private String getExtensionByOs(String os) {
        if (os == null || os.isEmpty()) return "";
        else if (os.contains("win")) return ".exe";
        return "";
    }
private String getExtensionByOs ( String os ) { if ( os == null || os . isEmpty ( ) ) return "" ; else if ( os . contains ( "win" ) ) return ".exe" ; return "" ; }
Return the Os specific extension

@param os: operating system name