Need help to create byte array

[Roedy Green]

byte[] bits = new byte[56];

not to nitpick, but it'd be new byte[0xAA, 0xAA, 0xAA, 0xAA, 0xAA,
0xAA, 0xAA] for 56 bits.

It looks originally as if he wanted addressibility so bad he was
willing to store only one bit per byte.

 

[ami]

So should I do the following:

1.Take parameters as string or int
2. Convert it into bytes and put it into array.
3. send that array to the client
4. read byte convert it to back to print in readable format.

 

[Tex]

I am a new bee in java, I am simulating ethernet frame for which I

need to create byte array of 0'and 1's. Ethernet frame has 56 bit
preamble of alternating 1's and 0's. I need to send this field and
other with similar format over the socket. Can any one help and explain
me how to create byte array for 1 and 0?

I understand how to declare array. I am famalier with int,long double
array but I am confused for byte array. How do I insert 10101010 for
first byte in byte array? If possible can you give some code?

Assuming you understand binary, decimal & hex encoding.

1. Don't need array to send 10101010101010101010110... for 56 bits (7
bytes):
Problem is that Java compiler won't let you set byte b = 0xAA. You can
have such a
byte, but can't initialize it with Hex. It would be nice, but tuff
luck. I'm sure Java compiler
guys thought they were helping me.

So, set byte = -86 which compiler will allow and byte = -86 dec =
10101010 binary
= 0xAA hex. All same thing in memory, thus:

byte b = -86;
for (int i = 0; i < 7; i++) Send(b);

2. Suppose you need to send arbitraty bit patterns in bytes. For all bit
patterns less than
128 you can just use hex, e.g. byte b = 0x3C; For all bit patterns with
msb = 1, you need
to find equivalent decimal negative representation. Or you could set
up a byte array
containing all the 256 bit patterns and use an int index which you can
set with hex.

a. byte[] b = { 0, // 0. Dec value for byte 0x00
= 0000 0000
. . . . . .
126, // 126. Dec Value for byte
0x7F = 0111 1111
-128, // 127. Dec Value for byte
0x80 = 1000 0000
-127, // 128. Dec Value for byte
0x81 = 1000 0001
. . . . . .
-1}; // 255. Dec Value for byte
0xFF = 1111 1111


b. Same array with less typing and less bytecode:
byte[] b = new byte[256];
byte bPos = 0;
byte bNeg = -128;
for ( int i = 0; i <= 0x7F; i++) b = bPos++;
for ( int i = 0x80; i <= 0xFF; i++) b = bNeg++;

Now, with our 256-byte byte array set we can send an abritray bit pattern
and use Hex.
Suppose we want to send 16 bits: 1000 1111 0001 0000 (i.e. 0x8F, 0x10).
Create an
int array for the 2-byte field/frame or whatever you wanna call it as:

int[] iField = {0x8F, 0x10};
for (int i = 0; i < iField.length; i++) Send(b[iField]);

where integers that the compiler will let us set the way we want are used
as indexes into
the 256-byte array.

Wanna print out a byte? Working with bits, a hex printout works well,
so:

int iHex = b[...some index we want...] & 0x00FF; //0x00FF clears any
sign extension
String s = Integer.toHexString(iHex);

--tex

 

[Tex]

Casting also works and is simple & straight forward.
Suppose we want to send 16 bits: 1000 1111 0001 0000 (i.e. 0x8F, 0x10).
Create an int array for the 2-byte field as:

int[] iField = {0x8F, 0x10}; //Java compiler allows this
for (int i = 0; i < iField.length; i++) Send((byte) iField);

--tex

 

[ami]

Thank you all .
I have success fully created byte array.
but Now my proble is I can not read that array?
can any one tell me how to read array over sockets?
I have tried following code with DataInput/output Streams without any
luck

byte[] ethFrame;
out.write(ethFrame, 0, ethFrame.length);

And tried to read on the other end with
in.read(bytes,offset, length);
or
in.readFully(bytes,offset, length);


but I could not print it out?


Can any one help me to read byte array ?


Please help me!!

 

[Roedy Green]

can any one tell me how to read array over sockets?

see http://mindprod.com/applets/fileio.html