Putting it together
- Kotlin course
- Intermediate
- Lesson 23/116
- 6 min
Combine helper functions into a library.
Putting it together
This final lesson combines all helpers under a single runAll method. The Helpers object holds a report method that calls every extension.
The project now has: greet inside object Helpers; the String.titleCase, Int.squared and LocalDate.isWeekend extensions. In this lesson you add a fun runAll(): String method to Helpers. It calls every helper and merges the results into a single string. main just calls Helpers.runAll().
runAll and main
The runAll method calls every helper in order and joins the results with |. main just calls println(Helpers.runAll()).
Example: fun runAll(): String { val g = greet("Alex"); val t = "hello world".titleCase(); val s = 5.squared(); val w = LocalDate.of(2024, 1, 6).isWeekend(); return "$g | $t | $s | $w" }. This presents the output of every helper in a single string. main stays simple; all work is collected in the library. This structure is the essence of real library design.
Practice Add the runAll method and simplify main
Keep the existing library. Add a fun runAll(): String method inside the Helpers object. Its body calls in order greet("Alex"), "hello world".titleCase(), 5.squared() and LocalDate.of(2024, 1, 6).isWeekend(), then joins the results with | and returns them: "$g | $t | $s | $w". main just calls println(Helpers.runAll()).
Starter code
import java.time.LocalDate
object Helpers {
fun greet(name: String): String {
return "Hello, $name!"
}
}
fun String.titleCase(): String {
return split(" ").joinToString(" ") { word ->
word.lowercase().replaceFirstChar { it.uppercase() }
}
}
fun Int.squared(): Int {
return this * this
}
fun LocalDate.isWeekend(): Boolean {
val day = dayOfWeek.value
return day == 6 || day == 7
}
fun main() {
println(Helpers.greet("Alex"))
println("hello world".titleCase())
println(5.squared())
println(LocalDate.of(2024, 1, 6).isWeekend())
}
// Add a runAll method inside Helpers
// call every helper, join with |
// main just calls Helpers.runAllSample solution
import java.time.LocalDate
object Helpers {
fun greet(name: String): String {
return "Hello, $name!"
}
fun runAll(): String {
val g = greet("Alex")
val t = "hello world".titleCase()
val s = 5.squared()
val w = LocalDate.of(2024, 1, 6).isWeekend()
return "$g | $t | $s | $w"
}
}
fun String.titleCase(): String {
return split(" ").joinToString(" ") { word ->
word.lowercase().replaceFirstChar { it.uppercase() }
}
}
fun Int.squared(): Int {
return this * this
}
fun LocalDate.isWeekend(): Boolean {
val day = dayOfWeek.value
return day == 6 || day == 7
}
fun main() {
println(Helpers.runAll())
}Expected output
Hello, Alex! | Hello World | 25 | true
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Where is the <code>runAll</code> method added in the integration lesson?
- As a String extension
- As an Int extension
- As a LocalDate extension
- Inside the Helpers object Correct answer
Explanation: runAll is added as a method of the Helpers object.
2 Match all helpers
| Term | Meaning |
|---|---|
Helpers.greet |
Greeting |
String.titleCase |
Title format |
Int.squared |
Squaring |
LocalDate.isWeekend |
Weekend check |
3 Complete the main body
fun main() {
println(Helpers.____())
}fun main() {
println(Helpers.runAll())
}Explanation: runAll calls every helper.