531/notes-simple-classes.txt
----------------------------

Classes -- defining and using them.

OOP - Object Oriented Programming

program:  objects of certain types (classes)
          send each other messages to tell them to carry out "methods" (procedures)
          main() method -- special case, to get program started.

objects = data + "methods" (procedures) you can ask them to carry out.

                                                    Examples:
Class      defines a *type* of object:              Car  Person  Ant  AntEater  Firm

Instance   specific instances of the class          One Ant instance for each "ant" 
           Each represents a particular "entity"        being modeled.
      
Fields     slots for storing data 
           Ex: Age  Height  MaxSpeed Weight 

  Instance variables (fields) -- slots in each instance      
     Because different objects in program represent different entities

  Class (static) variables (fields) -- slots in the Class object itself
     same value for all instances of the class.     MutationRate

To Define a Class:
   YourClassName    extends (subclass of) SomeClass 
   fields:  names, data types;  access control;    May be static;
   methods: names ( parameters) and what they do!   May be static
   constructors:  special methods invoked with "new" to create new instances

To use a class
   Define a "reference" variable to hold address of (pointer to) object
   Use "new" to create an instance, store in the ref. variable
   Send the instance messages to ask it to do things (ie execute methods).
   General form:   
              addressOfObject.methodName()
   Examples:
              double d = Math.cos(2.1);
              double r = rng.nextGuassian();
              o.setWeight( 2.2 );

See SimpleClass1.java program for examples of all the above operations.

Read in JavaTech (or elsewhere)
  Class Definition
  Data Fields; Methods; Constructors

Note:
  method signature: overloading
     public   void      setWeight ( double wt )
     ^^^^^^   ^^^^      ^^^^^^^^^   ^^^^^^^^^
     access   return    name        arguments (aka parameters)
            value type
 
  method body:  everything it does, between the { ... } after the signature
  variables available:
        static (class) fields
        instance fields
        local fields


------------------------------------------------------------------------
  



-------------------------------------------------------------------------
Abstract view of classes/methods:    (See the Chapter 3 Supplemental material)

Class as new type of data, e.g., like "int" but more complex!

   fields -- what data is stored           int -> store an integer

   methods -- like operators on the data: what can be done

 Thus define and use these new "building blocks" in your programs.

--------------------------------------------------------------------------