convert byte array block to DWORD (int) Java

Question

How can I convert byte array block of 4 to integer number.

If we had these bytes of file in Hex Editor:

CB 01 00 00

The hexidecimal value of this block is DWORD of 000001CB = 1CBhex = 459 in decimal.

How can I convert any byte array (byte[]) block (of four bytes) to integer (decimal value of block)?

I am looking for method like this:

public int getDecimalFromBlock( byte... bytes ) {
      for ( byte b: bytes ) {
          // do the magic
      }
}

Where parameter byte in number between byte range (-127, 127).

Answer 1

Let's assume that your byte order is Little Endian (based on your post), and so the decoding will be

int value = ((data[0]&0xff) |
    ((data[1]&0xff)<<8) |
    ((data[2]&0xff)<<16) |
    ((data[3]&0xff)<<24));

If the order is Big endian, it will look something like:

int value = ((data[3]&0xff) |
    ((data[2]&0xff)<<8) |
    ((data[1]&0xff)<<16) |
    ((data[0]&0xff)<<24));

In both cases the variant "data" is a "byte[]"

byte[] data = new byte[] {(byte)0xcb, 0x01, 0x00, 0x00};

Update to the edited request.

I assume you may have problems with 0xcb as interpreted as negative value, this may be fixed by applying a & operator

Complete code with test case

public class DecimalTest
{
    public static int getDecimalFromBlock( byte... bytes ) {
        int result = 0;
        for(int i=0; i<bytes.length; i++)
        {
            result = result | (bytes[i] & 0xff)<<(i*8);
        }
        return result;
    }

    public static void main(String[] args) throws IOException
    {
        System.out.println(getDecimalFromBlock(new byte[]{(byte)0xcb}));
        System.out.println(getDecimalFromBlock(new byte[]{(byte)0xcb, 0x01}));
        System.out.println(getDecimalFromBlock(new byte[]{(byte)0xcb, 0x01, 0x00}));
        System.out.println(getDecimalFromBlock(new byte[]{(byte)0xcb, 0x01, 0x00, 0x00}));
        System.out.println(getDecimalFromBlock(new byte[]{(byte)0xcb, 0x01, 0x00, 0x00, 0x00}));
    }
}