Comment
I found the concepts in this chapter relatively straight forward. However the later exercises for this chapter appear to be quite challenging but hopefully they aren't that hard.
EDIT: The formatting of several areas of this post, didn't exactly turn out the way I'd hoped hopefully it doesn't make it too difficult to read.
Exercises
1. Add a new class called ClassC, which is a subclass of ClassB, to Program 8.1. Make an initVar method that sets the value of its instance variable x to 300. Write a test routine that declares ClassA, ClassB, ClassC objects and invokes their corresponding initVar methods.
ANS - Copy and Paste of code and its console output
#import
//ClassA
@interface ClassA: NSObject
{
int x;
}
-(void) initVar;
-(void) printVar;
@end
@implementation ClassA
-(void) initVar
{
x = 100;
}
-(void) printVar
{
NSLog(@"x = %i", x);
}
@end
//ClassB
@interface ClassB : ClassA
-(void) initVar;
@end
@implementation ClassB
-(void) initVar
{
x = 200;
}
@end
//ClassC
@interface ClassC : ClassB
-(void) initVar;
@end
@implementation ClassC
-(void) initVar
{
x = 300;
}
@end
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
ClassA *a = [[ClassA alloc] init];
ClassB *b = [[ClassB alloc] init];
ClassC *c = [[ClassC alloc] init];
[a initVar];
[b initVar];
[c initVar];
[a printVar];
[b printVar];
[c printVar];
[a release];
[b release];
[c release];
[pool drain];
return 0;
}
[Session started at 2009-06-03 09:33:32 +0100.]
2009-06-03 09:33:32.788 Chap8_Ex1[282:10b] x = 100
2009-06-03 09:33:32.790 Chap8_Ex1[282:10b] x = 200
2009-06-03 09:33:32.790 Chap8_Ex1[282:10b] x = 300
The Debugger has exited with status 0.
2. When dealing with higher-resolition devices, you might need to use a coordinate system that enables you to specify points as floating-point values instead of as simple integers. Modify the XYPoint and Recatangle classes from this chapter to deal with floating-point numbers. The rectangle's width, height, area, and perimeter should all work with floating-point numbers as well.
ANS - Code for modified Rectangle and XYPoint header and implementation files
//
// Rectangle.h
// Ex2
//
// Created by Waqas Arshid on 03/06/2009.
// Copyright 2009 __MyCompanyName__. All rights reserved.
//
#import
@class XYPoint
@interface Rectangle : NSObject
{
float width;
float height;
XYPoint *origin;
}
@property float width, height;
-(XYPoint *) origin;
-(void) setOrigin: (XYPoint *) pt;
-(void) setWidth: (float) w andHeight: (float) h;
-(float) area;
-(float) perimeter;
@end
//
// Rectangle.m
// Ex2
//
// Created by Waqas Arshid on 03/06/2009.
// Copyright 2009 __MyCompanyName__. All rights reserved.
//
#import "Rectangle.h"
#import "XYPoint.h"
@implementation Rectangle
@synthesize width, height;
-(void) setWidth: (float) w andHeight: (float) h
{
width = w;
height = h;
}
-(float) width
{
return width * height;
}
-(float) perimeter
{
return (width + height) * 2;
}
-(void) setOrigin: (XYPoint *) pt
{
origin = pt;
}
-(XYPoint *) origin
{
return origin;
}
@end
//
// XYPoint.h
// Ex2
//
// Created by Waqas Arshid on 03/06/2009.
// Copyright 2009 __MyCompanyName__. All rights reserved.
//
#import
@interface XYPoint : NSObject
{
float x;
float y;
}
@property float x, y;
-(void) setX: (float) xVal andY: (float) yVal;
@end
//
// XYPoint.m
// Ex2
//
// Created by Waqas Arshid on 03/06/2009.
// Copyright 2009 __MyCompanyName__. All rights reserved.
//
#import "XYPoint.h"
@implementation XYPoint
@synthesize x, y;
-(void) setX: (float) xVal andY: (float) yVal
{
x = xVal;
y = yVal;
}
@end
3. Modify the Program 8.1 to add a new class called ClassB2 that, like ClassB, is a subclass of ClassA.
What can you say about the relationship between ClassB and ClassB2?
Identify the hierarchical relationship between the Object class, ClassA, ClassB and ClassB2.
What is the superclass of ClassB?
What is the superclass of ClassB2?
How many subclasses can a class have, and how many superclasses can it have?
ANS - ClassB and ClassB2 are sibling classes, they both share the same parent class.
Object
|
|
|
ClassA
| |
| |
| |
ClassB ClassB2
|
|
|
ClassC
The superclass of ClassB is ClassA
The superclass of ClassB2 is ClassA
A class can have an infinite number of subclasses.
A class can only have one superclass.
4. Write a Rectangle method called translate: that takes a vector called XYPoint (Xv, Yv) as its argument. Have it translate the rectangle's origin by the specified vector.
ANS - I don't understand this question. Is it intending on distinguishing the origin of a rectangle from a co-ordinate on the rectangle and existing parameters such as width and height?
5. Define a new class called GraphicObject, and make it a subclass of NSObject. Define instance variables in your new class as follows:
int fillColour; // 32-bit colour
BOOL filled; // Is the object filled?
int lineColour; // 32-bit line colour?
Write methods to set and retrieve the variables defined previously.
Make the Rectangle class a subclass of GraphicObject
Define new classes, Circle and Triangle, which are also subclasses of GraphicObject. Write methods to set and retrieve the various parameters for these objects and also to calculate the the circle's circumference and area, and the triangle's perimeter and area.
ANS - Copy and Paste of all interface/implementation with a main program and console output to test the new classes and methods
#import
//GraphicObject
@interface GraphicObject : NSObject
{
int fillColour;
BOOL filled;
int lineColour;
}
@property int fillColour, lineColour;
-(void) setFilled;
-(BOOL) filled;
@end
@implementation GraphicObject
@synthesize fillColour, lineColour;
-(void) setFilled
{
filled = TRUE;
}
-(BOOL) filled;
{
return filled;
}
@end
//Rectangle
@interface Rectangle : GraphicObject
{
int width;
int height;
}
@property int width, height;
-(void) setWidth: (int) w andHeight: (int) h;
@end
@implementation Rectangle
@synthesize width, height;
-(void) setWidth: (int) w andHeight: (int) h
{
width = w;
height = h;
}
@end
//Circle
@interface Circle : GraphicObject
{
int radius;
}
@property int radius;
-(float) circumference;
-(float) area;
@end
@implementation Circle
@synthesize radius;
-(float) circumference
{
return 2 * 3.14 * radius; // circumference equals '2 pi r'
}
-(float) area
{
return 3.14 * ( radius * radius ); //area equals 'pi r squared'
}
@end
//Triangle
@interface Triangle : GraphicObject
{
int base;
int height;
float perpHeight;
}
@property int base, height;
@property float perpHeight;
-(int) perimeter;
-(float) area;
-(void) setBase: (int) b andHeight: (int) h;
@end
@implementation Triangle
@synthesize base, height;
@synthesize perpHeight;
-(int) perimeter
{
return base + height + height;
}
-(float) area
{
perpHeight = ( height / 2 ) * 3;
return 0.5 * base * perpHeight;
}
-(void) setBase: (int) b andHeight: (int) h
{
base = b;
height = h;
}
@end
//main
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
Rectangle *aRectangle = [[Rectangle alloc] init];
Triangle *aTriangle = [[Triangle alloc] init];
Circle *aCircle = [[Circle alloc] init];
[aRectangle setWidth: 5 andHeight: 3];
[aTriangle setBase: 5 andHeight: 3];
[aCircle setRadius: 5];
NSLog (@"Rectangle width is: %i height is: %i", aRectangle.width, aRectangle.height);
NSLog (@"Triangle base is: %i height is: %i", aTriangle.base, aTriangle.height);
NSLog (@"Circle radius is: %i", aCircle.radius);
NSLog (@"Circle circumference is: %f area is: %f", aCircle.circumference, aCircle.area);
NSLog (@"Triangle perimeter is: %i area is: %f", aTriangle.perimeter, aTriangle.area);
[aRectangle release];
[aTriangle release];
[aCircle release];
[pool drain];
return 0;
}
[Session started at 2009-06-12 00:52:52 +0100.]
2009-06-12 00:52:52.629 Ex5[258:10b] Rectangle width is: 5 height is: 3
2009-06-12 00:52:52.631 Ex5[258:10b] Triangle base is: 5 height is: 3
2009-06-12 00:52:52.631 Ex5[258:10b] Circle radius is: 5
2009-06-12 00:52:52.632 Ex5[258:10b] Circle circumference is: 31.400000 area is: 78.500000
2009-06-12 00:52:52.632 Ex5[258:10b] Triangle perimeter is: 11 area is: 7.500000
The Debugger has exited with status 0.
6. Write a Rectangle method called intersect: that takes a rectangle as an argument and returns a rectangle representing the overlapping area between the two rectangles. For example, given two rectangles of dimensions (250 width x 75 height) and (100 width x 180 height), the method should return a rectangle whose origin is at (400, 420), whose width is 50, and whose height is 60.
If the rectangles do not intersect, return one whose width and height are zero and whose origin is at (0, 0).
ANS - @d. I couldn't work this one out completely without a few complications, will bring in code.
7. Write a method for the Rectangle class called draw that draws a rectangle using dashes and vertical bar characters. The following code sequence
Rectangle *myRect = [[Rectangle alloc] init];
[myRect setWidth: 10 and Height: 3];
[myRect draw];
[myRect release];
would produce the following output:
_____
| |
| |
| |
_____
ANS - Copy and Paste of new method and test program with console output. I couldn't get this to work either. Will bring it in also. @d. This is the modified version of the method draw from what you told me about assigning the number of lines/spaces to a string variable and displaying it at the end. However this didn't seem to work also, I am unsure as to why that is.
-(void) draw
{
int n, count;
char space, line;
for ( n = 1; n <= width; ++n ) {
line += "_";
}
NSLog (@"%c", line);
n = 0;
for ( n = 1; n <= height; ++n ) {
NSLog (@"|");
for ( count = 1; n <= (width - 2); ++count ) {
space += " ";
}
NSLog (@"%c", space);
NSLog (@"|");
}
n = 0;
for ( int n = 1; n <= width; ++n ) {
NSLog (@"_");
}
}
No comments:
Post a Comment