Object(instance): basic unit of object-oriented programming and represent real life entities.

Object(instance): basic unit of object-oriented programming and represent real life entities.

1. Field(optional): primitives or references to object.

   • Also can refer to another object

2. Method(optional): a class objects can do

   • Declaration part (the signature of the method)
     • Return value
       • or primitive
       • or object
       • or void: null
     • Mthod name
     • list of arguements
   • Body
     • code that perform the action
   • Main: a special method
     • Application : many class and only one need main method to be invoked
   • UML diagram: summary of all fields type and methods signature

3. Class: a blueprint or a template to create objects of identical type.Determine the object(name methods field)

   • ＞=1 Constructor
     • Like a method, but no return value, the same name with the class. the argument to initialize the field
   • allocate memory space for data that will be assigned to the vairable.
     • stack :pimitives
     • heap: JAVA object

4. Abstraction: the act of using programming object to represent a real-world object

5. ＞=1 reference variable

   • Null: no value .Test by operator