The Xperia XZ isn’t made of a single piece of machined aluminium like an iPhone, though. Its back panel is one piece, while the sides are another. There are even a few plastic panels too. They cover the top and bottom edges, and the little strip towards the bottom of the back.
Sony has styled out this seam-heavy design perfectly, though. There are no sharp edges to ruin the feel, and all the parts are perfectly colour-matched.