?
Solved

convert int(short or long) to byte array

Posted on 2002-03-04
8
Medium Priority
?
79,075 Views
Last Modified: 2011-08-18
I intend to convert a integer (or short or long) that is greater than a byte can hold (eg, 1111) to a byte array, since casting is simply cannot be used here, any other way can do it without lose precise? I have tried to use Integer wrapper class and use its toBinaryString() to convert the int to a string representation, eg 5->"101", then I really cannot find a way of converting "101" to a byte array with correct binary representation. Please help
0
Comment
Question by:gordon_guan
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
8 Comments
 
LVL 9

Expert Comment

by:Venci75
ID: 6839117
try this:
"101".getBytes();
0
 
LVL 9

Expert Comment

by:Venci75
ID: 6839172
String str = Integer.toBinaryString(12345);
byte[] byte_array = str.getBytes();
0
 
LVL 7

Accepted Solution

by:
Igor Bazarny earned 60 total points
ID: 6839424
Hi,

Try this:

int value = 0xcafebabe;
byte[] bytes = new byte[4];

for( int i=0; i<bytes.length; ++i ){
    int offset = (bytes.length-i-1)*8;
    bytes[i] = (value & (0xff << offset)) >>> offset;
}

for( int i=0; i<bytes.length; ++i ){
    System.out.print(Integer.toHexString(bytes[i])+" ");
}
System.out.println();

Regards,
Igor Bazarny,
Brainbench MVP for Java 1
www.brainbench.com
0
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

Author Comment

by:gordon_guan
ID: 6841193
hello vinci, I would say your answer is not the thing that I want and in my case, it is wrong. I would rather prefer bazany's answer since what he/she does is more or less the same as what I did. So please change the answer back. Thanks.
0
 

Author Comment

by:gordon_guan
ID: 6841194
hello vinci, I would say your answer is not the thing that I want and in my case, it is wrong. I would rather prefer bazany's answer since what he/she does is more or less the same as what I did. So please change the answer back. Thanks.
0
 
LVL 4

Expert Comment

by:m_onkey_boy
ID: 6842116
Here's another way:

private byte[] getBytes(int n) {
     BigInteger big = new BigInteger(Integer.toString(n));
     return big.toByteArray();
}
0
 
LVL 2

Expert Comment

by:UniDyne
ID: 9337726
Assuming v is the value of the integer you are trying to convert to bytes, try this:


byte b[] = new byte[4];
int i, shift;
            
for(i = 0, shift = 24; i < 4; i++, shift -= 8)
b[i] = (byte)(0xFF & (v >> shift));
0
 

Expert Comment

by:PingBannon
ID: 13517210
This is a more readable (and faster) solution than unidyne's.

I've also included the code to recreate the int from the byte array.  This is a fragment of a class I wrote called ByteArrayUtils; if anyone can give me a faster solution, I'd be very grateful!

Enjoy!

public static final int   NUMBER_OF_BITS_IN_A_BYTE = 8;
public static final short MASK_TO_BYTE             = 0xFF;
public static final int   SIZE_OF_AN_INT_IN_BYTES  = 4;


public static void writeInt( byte[] p_dest,  // not allocated and returned so array can be reused
                             int    p_toWrite )
{
    assert( p_dest.length >= SIZE_OF_AN_INT_IN_BYTES )
          : "Programming error: p_dest is too short to hold an int";
   
    // unrolled loop of 4 iterations
    p_dest[0] = p_toWrite & MASK_TO_BYTE );
    p_toWrite >>= NUMBER_OF_BITS_IN_A_BYTE;

    p_dest[1] = p_toWrite & MASK_TO_BYTE );
    p_toWrite >>= NUMBER_OF_BITS_IN_A_BYTE;

    p_dest[2] = p_toWrite & MASK_TO_BYTE );
    p_toWrite >>= NUMBER_OF_BITS_IN_A_BYTE;

    p_dest[3] = p_toWrite & MASK_TO_BYTE );
}

   
public static int readInt( byte[] p_src ) // must be of size 4
{
    assert( p_src.length >= SIZE_OF_AN_INT_IN_BYTES )
          : "Programming error: p_src is too short to hold an int";

    // unrolled loop of 4 iterations
    int result = (   p_src[ 0 ] & MASK_TO_BYTE );
    result    |= ( ( p_src[ 1 ] & MASK_TO_BYTE ) << 8 );
    result    |= ( ( p_src[ 2 ] & MASK_TO_BYTE ) << 16 );
    result    |= ( ( p_src[ 3 ] & MASK_TO_BYTE ) << 24 );

    return result;
}
0

Featured Post

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

After being asked a question last year, I went into one of my moods where I did some research and code just for the fun and learning of it all.  Subsequently, from this journey, I put together this article on "Range Searching Using Visual Basic.NET …
In this post we will learn how to connect and configure Android Device (Smartphone etc.) with Android Studio. After that we will run a simple Hello World Program.
Video by: Michael
Viewers learn about how to reduce the potential repetitiveness of coding in main by developing methods to perform specific tasks for their program. Additionally, objects are introduced for the purpose of learning how to call methods in Java. Define …
Viewers will learn about arithmetic and Boolean expressions in Java and the logical operators used to create Boolean expressions. We will cover the symbols used for arithmetic expressions and define each logical operator and how to use them in Boole…
Suggested Courses
Course of the Month9 days, 2 hours left to enroll

764 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question