Question

I am using ByteBuffer APIs to convert an object into bytes. The object’s class is as follows

public class Obj{
int a; // size 1 byte
int b; // size 4 bytes
int c; // size 4 bytes
}

Using ByteBuffer API, I have allocated an object

ByteBuffer bbf = ByteBuffer.allocate(9);
bbf.put((byte) this.getA());
bbf.putInt(this.getB());
bbf.putInt(this.getC());
byte[] msg = bbf.array();

I set the value of B as 100 but when I convert the byte array from offset 1 till length 4, I get a different integer value.
Any idea where is the problem?
thanks!

Answer 1

The code works as it should, and if you indeed select bytes with index 1,2,3,4 they will yield the value 100:

ByteBuffer bbf = ByteBuffer.allocate(9);
bbf.put((byte) 10);
bbf.putInt(100);
bbf.putInt(55);
byte[] msg = bbf.array();

byte[] from4to8 = Arrays.copyOfRange(msg, 1, 5);

ByteBuffer buf2 = ByteBuffer.wrap(from4to8);
System.out.println(buf2.getInt());             // Prints 100

---

Some notes:

• Keep in mind that the endian may differ from system to system (so check the endian on both hosts if this is part of a protocol)

• The array you get from the bbf.array() call is a backing array, i.e.:

  Modifications to this buffer’s content will cause the returned array’s content to be modified, and vice versa.