Chapter 9 : Polymorphism, Dynamic Typing, and Dynamic Binding

Object-Oriented Programming Language
Chapter 9 : Polymorphism, Dynamic Typing, and Dynamic Binding

Atit Patumvan
Faculty of Management and Information Sciences
Naresuan University

2

The Three Key Concepts

• Polymorphism: objects from different class can deﬁne
methods that share the same name

• Dynamic Typing: the determination of the class that an
object belongs to unit the program is executing.

• Dynamic Binding: the determination of the actual method to
invoke an object unit program execution time

Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language

3

Polymorphism: Same Name, Different Class

Program 9.1 main.m
01: #import "Complex.h"
02:
03: @implementation Complex
Complex
04:
05: @synthesize real, imaginary; real : double
06: imaginary : double
07: -(void) print
08: { print() : void
09:! NSLog (@" %g + %gi ", real, imaginary); setReal(double) : void andImaginary(double) : double
20: } add(Complex) : Complex
21:
22: -(void) setReal: (double) a andImaginary: (double) b
23: {
24:! real = a;
25:! imaginary = b;
26: }
27:
28: -(Complex *) add: (Complex *) f
29: {
30:! Complex *result = [[Complex alloc] init];
31:! result.real = real + f.real;
32:! result.imaginary = imaginary + f.imaginary;
33:! return result;
34: }
35: @end

4


Fraction Complex

int : numerator real : double
int : denominator imaginary : double

print() : void print() : void
setTo(int) over(int) : (void) setReal(double) : void andImaginary(double) : double
convertToNum : (double) add(Complex) : Complex
add(Fraction) : Fraction
reduce() : void
Program 9.1 Fraction.m
:
38: -(Fraction *) add: (Fraction * ) f
38: {
38:! Fraction * result = [[Fraction alloc] init];
38:! result.numerator = numerator * f.denominator + denominator * f.numerator;
38:! result.denominator = denominator * f.denominator;
38:! [result reduce];
38:
38:! return result;
38: }
:

5


Fraction Complex


setTo(int) over(int) : (void) setReal(double) andImaginary(double) : double
reduce() : void

Program 9.1 Complex.m
:
38: -(Complex *) add: (Complex *) f
38: {
38:! Complex *result = [[Complex alloc] init];
38:! result.real = real + f.real;
38:! result.imaginary = imaginary + f.imaginary;
38:! return result;
38: }
:

6


Program 9.1 main.m
:
09: Fraction *f1 = [[Fraction alloc] init]; Complex
10: !! Fraction *f2 = [[Fraction alloc] init];
11: !! Fraction *fracResult; real : double
12: !! Complex *c1 = [[Complex alloc] init]; imaginary : double
13: !! Complex *c2 = [[Complex alloc] init];
14: !! Complex *compResult; print() : void
15: ! setReal(double) : andImaginary(double) : double
16: !! [f1 setTo: 1 over: 10]; add(Complex) : Complex
17: !! [f2 setTo: 2 over: 15];
18: !
19: !! [c1 setReal: 18.0 andImaginary: 2.5]; Fraction
20: !! [c2 setReal: -5.0 andImaginary: 3.2];
: !
int : numerator
25: !! compResult = [c1 add: c2];
int : denominator
26: !! [compResult print];
: ! print() : void
36: !! fracResult = [f1 add: f2]; setTo(int) over(int) : (void)
37: !! [fracResult print]; convertToNum : (double)
: !! add(Fraction) : Fraction
reduce() : void


7

Dynamic Binding and the id Type

Program 9.2 main.m
:
09:! id dataValue;
10:! Fraction *f1 = [[Fraction alloc] init];
11:! Complex *c1 = [[Complex alloc] init];
12:
13:! [f1 setTo: 2 over: 5]; Fraction
14:! [c1 setReal: 10.0 andImaginary: 2.5];
15: int : numerator
16:! // first dataValue gets a fraction int : denominator
17:
18:! dataValue = f1; print() : void
19:! [dataValue print]; setTo(int) over(int) : (void)
20: convertToNum : (double)
21:! // now dataValue gets a complex number add(Fraction) : Fraction
22:! dataValue = c1; reduce() : void
22:! [dataValue print];
23:!
24:! [c1 release];
25:! [f1 release]; dataValue f1
:
numerator = 2
Fraction@yyyy
denominator = 5
id Fraction@yyyy


8

Dynamic Binding and the id Type

Fraction * f1 = [[Fraction alloc] init];
id f2 = f1;

f1

Fraction@yyyy

f2 Fraction

numerator = 2
Fraction@yyyy
denominator = 5
id
Fraction@yyyy


9

Argument and Return Types with Dynamic Typing

Fraction Complex


setTo(int) over(int) : (void) setReal(double) andImaginary(double) : double
reduce() : void

id add (id dataValue1, id dataValue2)
{
return [dataValue1 add: dataValue2];
}


10

Methods for Working with Dynamic Types

Method Question or Action

-(BOOL) isKindOfClass: class-object Is the object a member of class-object or a descendant?

-(BOOL) isMemberOfClass: class-object Is the object a member of class-object?

Can the object respond to the method specified by
-(BOOL) respondsToSelector:selector
selector?

+(BOOL) instancesRespondToSelector: selector Can instances of the specified class respond to selector?

+(BOOL)isSubclassOfClass: class-object Is the object a subclass of the specified class?

-(id) performSelector: selector Apply the method specified by selector

Apply the method specified by selector, passing the
-(id) performSelector: selector withObject: object
argument object.
-(id) performSelector: selector withObject: object1 Apply the method specified by selector with the
withObject: object2 arguments object1 and object2.

11

Exception Handling Using @try

Program 9.4 main.m
01: #import "Fraction.h"
02:
03: int main (int argc, char *argv [])
04: {
05: ! NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
06:! Fraction *f = [[Fraction alloc] init];
07:! [f noSuchMethod];
08:! NSLog (@"Execution continues!");
09:! [f release];
10:! [pool drain];
11:! return 0;
12: } $ ./main
2012-04-08 12:36:14.589 main[4336:707] -[Fraction noSuchMethod]: unrecognized selector sent to instance
0x10be0c210
2012-04-08 12:36:14.590 main[4336:707] *** Terminating app due to uncaught exception
'NSInvalidArgumentException', reason: '-[Fraction noSuchMethod]: unrecognized selector sent to instance
0x10be0c210'
*** First throw call stack:
(
! 0 CoreFoundation 0x00007fff91708fc6 __exceptionPreprocess + 198
! 1 libobjc.A.dylib 0x00007fff9344dd5e objc_exception_throw + 43
! 2 CoreFoundation 0x00007fff917952ae -[NSObject doesNotRecognizeSelector:] +
190
! 3 CoreFoundation 0x00007fff916f5e73 ___forwarding___ + 371
! 4 CoreFoundation 0x00007fff916f5c88 _CF_forwarding_prep_0 + 232
! 5 main 0x000000010bd37bf2 main + 194
! 6 main 0x000000010bd376d4 start + 52
)
terminate called throwing an exceptionAbort trap: 6


12

@try and @ catch Statement

@try {
statement throw exception
statement
... Exception

}
@catch (NSException *exception) { catch exception
statement
statement
...
}


13

Exception Handling Using @try

Program 9.5 main.m
01: #import "Fraction.h"
02:
03: int main (int argc, char *argv [])
04: {
05:! NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
06:! Fraction *f = [[Fraction alloc] init];
07:
08:! @try {
09:! ! [f noSuchMethod];
10:! }
11:! @catch (NSException *exception) {
12:! ! NSLog(@"Caught %@%@", [exception name], [exception reason]);
13:! }
14:! NSLog (@"Execution continues!");
15:! [f release];
16:! [pool drain];
17:! return 0;
18: }

$ ./main
2012-04-08 12:45:32.562 main[4445:707] -[Fraction noSuchMethod]: unrecognized selector sent to instance 0x10870c210
2012-04-08 12:45:32.564 main[4445:707] Caught NSInvalidArgumentException-[Fraction noSuchMethod]: unrecognized selector sent to
instance 0x10870c210
2012-04-08 12:45:32.564 main[4445:707] Execution continues!
$


Chapter 9 : Polymorphism, Dynamic Typing, and Dynamic Binding

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