hex conversion methods

[dendenners]

Hi there,
I'm having trouble converting a 4 byte hex value into the correct int value that it represents. I was wondering would anyone know where I could find some generic method that takes in a byte array with numerical hex values and returns the calculated int value? Thanks
(e.g. if my 4 byte array contains byte[0]=00,byte[1]=00, byte[2]=01, byte[3]=4A, the correct value is A*1 + 4*16 + 1*256=10 + 64 + 256 = 330)

 

[pipk]

You may wish to check out deitel & deitel "Java How to program" edition 3 page 491.

They have a little swing applicatioon which converts between number bases by entering the number and the radix (i.e. hex is 16, binary is 2 blah blah blah).

You can use some of the static methods available within the java.lang package such as Character.digit(yourChar, radix);

which will convert a character to its numerical equivalent depending on the value of the radix you pass.

e.g (A , 16) will return the value of 10

you can check out their books (all code examples are downloadable from their website) at the following url, I couldn't find the third edition so you may have to download the code examples and look for the chapter on Strings and Characters (chapter 10) for the example I am looking at.

best of luck

http://www.deitel.com/books/downloads.html

 

[toolkit]

An example of what you are trying to achieve:

import java.io.ByteArrayInputStream;

public class IntStream extends ByteArrayInputStream {

  public IntStream( byte[] buf ) {
    super( buf );
  }

  public int readInt() {
    int result = 0;
    int current;
    for( int i = 0; i < 4; i++ ) {
      if( ( current = this.read() ) == -1 )
        return -1;
      result = result * 256 + current;
    }
    return result;
  }


  public static void main( String[] args ) {
    IntStream ints = new IntStream( new byte[] { 0x00, 0x00, 0x01, 0x4A } );
    int current;
    while( ( current = ints.readInt() ) != -1 )
      System.out.println( current );
  }
}

Sorry if I'm missing a more obvious conversion of real byte quartets to integers...
Cheers, Neil

 

[toolkit]

Or another way:

public class Convert {

  private Convert() {}

  public static int convert( byte[] buf ) {
    if( buf.length > 4 )
      throw new IllegalArgumentException( "array length must not exceed 4");

    return ( (int) buf[0] << 24 ) +
           ( (int) buf[1] << 16 ) +
           ( (int) buf[2] << 8  ) + 
           ( (int) buf[3] );
  }

  public static void main( String[] args ) {
    System.out.println( convert( new byte[] { 0x00, 0x00, 0x01, 0x4A } ) );
  }
}

 

[toolkit]

Figured out the best approach:

import java.io.DataInputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;

public class BestMethod {

  private BestMethod() {}

  public static int convert( byte[] buf )
    throws IOException
  {
    if( buf.length > 4 )
      throw new IllegalArgumentException( "array length must not exceed 4");

    DataInputStream dis = new DataInputStream( new ByteArrayInputStream( buf ) );

    return dis.readInt();
  }

  public static void main( String[] args ) {
    try {
      System.out.println( convert( new byte[] { 0x00, 0x00, 0x01, 0x4A } ) );
    } catch( IOException e ) {}
  }
}

Thanks for posting the question dendenners. Its helped me learn a bit more about the java.io package
Cheers, Neil