Objects
Much of the power and flexibility of modern software analysis and design derives from its use of objects.
Classes
Classes create an abstract representation of the world, letting you discard unnecessary details.
The 3 properties
Class
properties
behavior
relationships to other objects
Object
state
behavior
identity
Ref: http://javadevwannabe.blogspot.sg/2012/02/state-behavior-and-identity.html?m=1