December
1998 QUESTION 5 Total Marks: 20 Marks |
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| In this question, you are to write a program to update a computer display. | ||
| (a) | Explain, stating one advantage, the
term inheritance in object-oriented programming.
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[3] |
| (b) | A geometric point consists of an x- and
y-coordinate. Define a class Point that contains: (1) two private integers to record the
coordinates; (2) a constructor that takes two integers and assigns the first to the
x-coordinate and the second to the y-coordinate; and (3) accessor functions for the
two coordinates.
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[5] |
| (c) | A pixel is a point that has
an associated colour, represented as an integer. Use inheritance to define a class Pixel
that includes: (1) an accessor method for the colour; (2) a method set_colour that takes a colour c, and sets the
pixel's colour to c.
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[4] |
| (d) | A computer screen is a 480 x 768
matrix of Pixels, defined by the class below. class
Screen {
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| (i) A pixel is on if its
colour is not 0. Write a function pixel_on that takes a point, and returns 1 if the pixel at that point is set or 0
otherwise.
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[3] | |
| (ii) Suppose we have two points p1 = (x1, y1) and p2 = (x2,y2), where x1 < x2 and y1 < y2, that form the lower-left and upper-right corners of a rectangle on
the screen. Write a method fill that takes two point p1 and p2 and a colour c, and sets the colour of every pixel in the rectangle described by p1 and p2 to c. State any assumptions you make. |
[5] | |