Java12 introduced a mismatch method to java.nio.file.Files Class.

Mismatch compares two files and returns the position of the matched first content byte of a file. If there is no match, Returns -1.

Here is an example.

    public static long mismatch(Path path, Path path2) throws IOException

The below use case return -1 and If two files are matched,

  • if both files are referring to the same file and location
  • original and copied files
  • same content in different files in different locations
  • two-path files of the same size and content is the same
  • soft and hard-linked files of the same content

Below are mismatched cases and return long number.

  • First occurrence of mismatched content
  • The small size files’ mismatched position is returned

Here is an example

package java12;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class FilesMisMatch {
    public static void main(String[] args) {
        //Path object with given file in File System
        Path path1= Paths.get("a:\\", "test1.txt");
        Path path2= Paths.get("a:\\", "test2.txt");
        Path path3= Paths.get("a:\\", "test3.txt");

        try {
            Files.writeString(path1, "Test content inserted into a file", StandardOpenOption.CREATE);
            Files.writeString(path2, "Test content inserted into a file", StandardOpenOption.CREATE);
            Files.writeString(path3, "Test content inserted into a file 1", StandardOpenOption.CREATE);

            long result = Files.mismatch(path1, path2);
            System.out.println("Compare path1 and path2 = " + result); // returns -1

            result = Files.mismatch(path2, path3);
            System.out.println("Compare path2 and path3 = " + result); // returns 33

        } catch (IOException e) {



Compare path1 and path2 = -1
Compare path2 and path3 = 33