BufferedReader builderBufferedReader is created without explicitely stating a Charset it uses, it will use StandardCharsets.UTF_8.BufferedWriter builderBufferedWriter is created without explicitely stating a Charset it uses, it will use StandardCharsets.UTF_8.BufferedReader (according to previously parameters set).BufferedReaderBuilder.charset is not set, then a BufferedReaderBuilder.DEFAULT_CHARSET will be used.BufferedWriter, according to previously set parameters.