Hola quiero guardar los strings en un tipo byte[], pero el operador + no lo soporta
String message = "hola1";
String message2="hola2";
String message3="hola3";
byte[] envio=message.getBytes("UTF-8")+message2.getBytes("UTF-8");
Aquí ponen varias formas de concatenar arrays: https://stackoverflow.com/questions/5513152/easy-way-to-concatenate-two-byte-arrays (https://stackoverflow.com/questions/5513152/easy-way-to-concatenate-two-byte-arrays)