 3 -> print("x == $x”)
else -> print("Unknown")
}

52. When
when (x) {
parseInt(s) -> print("s encodes x")
else -> print("s does not encode x")
}

53. When
when {
x in 1..10 -> print("x is in the range")
x in validNumbers -> print("x is valid")
x !in 10..20 -> print("x is outside the range")
else -> print("none of the above")
}

54. for
for (item in collection) print(item)
for (item: String in collection) {
print(item)
}
for (i in collection.indices) {
println(collection[i])
}
for ((index, value) in collection.withIndex()) {
println("the element at $index is $value")
}

55. Functions

56. Functions
fun sample(arg1: Boolean): String {
…
}

57. Functions
fun sample(arg1: Boolean): String {
…
}

58. Functions
fun sample(arg1: Boolean): String {
…
}

59. Functions
fun sample(arg1: Boolean): String {
…
}

60. Functions
fun sample(arg1: Boolean): String {
…
}

61. Functions
fun scaleX(scale: Float, centerX: Int): Unit {
…
}

62. Functions
fun scaleX(scale: Float, centerX: Int): Unit {
…
}

63. Functions
fun scaleX(scale: Float, centerX: Int) {
…
}

64. Functions
fun concat(s1: String, s2: String): String {
return s1 + s2
}

65. Functions
fun concat(s1: String, s2: String): String = s1 + s2

66. Functions
fun concat(s1: String, s2: String) = s1 + s2

67. Functions Overloading
fun scaleX(scale: Float, centerX: Int)
fun scaleX(scale: Float) = scale(scale, 0)

68. Function Default Arguments
fun scaleX(scale: Float, centerX: Int = 0)

69. Function Default Arguments
fun scaleX(scale: Float, centerX: Int = 0)

70. Functions
fun reformat(str: String,
normalizeCase: Boolean = true,
upperCaseFirstLetter: Boolean = true,
divideByCamelHumps: Boolean = false,
wordSeparator: Char = ' ')

71. Functions
reformat(str, true, true, false, '_')

72. Named arguments
reformat(str,
normalizeCase = true,
upperCaseFirstLetter = true,
divideByCamelHumps = false,
wordSeparator = '_')

73. Named arguments
reformat(str, wordSeparator = '_')

74. Functions
public final class DateUtils {
public static String getFullDate(Date date) {
SimpleDateFormat formatted = new SimpleDateFormat("hh:mm aa - dd MMM yy");
return formatted.format(date);
}
public static String getShortDateYear(Date date) {
SimpleDateFormat formatted = new SimpleDateFormat("dd MMM yy, hh:mm aa");
return formatted.format(date);
}
public static String getShortDate(Date date) {
SimpleDateFormat formatted = new SimpleDateFormat("dd MMM, hh:mm aa");
return formatted.format(date);
}
public static String getTimeOnly(Date date) {
SimpleDateFormat formatted = new SimpleDateFormat("hh:mm aa");
return formatted.format(date);
}
}

75. Extension Functions
fun Date.getFullDate() =
SimpleDateFormat("hh:mm aa - dd MMM yy").format(this)
fun Date.getShortDateYear() =
SimpleDateFormat("dd MMM yy, hh:mm aa").format(this)
fun Date.getShortDate() =
SimpleDateFormat("dd MMM, hh:mm aa").format(this)
fun Date.getTimeOnly() =
SimpleDateFormat("hh:mm aa").format(this)

76. Extension Functions
fun Date.getFullDate() =
SimpleDateFormat("hh:mm aa - dd MMM yy").format(this)

77. Classes

78. Classes
class Address {
}

79. Classes
class Address

80. Properties
class Address {
val id: Long = …
var name: String = …
var street: String = …
}

81. Lazy Properties
class Address {
val id: Long = …
var name: String = …
var street: String = …
val fullInfo by lazy { "$id $name $street" }
}

82. Lazy Properties
val fullInfo by lazy { "$id $name $street" }

83. Lazy Properties
val fullInfo by lazy { "$id $name $street" }

84. Lazy Properties
val fullInfo by lazy { "$id $name $street" }

85. Constructors
class Sample constructor(name: String)

86. Constructors
class Sample constructor(name: String)

87. Constructors
class Sample(name: String)

88. Constructors
class Sample(name: String) {
init {
// Initialization go here
}
}

89. Constructors
class Sample(val name: String)

90. Constructors
class Sample(val name: String)

91. Secondary constructors
class Sample(name: String) {
constructor(person: Person): this(person.name)
}

92. Secondary constructors
class Sample(name: String) {
constructor(person: Person): this(person.name)
}

93. Secondary constructors
class Sample(name: String) {
constructor(person: Person): this(person.name)
}

94. Secondary constructors
class Sample {
constructor(firstName: String, secondName: String) {
// Initialization go here
}
}

95. New class instance
Sample("name")
Sample(name = "name")

96. Classes defaults
• All non-abstract classes final
Effective Java, Item 17: Design and document for inheritance or else prohibit it.
• All properties final
• All functions final
• Inner classes static
• All members public by default

97. Visibility Modifiers
• private
• protected
• internal
• public

98. What is “Modules”?
• An IntelliJ IDEA module
• A Maven project
• A Gradle source set
• A set of files compiled with one invocation of the Ant Task

99. Data Classes
class Point(var x: Float, val y: Float) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (other?.javaClass != javaClass) return false
other as Point
return x == other.x && y == other.y
}
override fun hashCode() = 31 * x.hashCode() + y.hashCode()
override fun toString() = "Point(x=$x, y=$y)"
}

100. Data Classes
data class Point(var x: Float, val y: Float)

101. Data Classes
data class Point(var x: Float, val y: Float)

102. Data classes
• Implement equals(), hashCode()
• toString() of the form “Point(x=12.3,y=59.1)”
• Add componentN() functions corresponding to the properties in their order
of declaration
• Add copy() function

103. Data classes
for (point in points) {
print("(${point.x}, ${point.y})")
}

104. Destructive declaration
for ((x, y) in points) {
print("($x, $y)")
}

105. Destructive declaration
for ((x, y) in points) {
print("($x, $y)")
}

106. Enum classes
enum class Direction {
NORTH, SOUTH, WEST, EAST
}

107. Enum classes
enum class Direction {
NORTH, SOUTH, WEST, EAST
}

108. Inheritance

109. Inheritance
class Point(var x: Float, val y: Float)

110. Inheritance
open class Point(var x: Float, val y: Float)

111. Inheritance
open class Point(var x: Float, val y: Float)
class Point3D(var x: Float, var y: Float, val z: Float)

112. Inheritance
open class Point(var x: Float, val y: Float)
class Point3D(var x: Float, var y: Float, val z: Float) : Point(x, y)

113. Inheritance
open class Point(var x: Float, val y: Float)
class Point3D(x: Float, y: Float, val z: Float) : Point(x, y)

114. Inheritance
open class Point(var x: Float, val y: Float)
class Point3D : Point {
val z: Float
constructor(x: Float, y: Float, z: Float) : super(x, y) {
this.z = z
}
}

115. Interfaces

116. Interfaces
interface SampleInterface {
val prop: Int
fun bar()
fun foo()
}
class SampleClass : SampleInterface {
override val prop = 20
override fun bar() {}
override fun foo() {}
}

117. Interfaces
class SampleClass : SuperClass, Interface1, Interface2

118. Default functions
interface MyInterface {
val prop: Int
fun bar() {
print("Bar")
}
fun foo()
}

119. Collections

120. Collections
Immutable Mutable
List listOf() mutableListOf()
Set setOf() mutableSetOf()
Map mapOf() mutableMapOf()

121. Additional features
• Operator overloading
• Type Aliases
• Inline functions
• Lambdas
• High-Order Functions
• Method reference
• Sealed classes
• Delegation
• Try-with-resource
• Object expression & declaration
• DSL
• Multi value return
• Corountines
• Improved generics

122. Supporting IDE
IntelliJ IDEA Android Studio Eclipse

124. Thanks!
goo.gl/hXpK4c