The java.util.zip package can be used to create a checksum. : Checksum « File « Java Tutorial

1. Java Tutorial
2. File
3. Checksum

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.util.Arrays;
import java.util.zip.CRC32;

public class Main {
  public static void main(String[] args) throws Exception{
    BufferedInputStream is = new BufferedInputStream(new FileInputStream("a.exe"));
    byte[] bytes = new byte[1024];
    int len = 0;

    while ((len = is.read(bytes)) >= 0) {
      new CRC32().update(bytes, 0, len);
    }
    is.close();
    System.out.println(Arrays.toString(bytes));

  }
}