1 - (id) init 2 { 3     return [self initWithWidth: 0 andHeight: 0]; 4 } 5  6 - (id) initWithWidth: (int) w andHeight: (int) h 7 { 8     self = [super init]; 9     if (self) {10         [self setWidth: w andHeight: h];11     }12     return self;13 }

 1 - (id)init 2 { 3     return [self initWithSide:0]; 4 } 5  6 - (id) initWithSide: (int) side 7 { 8     self = [super init]; 9     if (self) {10         [self setSide:side];11     }12     return self;13 }

 1 //.m文件定义静态变量  增加类方法 2 #import "Fraction.h" 3  4 static int gCounter; 5  6 @implementation Fraction 7 @synthesize numerator, denominator; 8  9 10 - (Fraction *) add: (Fraction *) f11 {12     Fraction *result = [[Fraction alloc] init];13     14    result.numerator = numerator * f.denominator + denominator * f.numerator;15    result.denominator = denominator * f.denominator;16     17     [result reduce];18     gCounter++;19     return result;20 }21 22 + (int) count23 {24     return gCounter;25 }

 1         typedef Fraction * FractionObj; 2          3         FractionObj f1 = [[Fraction alloc] init], 4                     f2 = [[Fraction alloc] init]; 5          6         [f1 setTo: 1 over: 2]; 7         [f2 setTo: 2 over: 3]; 8          9         [f1 print];10         [f2 print];