How to convert each char in string to 8 bit int? JAVA

Question

I've been suggested a TCP-like checksum, which consists of the sum of the (integer) sequence and ack field values, added to a character-by-character sum of the payload field of the packet (i.e., treat each character as if it were an 8 bit integer and just add them together).

I'm assuming it would go along the lines of:

char[] a = data.toCharArray();
for (int i = 0; int < len; i++) {
   ...
}

Though I'm pretty clueless as to how I could complete the actual conversion?

My data is string, and I wish to go through the string (converted to a char array (though if there's a better way to do this let me know!)) and now I'm ready to iterate though how does one convert each character to an int. I will then be summing the total.

simple: in your for loop: int val = a[i];

ControlAltDel
– ControlAltDel

2019-03-27 14:56:06 +00:00
Commented Mar 27, 2019 at 14:56 — ControlAltDel
– ControlAltDel, Commented Mar 27, 2019 at 14:56
and this converts the current character in the loop?

bemzoo
– bemzoo

2019-03-27 14:57:27 +00:00
Commented Mar 27, 2019 at 14:57 — bemzoo
– bemzoo, Commented Mar 27, 2019 at 14:57

Joop Eggen · Accepted Answer · 2019-03-27 15:08:45Z

3

As String contains Unicode, and char is a two-byte UTF-16 implementation of Unicode, it might be better to first convert the String to bytes:

byte[] bytes = data.getBytes(StandardCharsets.UTF_8);
data = new String(bytes, StandardCharsets.UTF_8); // Inverse.

int crc = 0;
for (byte b : bytes) {
    int n = b & 0xFF; // An int 0 .. 255 without sign extension
    crc ^= n;
}

Now you can handle any Unicode content of a String. UTF-8 is optimal when sufficient ASCII letters are used, like Chinese HTML pages. (For a Chinese plain text UTF-16 might be better.)

edited Mar 27, 2019 at 15:08

answered Mar 27, 2019 at 14:57

Joop Eggen

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4 Comments

bemzoo Over a year ago

How would I now go from [B@106d69c to an integer?

Joop Eggen Over a year ago

byte is a signed 8 bit integer, hence you are almost there. I added an example for loop. The toString of a byte array is just its type code [B (array of byte) and object address/handle @106d69c

bemzoo Over a year ago

The above loop provides me with an outcome of 0, I don't understand why you would use the XOR operand?

Joop Eggen Over a year ago

That was just an example, the calculation I leave as your effort (+=, and that ack field). So not to suggest having a result; info fails.

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