Also talked about were additional tags for Hypertexh including lists,  ordered and unordered.  

Definition   CLASSIFICATION is the process of grouping objects having like properties (structural and behavior) into sets.

Definition   A set of objects grouped together as a result of classification is called a CLASS .

Definition   An individual element of a class is referred to as an INSTANCE of the class.

Definition   An OBJECT,  in the abstract,  is a collection of ``parts'',  ``behaviors'',  and ``relations''.

Definition   For practical programming purposes,  an OBJECT is either a class or an instance of a class.

Definition   A class is sometimes referred to as a STATIC OBJECT .

Definition   An instance of a class is sometimes referred to as a DYNAMIC OBJECT .

REMARK
As an activity to aquaint us with the creation and use of objects (i.e.   scripting) we will solve a collection of problems posed in the context of a ``shapes world''.
``Shapes World'' - a conceptual entity consisting of circles,  squares,  rectangles,  triangles,  and polygons.   - A realm in which interesting computations on shapes abound.  

The Circle class
We will model a circle in terms of one number;  its radius and the following programs:
- > new Circle (< double >) - > < circle > (new instance)

• This program is used to create a new circle whose radius is the given number.
  

- > new < circle > .radius () - > < double >

• Compute the radius of the given circle.
  

- > new < circle > .diameter () - > < double >

• Compute the diameter of the given circle.
  

- > new < circle > .area () - > < double >

• Compute the area of the given circle.
  

- > new < circle > .perimeter () - > < double >

• Compute the perimeter of the given circle.
  

- > new < circle > .describe () - > < double >

• Describes the circle.
  

- > new < circle > .expand (double)

• Increases the radius of the circle by the given number.
  

- > new < circle > .shrink (double)

• Decrease the radius of the circle by the given number.
  

Tasks
Suppose c and d have been bound to cirlces. 

1) Display the area of circle c.
IO.println (c.area ());  

2) Declare a variable called avg and bind it to the average value of the radii of the two circles.
double avg = (c.radius () + d.radius ()) / 2.0;  

3) Expand circle d by adding 10 to it's radius
d.expand (10);  

4) Display the area of a circle of radius 15.

/ /create instance of circle   Circle clara = new Circle (15);   double areaOfClara = areaOfClara.area ();   IO.println (areaOfClara);

 

Notes
Circle is a class.
Clara is an instance of class Circle.
IO is a class.
15 is a ``primitive atomic type'' - can't send a message to it.  

Area is an instance method - associated w /clara.
Println is a static method - associated w /class so it's static.  

Problem
A circular garden of diameter 58.2 meters is surrounded by a 2 meter brick walkway.   What is the area of the walkway?
 

To solve this we will use Problem Decomposition.

- > WalkwayApp   - > import blue.shapes.   *;   - >     / /Record the given info   double diameterOfGarden = 58.2;   double walkwayWidth = 2.0;     / /Create the garden   double radiusOfGarden = (diameterOfGarden / 2.0);   Circle garden = new Circle (radiusOfGarden) ;      / /Create the ``extended garden''    double radiusOfXGarden = (radiusOfGarden + walkwayWidth);    Circle xGarden = new Circle (radius of xGarden);      / /Compute the area of the walkway    double WalkwayArea = xGarden.area () - garden.area ();      / /Display the result    IO.print ( ``The area is:   ``);    IO.println (walkwayArea);