Summary - File I/O
- Kotlin course
- Intermediate
- Lesson 99/116
- 5 min
Combine readText, writeText and readLines to write a notes app.
Summary - File I/O
In this group you learned the file path with java.io.File, reading all content with readText, overwriting with writeText, getting a list of lines with readLines and appending to the end with appendText.
Now you will combine them: first write to a file and walk the lines with readLines, then use writeText and appendText together. This structure is the foundation of small file-based applications in Kotlin. Later, formats such as JSON and CSV are built on top of these methods.
Practice Combine writeText and readLines
Create val f = File("liste.txt"). Write three lines with f.writeText("apple\npear\nbanana"). Read the lines with val lines = f.readLines(). Print the count with println(lines.size); then loop with for (line in lines) and println each line. Add the import java.io.File import.
Starter code
import java.io.File
// File object for path liste.txt
// write three fruit lines with writeText
// read with readLines, print size then each line
fun main() {
// write here
}Sample solution
fun main() {
val f = File("liste.txt")
f.writeText("apple\npear\nbanana")
val lines = f.readLines()
println(lines.size)
for (line in lines) println(line)
}Expected output
3 apple pear banana
Practice Combine writeText and appendText
Create val f = File("gunluk.txt"). Start with f.writeText("start"). Append with f.appendText(" - more"). Read and print with println(f.readText()). Add the import java.io.File import.
Starter code
import java.io.File
// File object for path gunluk.txt
// start with writeText("start")
// append with appendText(" - more")
// read with readText and println
fun main() {
// write here
}Sample solution
fun main() {
val f = File("gunluk.txt")
f.writeText("start")
f.appendText(" - more")
println(f.readText())
}Expected output
start - more
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which overwrites a file?
- readText
- writeText Correct answer
- appendText
- readLines
Explanation: writeText erases the existing content and writes the new one.
2 Match the file methods
| Term | Meaning |
|---|---|
File("a.txt") |
Path representation |
readText() |
Reads all content |
writeText() |
Overwrites |
appendText() |
Appends to end |