fun with permissions

expected-output.txt

0600 (.rw-------) -> 0700 (.rwx------)
0755 (.rwxr-xr-x) -> 0755 (.rwxr-xr-x)
0660 (.rw-rw----) -> 0770 (.rwxrwx---)
0664 (.rw-rw-r--) -> 0775 (.rwxrwxr-x)
0666 (.rw-rw-rw-) -> 0777 (.rwxrwxrwx)
0622 (.rw--w--w-) -> 0733 (.rwx-wx-wx)
0777 (.rwxrwxrwx) -> 0777 (.rwxrwxrwx)

main.java

class Main {
  static int ownerRead = 04 << 6;
  static int ownerWrite = 02 << 6;
  static int ownerExecute = 01 << 6;
  
  static int groupRead = 04 << 3;
  static int groupWrite = 02 << 3;
  static int groupExecute = 01 << 3;

  static int otherRead = 04;
  static int otherWrite = 02;
  static int otherExecute = 01;

  static int noop = 00;

  public static void main(String args[]) {
    checkPermElevation("0600");
    checkPermElevation("0755");
    checkPermElevation("0660");    
    checkPermElevation("0664");
    checkPermElevation("0666");
    checkPermElevation("0622");
    checkPermElevation("0777");
  }

  static void checkPermElevation (final String oct) {
    int p = Integer.parseInt(oct, 8);
    int elevated = safeElevatePrivileges(p);
    System.out.println(oct + " (" + toStringRepresentation(p) + ") -> 0" + Integer.toOctalString(elevated) + " (" + toStringRepresentation(elevated) + ")");
  }

  static char check(final int subject, final int octal, final char successValue) {
    return ((subject & octal) > 0) ? successValue : '-';
  }

  static String toStringRepresentation (final int p) {
    return "." +
         check(p, ownerRead, 'r') +
         check(p, ownerWrite, 'w') +
         check(p, ownerExecute, 'x') +

         check(p, groupRead, 'r') +
         check(p, groupWrite, 'w') +
         check(p, groupExecute, 'x') +
         
         check(p, otherRead, 'r') +
         check(p, otherWrite, 'w') +
         check(p, otherExecute, 'x')
    ;
  }

  static int setExecutableIfOtherCanReadOrWrite (final int p) {
    final boolean canReadOrWrite = (p & otherRead) + (p & otherWrite) > 0;

    return canReadOrWrite ? otherExecute : noop;
  }

  static int setExecutableIfGroupCanReadOrWrite (final int p) {
    final boolean canReadOrWrite = (p & groupRead) + (p & groupWrite) > 0;

    return canReadOrWrite ? groupExecute : noop;
  }

  static int setExecutableForOwner (final int p) {
    return ownerExecute;
  }

  static int safeElevatePrivileges (final int p) {
    return p
      | ownerExecute
      | setExecutableIfGroupCanReadOrWrite(p)
      | setExecutableIfOtherCanReadOrWrite(p)
    ;
  }
}