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CS1 at Oswego

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My Intro to Object-Oriented Programming  
 
 
 
Class Notes
Wednesday September 20 , 2000
 
Discussion continued in the ``Shapes World'' with the introduction of the Square Class.
  • Constructor:   new Square (< double >) -- > < Square >,  creates a square using a given side length
The operators for the Square Class include:
  • < Square > .side () -- > < double >,  computes the side length of the square
  • < Square > .area () -- > < double >,  computes the area of the square
  • < Square > .perimeter () -- > < double >,  computes the perimeter of the square
  • < Square > .diagonal () -- > < double >,  computes the diagonal of the square
Commands for the Square Class include:
  • < Square > .describe (),  describes the square
  • < Square > .expand (< double >),  increases the side length of the square by the given number
  • < Square > .shrink (< double >),  decreases the side length of the square by the given number
Using the Square Class,  CG then demonstrated their use by coding this interesting Java examples.

The design of a square flag is as follows:
  • the background is blue
  • the middleground is a white disk of maximal size,  minus the foreground
  • the foreground is a blue square which inscribes the disk
If the flag measures 3 feet on one side,  what is the blue area of the flag?
class BlueAndWhiteFlagApp 

import blue.shapes.   *; 

/ /Model the flag. 

double flagSide = 3.0;
Square flag = new Square (flagSide); 

/ /Model the disk. 

double diskDiameter = flagSide;
double diskRadius = flagSide / 2.0;
Circle disk = new Circle (diskRadius); 

/ /Model the interior square. 

double helperSquareSide = flagSide / 2.0;
Square helper = new Square (helperSquareSide);
double smallSquareSide = helper.diagonal ();
Square smallSquare = new Square (smallSquareSide); 

/ /Compute the blue area. 

double blueArea = flag.area () - disk.area () + smallSquare.area (); 

/ /Display result. 

IO.println (``The blue area is ``+ blueArea + ``square units.''); 

 

The concept of Imaginative Construction was presented.  

CG ended the lecture with a quick introduction to the Triangle Class.   Because of the nature of triangles,  three different constructors were presented:

  • new Triangle (< double >) -- > < Triangle >,  produces a triangle for all sides of equal length
  • new Triangle (< double >,  < double >) -- > < Triangle >,  the first number represents the length of two of the sides of the triangle
  • new Triangle (< double >,  < double >,  < double >) -- > < Triangle >,  use this operator if all the sides are of different length