Changing a byte in a byte array???? HELP

Hey I have the following code
     String plainString = new String();
     byte[] byt = new byte[0];
     byte change;
     try
          int length = (int)(keyf.length());
          byt = new byte[(length++)];
          keyf.readFully(byt);
          keyf.seek(0);
     }catch(IOException e){System.err.println(e);}And I want to edit the byt array at position (length--) and add the character "," there. Also changing the byt array at its current position to eof. Anyone know what to do???

Make a new array with a size of length+1.byt = new byte[(length++)];
keyf.readFully(byt);
byte[] b2 = new byte[byt.length+1];
System.arraycopy(byt, 0, b2, 0, byt.length);
b2[b2.length - 1] = (byte)',';

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Hi can anybody help me calculate the number of bytes in a hexidecimal array ie:
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Hi,
I'm not sure if you want to count the bytes or sum the array. But here's an example of both:
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Attachments:
ByteCount.vi ‏18 KB

Converting bytes to shorts using arrays and NIO buffers - is this a bug?

I'm benchmarking the various methods for converting a sequence of bytes into shorts. I tried copying a byte array, a direct NIO buffer and a non-direct NIO buffer to a short array (using little-endian byte order). My results were a little confusing to me. As I understand it, direct buffers are basically native buffers - allocated by the OS instead of on the runtime's managed heap, hence their higher allocation cost and ability to perform quicker IO with channels that can use them directly. I also got the impression that non-direct buffers (which have a backing array) are basically just regular Java arrays wrapped in a ByteBuffer.
I didn't expect a huge difference between the results of my three tests, though I thought the two NIO methods might perform a bit quicker if the virtual machine was smart enough to notice that little-endian is my system's native byte order (hence allowing the chunk of memory to simply be copied, rather than applying a bunch of shifts and ORs to the bytes). Conversion with the direct NIO buffer was indeed faster than my byte array method, however the non-direct NIO buffer performed over ten times slower than even my array method. I can see it maybe performing a millisecond or two slower than the array method, what with virtual function call overhead and a few if checks to see what byte order should be used and what not, but shouldn't that method basically be doing exactly the same thing as my array method? Why is it so horribly slow?
Snippet:
import java.nio.*;
public class Program {
public static final int LOOPS = 500;
public static final int BUFFER_SIZE = 1024 * 1024;
public static void copyByteArrayToShortArrayLE(byte[] buffer8, short[] buffer16) {
    for(int i = 0; i < buffer16.length; i += 2){
      buffer16[i >>> 1] = (short) ((buffer8[i] & 0xff) | ((buffer8[i + 1] & 0xff) << 8));
public static void main(String[] args) {
    short[] shorts = new short[BUFFER_SIZE >>> 1];
    byte[] arrayBuffer = new byte[BUFFER_SIZE];
    ByteBuffer directBuffer = ByteBuffer.allocateDirect(BUFFER_SIZE).order(ByteOrder.LITTLE_ENDIAN);
    ByteBuffer nonDirectBuffer = ByteBuffer.allocate(BUFFER_SIZE).order(ByteOrder.LITTLE_ENDIAN);
    long start;
    start = System.currentTimeMillis();
    for(int i = 0; i < LOOPS; ++i) copyByteArrayToShortArrayLE(arrayBuffer, shorts);
    long timeArray = System.currentTimeMillis() - start;
    start = System.currentTimeMillis();
    for(int i = 0; i < LOOPS; ++i) directBuffer.asShortBuffer().get(shorts);
    long timeDirect = System.currentTimeMillis() - start;
    start = System.currentTimeMillis();
    for(int i = 0; i < LOOPS; ++i) nonDirectBuffer.asShortBuffer().get(shorts);
    long timeNonDirect = System.currentTimeMillis() - start;
    System.out.println("Array:      " + timeArray);
    System.out.println("Direct:     " + timeDirect);
    System.out.println("Non-direct: " + timeNonDirect);
}Result:
Array:      328
Direct:     234
Non-direct: 4860

Using JDK1.6.0_18 on Ubuntu 9.1 I typically get
Array: 396
Direct: 550
Non-direct: 789
I think your tests are a little too short for accurate timings because they are likely to be significantly influenced by the JIT compilation.
If I change to use a GIT warmup i.e.
public static final int LOOPS = 500;
    public static final int WARMUP_LOOPS = 500;
    public static final int BUFFER_SIZE = 1024 * 1024;
    public static void copyByteArrayToShortArrayLE(byte[] buffer8, short[] buffer16)
        for (int i = 0; i < buffer16.length; i += 2)
            buffer16[i >>> 1] = (short) ((buffer8[i] & 0xff) | ((buffer8[i + 1] & 0xff) << 8));
    public static void main(String[] args)
        short[] shorts = new short[BUFFER_SIZE >>> 1];
        byte[] arrayBuffer = new byte[BUFFER_SIZE];
        ByteBuffer directBuffer = ByteBuffer.allocateDirect(BUFFER_SIZE).order(ByteOrder.LITTLE_ENDIAN);
        ByteBuffer nonDirectBuffer = ByteBuffer.allocate(BUFFER_SIZE).order(ByteOrder.LITTLE_ENDIAN);
        long start = 0;
        for (int i = -WARMUP_LOOPS; i < LOOPS; ++i)
            if (i == 0)
                start = System.currentTimeMillis();
            copyByteArrayToShortArrayLE(arrayBuffer, shorts);
        long timeArray = System.currentTimeMillis() - start;
        for (int i = -WARMUP_LOOPS; i < LOOPS; ++i)
            if (i == 0)
                start = System.currentTimeMillis();
            directBuffer.asShortBuffer().get(shorts);
        long timeDirect = System.currentTimeMillis() - start;
        for (int i = -WARMUP_LOOPS; i < LOOPS; ++i)
            if (i == 0)
                start = System.currentTimeMillis();
            nonDirectBuffer.asShortBuffer().get(shorts);
        long timeNonDirect = System.currentTimeMillis() - start;
        System.out.println("Array:      " + timeArray);
        System.out.println("Direct:     " + timeDirect);
        System.out.println("Non-direct: " + timeNonDirect);
    }then I typically get
Array: 365
Direct: 528
Non-direct: 750
and if I change to 50,000 loops I typically get
Array: 37511
Direct: 57199
Non-direct: 73913
You also seem to have a bug in your copyByteArrayToShortArrayLE() method. Should it not be
public static void copyByteArrayToShortArrayLE(byte[] buffer8, short[] buffer16)
        for (int i = 0; i < buffer8.length; i += 2)
            buffer16[i >>> 1] = (short) ((buffer8[i] & 0xff) | ((buffer8[i + 1] & 0xff) << 8));
    }Edited by: sabre150 on Jan 27, 2010 9:07 AM

Best way to append null bytes to a byte array?

I have a fixed length byte array and need to add two null bytes to its end. I have an implementation that I wrote to do this, though I was wondering whether someone could improve on what I have:
public byte[] appendNullBytes( byte[] bytes ) {
   byte[] copyBytes = new byte[bytes.length+2];
   System.arraycopy(bytes, 0, copyBytes, 0, bytes.length);
   copyBytes[copyBytes.length-1] = 0;
   copyBytes[copyBytes.length-2] = 0;
   return copyBytes
}

ajmasx wrote:
jverd wrote:
ajmasx wrote:
jverd wrote:
Those aren't null bytes, they're zero bytes. A bytes can never have the value null in Java.I was using the term null interchangeably with 'zero', Which is not generally applicable in Java.Well it all depends what you are doing:
- A null is a zero value.Not in general in Java. Null is null and zero is zero.
- char c = '\0' defines a null character.Yes, that's the only use of "null" for primitive types.
- A null pointer is where the address is zero and not pointing to some location in memory.Nope. A null pointer is simply one that doesn't point to any value. Nothing in the spec says it's zero.
- A null reference is more or less the same thing (there are certain difference in the details).Nope. A null pointer and null reference in Java are the same thing.
- A null terminated string is one where null defines the end of the string.This does not exist in Java. As the above smartass pointed out, you can put the null character at the end of a String, but that character is part of the String, not a terminator.
>
If you are dealing with files and other types of I/O then this concept most certainly exists. Not in Java.
Just because you are limiting yourself to high-level use of Java, does not mean they aren't present in Java.The fact that null is precisely defined in the JLS and does not include these things means they aren't present in Java.

Converting bytes to unsigned bytes

      int u=0;
      int i=32;
byte [] data1 = new byte[1024];
int[] unsignedValue=new int[1024];
while(u<100){
                    unsignedValue[u] =data1[i] & 0xff;
                      u++;
                      i++;
                   } from input stream iam storing bytes in data1.now i want to convert specific bytes to unsigned bytes.
here i tryed in the above way but i want to convert
2 to 8
12 to 18
22 to 28
bytes to unsigned and i want to store how can i do this?

nanda_java wrote:
in my fist post only i multiplyes with 0xff .and i gave code ...my question is how to multiply only specific
2 to 8
12 to 18
22 to 28
bytes with 0xff .the bytes are in data1.I have no idea what you're saying, and I have no idea what the significance of those ranges is.
Look, you've already been told this twice: Say you get the byte 0xFE. That byte is neither signed nor unsigned. Get that into your head. It's simply a byte. The concept of signed/unsigned only comes into play when you decide to treat that as an integer value. You might want it to represent -2, or you might want it to represent 254. If you store it in a Java byte, it will represent -2. You cannot change that. If you want 0xFE to mean 254, then mask it with 0xFF and store it in an int.
byte b = -2;
System.out.println(b & 0xFF); // prints 254Furthermore, as already stated, in many cases it doesn't matter if it's signed or unsigned. If you do addtion, subtraction, multiplication (I think), AND, OR, XOR, you'll get the same byte result, regardless of whether you consider it signed or unsigned, and again, signed/unsigned only matters if you care about the numerical value of that signed result, rather than simply its bit pattern. 0xFE - 0x01 = 0xFD, and you can take that as -2 -1 = -3 or as 254 - 1 = 253. The bytes are the same regardless.
What part are you not understanding? Don't just keep repeating the same thing about how it's unsigned and 2 to 8 and all that nonsense.
So please, define your problem more clearly.
Edited by: jverd on Jan 10, 2008 8:53 AM

Form English Char ( Single Byte ) TO Double Byte ( Japanese Char )

Hello EveryOne !!!!
I need Help !!
I am new to Java ,.... I got assignment where i need to Check the String , if that string Contains Any Non Japanse Character ( a~z , A~Z , 0 -9 ) then this should be replaced with Double Byte ( Japanese Char )...
I am using Java 1.2 ..
Please guide me ...
thanks and regards
Maruti Chavan

hello ..
as you all asked Detail requirement here i an pasting C code where 'a' is passed as input character ..after process it is giving me Double Byte Japanese "A" .. i want this to be Done ..using this i am able to Convert APLHA-Numeric from singale byte to Doubel Byte ( Japanse ) ...
Same program i want to Java ... so pleas guide me ..
#include <stdio.h>
int main( int argc, char *argv[] )
char c[2];
char d[3];
strcpy( c, "a" ); // a is input char
d[0] = 0xa3;
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please ..
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Maruti Chavan

High bytes and low bytes?

What are high bytes and low bytes? Thanks for helping.

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Changing a byte in a byte array???? HELP

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