When you "Serialize" an object, you make a full description of it so that it can be restored later. In this description, all fields of the object are stored (Even private, protected and internal fields). With this description, you can regenerate the object later. You could compare it to the transporter in the Star Trek TV series. When you hear "Beam me up, Scotty!" the person on the far far away planet gets beamed up atom by atom and then rebuilt on the ship.