Hi Amol, everything in Java is an object except primitives data types. So primitives are not objects! There are 8 types of primitives data types in Java. The are defined by the language specification, that is, you cannot add/create your own primitives data type (while, you can create new objects) Data types are used to represents numbers (both integers and floating point), chars (which internally are treated as numbers) and boolean (true - false). I think you'll find really useful this link: http://java.sun.com/docs/books/tutorial/java/nutsandbolts/datatypes.html
primitives are basically sequence of bytes and non premitive are object references.While serializing also the premitives data types are copied to the stream byte by byte.Unlike C or C++ the size for all the premitives are fixed for all JVM's.