Java newbie Help needed

Posted on 2004-11-11
Medium Priority
Last Modified: 2010-03-31

the last part of the code gives me a error stating could not add int to a byte array.
how could i overcome this problem

byte[] identify = {0,10,0,20,2,0};
String PR_SName = "PRS2.0";

// get the bytes for the string to be appended
byte[] prs = PR_SName.getBytes("UTF-8") ;

// create a temp array the length we will need for the two arrays joined
byte[] tmp = new byte[ identify.length + prs.length ] ;

// copy the original array into the start of our temp array
System.arraycopy( identify, 0, tmp, 0, identify.length ) ;

// copy the appended array into the end of our temp array
System.arraycopy( prs, 0, tmp, identify.length, prs.length ) ;

// set the identify array to point to our newly created temp array
identify = tmp ;

// calculating the check summ of all the values in the array identify

int sum = 0;
for(int i = 0; i< identify.length;i++)
sum += identify;
System.out.println("Sum of all the bytes =" + sum);

// I need to apeend this check sum to the end of the Identify byte[] array

byte[] checktmp = {sum / 256,sum%256};

With regards,

Question by:ashok3sep
  • 3

Expert Comment

ID: 12556692
It needs to be:

sum += identify[i];

You need to index into the array.
LVL 86

Accepted Solution

CEHJ earned 100 total points
ID: 12557330
If you need to append an array two bytes long, then you need to

a. Size the tmp array to +2 bytes long
b. Use the following code

byte[] checktmp = { (byte)(sum / 256),(byte)(sum%256) };

or more easily:

identity[identity.length - 2] = (byte)(sum / 256);
identity[identity.length - 1] = (byte)(sum % 256);

Author Comment

ID: 12583622
if i have a following code

int sum = 433;
byte[] checksum = {(byte)(sum / 256) ,(byte)(sum % 256) };
System.out.println("Higher order byte = " + (byte)(sum / 256));
System.out.println("Lower order byte = " + (byte)(sum % 256));

when i print it i have a negative value for the lower order byte

but i like to have a positive value
how could i acheive it

with regards,

LVL 86

Expert Comment

ID: 12587420
>>when i print it i have a negative value for the lower order byte

byte is a signed value, so you must 'unsign' it:

System.out.println("Lower order byte = " + ((byte)(sum % 256)) & 0xFF);

LVL 86

Expert Comment

ID: 12587423

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