How to Use BufferedReader in Kotlin: Simple Guide

In Kotlin, you can use bufferedReader() to read text from an input stream efficiently by wrapping it in a buffered reader. This allows you to read lines or characters easily using methods like readLine().

Syntax

The bufferedReader() function creates a buffered reader from an input source like a file or input stream. You can then use methods like readLine() to read text line by line.

Example parts:

• inputStream.bufferedReader(): Wraps the input stream with a buffered reader.
• readLine(): Reads one line of text.
• use { }: Ensures the reader is closed automatically after use.

kotlin

val reader = inputStream.bufferedReader()
val line = reader.readLine()

Example

This example reads lines from standard input until an empty line is entered, then prints each line.

kotlin

fun main() {
    println("Enter text lines (empty line to stop):")
    val lines = mutableListOf<String>()
    System.`in`.bufferedReader().use { reader ->
        while (true) {
            val line = reader.readLine() ?: break
            if (line.isEmpty()) break
            lines.add(line)
        }
    }
    println("You entered:")
    lines.forEach { println(it) }
}

Output

Enter text lines (empty line to stop):
Hello
World

You entered:
Hello
World

Common Pitfalls

Common mistakes when using bufferedReader() include:

• Not closing the reader, which can cause resource leaks. Use use { } to close automatically.
• Assuming readLine() never returns null. It returns null at the end of input.
• Reading input without checking for empty lines or end of stream, causing infinite loops.

kotlin

/* Wrong way: Not closing reader and ignoring null */
val reader = System.`in`.bufferedReader()
while (true) {
    val line = reader.readLine() // no null check
    println(line) // may print null and cause issues
}

/* Right way: Using use and null check */
System.`in`.bufferedReader().use { reader ->
    while (true) {
        val line = reader.readLine() ?: break
        println(line)
    }
}

Quick Reference

Summary tips for using bufferedReader() in Kotlin:

• Wrap input streams or files with bufferedReader() for efficient reading.
• Use readLine() to read text line by line.
• Always use use { } to close the reader automatically.
• Check for null from readLine() to detect end of input.

Key Takeaways

Use bufferedReader() to wrap input streams for efficient text reading.

Always close the buffered reader using use { } to avoid resource leaks.

Check for null from readLine() to handle end of input safely.

Read input line by line with readLine() for simple text processing.