I have this small code :
public static void main(String[] args) {
byte[] bytesArray = {7,34};
BigInteger bytesTointeger= new BigInteger(bytesArray);
System.out.println(bytesTointeger);
}
Output:1826
My question is what just happened how an array of bytes {7,34} converted into this number 1826 , what is the operation that caused this result ? like how to convert it manually
The number 1826 is, in binary, 11100100010.
If you split that in groups of 8 bits, you get the following:
00000111 00100010
Which are the numbers 7 and 34
7 and 34 is converted to binary and give 00000111 and 00100010.After join it becomes 11100100010 which is in decimal 1826.
As said, this creates a BigDecimal from its byte representation in big-endian order.
If we used long to store result, manual conversion may look like the following:
long bytesToLong(byte[] bs) {
long res = 0;
for (byte b : bs) {
res <<= 8; // make room for next byte
res |= b; // append next byte
}
return res;
}
E. g.:
byte[] bs;
bs = new byte[]{ 7, 34 };
assertEquals(new BigInteger(bs).longValue(), bytesToLong(bs)); // 1826
bs = new byte[]{ -1 };
assertEquals(new BigInteger(bs).longValue(), bytesToLong(bs)); // -1
