Convert a byte array to integer in Java and vice versa

Use the classes found in the java.nio namespace, in particular, the ByteBuffer. It can do all the work for you.

byte[] arr = { 0x00, 0x01 };
ByteBuffer wrapped = ByteBuffer.wrap(arr); // big-endian by default
short num = wrapped.getShort(); // 1

ByteBuffer dbuf = ByteBuffer.allocate(2);
dbuf.putShort(num);
byte[] bytes = dbuf.array(); // { 0, 1 }