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CS1 Course Site
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Wait , WAIT !!What's that word ? ( Class Notes ( without definitions ) )
Monday September 13 , 2000
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Remark
As an activity to aquaint us with the creation and use of objects (i.e, scripts) we will solve a collection of problems posed in the context of a ``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 >
- This program creates a new circle who's radius is the given number.
- < circle > .radius () -- > < double >
- compute the radius of the given circle
- < circle > .diameter () -- > < double >
- compute the diameter of the circle.
- < circle > .area () -- > < double >
- compute the area of the circle
- < circle > .perimeter () -- > < double >
- compute the perimeter of the circle.
- < circle > .describe ()
- < circle > .expand (< double >)
- increases the radius of the circle by the given number.
- < circle > .shrink (< double >)
- decrease the radius of the circle by the given number.
Tasks
Suppose c and d have been bound to circles.
- Display the area of circle c.
IO.println (c.area ());
- 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;
- Expand circle d by adding 10 to its radius
d.expand (10.0);
- Display the area of a circle of radius 15.
Circle clara = new Circle (15);
double areaOfClara = clara.area ();
IO.println (areaOfClara);
Notes
Circle is a class
clara is an instance
IO is a class
15 is a ``primitive atomic type.''
area is an instance method.
println is a static method
Problem
A circular garden of diameter 58.2 meters is surrouned by a 2 meter brick walkway. What is the area of the walkway?
To solve this we will use Problem Decomposition.
The Java program
< CLASS > -- > WalkwayApp
< NEEDS > -- > import blue.shapes. *;
< PROGRAM > -- >
/ /record the given information
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 (radiusOfXGarden);
/ /compute the area of the walkway
double walkWayArea = xgarden.area () - garden.area ();
/ /display result
IO.print ( ``The area is: ``);
IO.print (walkWayArea);
Bindings
garden --- > o
xgarden -- > O
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