The Kotlin Programming Language

Kotlin Companion Objects

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In this lesson, you'll learn how to create a companion object in your class, why you'd want them and how to use them in other classes.

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Lessons in The Kotlin Programming Language

1. Installing the IntelliJ IDE for Kotlin Development

2. Creating a Kotlin File in IntelliJ

3. How to Update the Kotlin Plugin in IntelliJ

4. Kotlin Hello World

5. Creating Variables in Kotlin

6. Creating Read Only Variables in Kotlin

7. Providing the Type on Kotlin Variables

8. Kotlin Data Types: Numbers

9. Kotlin Data Types: String and Char

10. Kotlin String Interpolation and Triple Quotes

11. Kotlin Data Types: Boolean

12. Kotlin Conditionals: If/Else

13. Kotlin Conditionals: Single line if/else

14. Kotlin Conditionals: Truth Tables

15. Kotlin Structural Equality

16. Kotlin Referential Equality

17. Kotlin Nullable Types

18. Kotlin Nullable Safe Calls

19. Kotlin Elvis Operator

20. How to Create a Function in Kotlin

21. Returning a value from a Kotlin Function

22. Kotlin Functions inside of other Functions

23. Kotlin Single Line Expressions

24. Kotlin Function Arguments

25. Kotlin Named Parameters in Functions

26. Kotlin Default Arguments

27. Kotlin Refactoring to New Lines and Named Arguments in IntelliJ

28. Kotlin Varargs: Providing Multiple Arguments of the Same Type

29. Kotlin Function Overloading

30. How to Create a Class in Kotlin

31. Kotlin Class Primary Constructor

32. Kotlin Class with Multiple Constructors

33. Kotlin Init Block

34. Kotlin Class Properties

35. Kotlin Read-Only Class Properties

36. Kotlin Overriding the Property Getter

37. Kotlin Overriding the Property Setter

38. Kotlin Multiple Properties in a Class

39. Kotlin Class Functions

40. Kotlin Companion Objects

41. How to Create a Singleton in Kotlin

42. Declaring Constants in Kotlin

43. Kotlin lateinit Modifier

44. Kotlin Nested Classes

45. Kotlin Inner Classes

46. How to Create an Enum in Kotlin

47. Kotlin Enum Constructor Parameters

48. Creating Abstract Functions inside of Kotlin Enums

49. Iterating Over Enum Values in Kotlin

50. Adding Static Methods to Kotlin Enums

51. Kotlin Conditionals - The Kotlin when statement

52. Kotlin when Statement - Exhaustive vs Non-exhaustive

53. Kotlin Data Classes

54. Kotlin Data Classes - Parameterless Constructors

55. Kotlin Data Class Component1, Component2, ComponentN

56. Kotin Data Class Destructuring

57. Copying Kotlin Data Classes

58. Kotlin Pair and Triple Data Classes

59. Kotlin Protected Modifier for Variables

60. Kotlin Protected Modifier for Methods

61. Kotlin Internal Modifier

62. How to Create an Abstract Class in Kotlin

63. How to Implement an Abstract Class in Kotlin

64. Kotlin Abstract Classes - Using Abstract Classes as an Abstraction

65. What are Kotlin Interfaces Used For?

66. Kotlin Interfaces - Creating an Interface in Kotlin

67. Kotlin Interfaces - Implementing an Interface in Kotlin

68. Kotlin Interfaces Example - Multiple File Systems

69. Kotlin Anonymous Interfaces

70. Creating Arrays in Kotlin

71. Creating a List in Kotlin

72. Creating Mutable Lists in Kotlin

73. Filtering a List in Kotlin

74. Finding Items in a Kotlin List

75. Kotlin FilterNot on a List

76. Creating a New Kotlin List from an Existing Kotlin List

77. How to Flatten a List or an Array in Kotlin

78. Combining Multiple Immutable Lists in Kotlin

79. Kotlin List map Operator

80. Kotlin map vs. flatMap

81. Kotlin Set - A List with No Duplicates

82. Kotlin For Loop

83. Kotlin While Loop

84. Kotlin forEach Collection Iteration

85. Combine List into a Unique List with the union operator

86. Kotlin Iterating over a List with an Index with forEachIndex

87. Kotlin Ranges

88. How To Create a Map in Kotlin

89. How to create a Mutable Map in Kotlin

90. Filtering and Transforming Maps in Kotlin

91. Kotlin mapNotNull - Removing null items from a map

92. Generate Large Sequences and Lists in Kotlin with generateSequence

93. Kotlin Performance - Measuring performance with measureNanoTime

94. Kotlin Sequences - Improving performance with Kotlin Sequences

95. Kotlin - List vs. Set vs. Map

96. The Kotlin Ternary Operator

97. Kotlin Double Bang Operator !!

98. Kotlin requireNotNull - Forcing something that is nullable to be not null

99. Kotlin checkNotNull - Checking that a value is not null

100. Filter a list for Not Null Values in Kotlin with filterNotNull

101. Kotlin Type Hierarchy and Kotlin Type Checking with 'is'

102. Casting in Kotlin

103. Kotlin Safe Casting

104. Understanding Generics with Lists and Maps in Kotlin

105. Kotlin Generic Class - How to Create a Generic Class

106. Throwing an Exception in Kotlin

107. Kotlin - Creating a Custom Exception

108. Kotlin Try Catch Statement

109. Catching Multiple Exception Types in Kotlin

110. Try/Catch/Finally in Kotlin

111. Kotlin Try/Catch vs Try/Finally

112. Kotlin typealias - How to create a typealias in Kotlin

113. Creating a Kotlin Extension Function

114. Kotlin Lazy Evaluation

115. Kotlin Lazy Initializer Block

116. Kotlin Packages and Imports

117. Kotlin Type Inference

118. Kotlin Lambdas - Understanding Simple Lambda Expressions

119. Kotlin Lambdas - Lambdas as Function Parameters

120. Kotlin Lambdas - Passing Values to Lambda Expression Function Parameters

121. Kotlin Lambdas - Using Underscores to Signify Unused Parameters

122. Kotlin Lambdas - The 'it' parameter

123. Kotlin JVM Interop - Calling Kotlin from Java

124. Kotlin JVM Interop - Calling Java from Kotlin

125. Kotlin JVM Interop - Calling a Kotlin Extension Function from Java

126. Kotlin JVM Interop - The JvmName Annotation

127. Run Kotlin Code Anywhere with Kotlin Main Functions

128. Working with the Kotlin REPL

129. Kotlin Simple Calculator Project - Creating the Project and Main Function

130. Kotlin Simple Calculator Project - Reading User Input with readLine()

131. Kotlin Simple Calculator Project - Building the Calculator Logic

132. Kotlin Simple Calculator Project - Adding Validation to your Simple Calculator

133. Kotlin Simple Calculator Project - Compiling to a JAR File

134. Kotlin Playground and Kotlin Koans