Serialisation is where an object (or objects) is converted into a sequence of bits in order for it to be stored or transmitted. The bits can be unserialised at the other end to recreate the objects. Its actually quite a cool thing, and something very nice which Java provides (as do other languages, but its nice the way it is so built into Java.)
In order to override the default, your class can implement the Externalizable interface, there are two methods ( readExternal and writeExternal) which you will need to implement - have a look at java.sun.com/api
. Certainly in some aspects the Java serialisation isn't all that great, I know for some Java HPC applications (however few there are) the programmers used their own serialisation and obtained a significant boost in performance.