Summary - File I/O

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.

Exercise 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.

Show example 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)
}

Exercise 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.

Show example solution

fun main() {
    val f = File("gunluk.txt")
    f.writeText("start")
    f.appendText(" - more")
    println(f.readText())
}

Test yourself

Which overwrites a file?
- readText
- writeText
- appendText
- readLines
Show answer

writeText — writeText erases the existing content and writes the new one.
Match the file methods

File("a.txt")

Path representation
readText()

Reads all content
writeText()

Overwrites
appendText()

Appends to end

Next lesson: package

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