Compare two files to check equality in Kotlin

This post will discuss how to compare the contents of two files to check whether they are equal in Kotlin.

1. Using `Files` class

A simple solution is to read the entire file into a string and compare both strings for equality. The idea is to use the Files.readString() function to read all content from a file into a string, and then check the string’s equality using the contentEquals() function.

import java.io.File

import java.nio.file.Files

import java.nio.file.Path

private fun isEqual(firstFile: Path, secondFile: Path): Boolean {

if (Files.size(firstFile) != Files.size(secondFile)) {

return false

}

val first = Files.readString(firstFile)

val second = Files.readString(secondFile)

return first!!.contentEquals(second)

}

fun main() {

val firstFile = File("/files/first.txt")

val secondFile = File("/files/second.txt")

val isEqual = isEqual(firstFile.toPath(), secondFile.toPath())

if (isEqual) {

println("Files are equal")

} else {

println("Files are not equal")

}

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Alternately, you can read all the bytes from the files into byte arrays and compare both byte arrays for equality. This can be done using the Files.readAllBytes() function, as shown below:

import java.io.File

import java.nio.file.Files

import java.nio.file.Path

private fun isEqual(firstFile: Path, secondFile: Path): Boolean {

if (Files.size(firstFile) != Files.size(secondFile)) {

return false

}

val first = Files.readAllBytes(firstFile)

val second = Files.readAllBytes(secondFile)

return first.contentEquals(second)

}

fun main() {

val firstFile = File("/files/first.txt")

val secondFile = File("/files/second.txt")

val isEqual = isEqual(firstFile.toPath(), secondFile.toPath())

if (isEqual) {

println("Files are equal")

} else {

println("Files are not equal")

}

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2. Using `BufferedReader`

Reading the entire contents of a file in a String or a byte array is not preferable for large files, since it can exhaust the heap memory. For large files, consider using the BufferedReader to read the files chunk-by-chunk.

The following solution demonstrates its usage by reading the file character-by-character with the BufferedReader#read() function:

import java.io.File

import java.nio.file.Files

import java.nio.file.Path

private fun isEqual(firstFile: Path, secondFile: Path): Boolean {

if (Files.size(firstFile) != Files.size(secondFile)) {

return false

}

Files.newBufferedReader(firstFile).use { bf1 ->

Files.newBufferedReader(secondFile).use { bf2 ->

var ch: Int

while (bf1.read().also { ch = it } != -1) {

if (ch != bf2.read()) {

return false

}

return true

}

fun main() {

val firstFile = File("/files/first.txt")

val secondFile = File("/files/second.txt")

val isEqual = isEqual(firstFile.toPath(), secondFile.toPath())

if (isEqual) {

println("Files are equal")

} else {

println("Files are not equal")

}

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Alternately, you can read a file line-by-line with BufferedReader#readLine() function:

import java.io.File

import java.nio.file.Files

import java.nio.file.Path

private fun isEqual(firstFile: Path, secondFile: Path): Boolean {

if (Files.size(firstFile) != Files.size(secondFile)) {

return false

}

Files.newBufferedReader(firstFile).use { bf1 ->

Files.newBufferedReader(secondFile).use { bf2 ->

var line: String

while (bf1.readLine().also { line = it } != null) {

if (line !== bf2.readLine()) {

return false

}

return true

}

fun main() {

val firstFile = File("/files/first.txt")

val secondFile = File("/files/second.txt")

val isEqual = isEqual(firstFile.toPath(), secondFile.toPath())

if (isEqual) {

println("Files are equal")

} else {

println("Files are not equal")

}

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That’s all about comparing the contents of two files for determining equality in Kotlin.

Compare two files to check equality in Kotlin

1. Using Files class

2. Using BufferedReader

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1. Using `Files` class

2. Using `BufferedReader`