问为什么`SmsMessage.createFromPdu`返回一个数组？

EN

private static Map<String, String> RetrieveMessages(Intent intent) {
    Map<String, String> msg = null; 
    SmsMessage[] msgs;
    Bundle bundle = intent.getExtras();

    if (bundle != null && bundle.containsKey("pdus")) {
        Object[] pdus = (Object[]) bundle.get("pdus");

        if (pdus != null) {
            int nbrOfpdus = pdus.length;
            msg = new HashMap<String, String>(nbrOfpdus);
            msgs = new SmsMessage[nbrOfpdus];

            // There can be multiple SMS from multiple senders, there can be a maximum of nbrOfpdus different senders
            // However, send long SMS of same sender in one message
            for (int i = 0; i < nbrOfpdus; i++) {
                msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]);

                String originatinAddress = msgs[i].getDisplayOriginatingAddress();

                // Check if index with number exists                    
                if (!msg.containsKey(originatinAddress)) { 
                    // Index with number doesn't exist                                               
                    // Save string into associative array with sender number as index
                    msg.put(msgs[i].getOriginatingAddress(), msgs[i].getDisplayMessageBody()); 

                } else {    
                    // Number has been there, add content but consider that
                    // msg.get(originatinAddress) already contains sms:sndrNbr:previousparts of SMS, 
                    // so just add the part of the current PDU
                    String previousparts = msg.get(originatinAddress);
                    String msgString = previousparts + msgs[i].getMessageBody();
                    msg.put(originatinAddress, msgString);
                }
            }
        }
    }

    return msg;
}