多态性(Polymorphism)

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2023-12-01

polymorphism这个词意味着有许多形式。 通常,当存在类的层次结构并且它们通过继承相关时,会发生多态性。

Objective-C多态意味着对成员函数的调用将导致执行不同的函数,具体取决于调用该函数的对象的类型。

考虑一下这个例子,我们有一个类Shape,它为所有形状提供基本接口。 Square和Rectangle派生自基类Shape。

我们有方法printArea来展示OOP特征polymorphism

#import <Foundation/Foundation.h>
@interface Shape : NSObject {
   CGFloat area;
}
- (void)printArea;
- (void)calculateArea;
@end
@implementation Shape
- (void)printArea {
   NSLog(@"The area is %f", area);
}
- (void)calculateArea {
}
@end
@interface Square : Shape {
   CGFloat length;
}
- (id)initWithSide:(CGFloat)side;
- (void)calculateArea;
@end
@implementation Square
- (id)initWithSide:(CGFloat)side {
   length = side;
   return self;
}
- (void)calculateArea {
   area = length * length;
}
- (void)printArea {
   NSLog(@"The area of square is %f", area);
}
@end
@interface Rectangle : Shape {
   CGFloat length;
   CGFloat breadth;
}
- (id)initWithLength:(CGFloat)rLength andBreadth:(CGFloat)rBreadth;
@end
@implementation Rectangle
- (id)initWithLength:(CGFloat)rLength andBreadth:(CGFloat)rBreadth {
   length = rLength;
   breadth = rBreadth;
   return self;
}
- (void)calculateArea {
   area = length * breadth;
}
@end
int main(int argc, const char * argv[]) {
   NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
   Shape *square = [[Square alloc]initWithSide:10.0];
   [square calculateArea];
   [square printArea];
   Shape *rect = [[Rectangle alloc]
   initWithLength:10.0 andBreadth:5.0];
   [rect calculateArea];
   [rect printArea];        
   [pool drain];
   return 0;
}

编译并执行上述代码时,会产生以下结果 -

2013-09-22 21:21:50.785 Polymorphism[358:303] The area of square is 100.000000
2013-09-22 21:21:50.786 Polymorphism[358:303] The area is 50.000000

在上面的示例中,基于calculateArea和printArea方法的可用性,无论是基类中的方法还是执行派生类。

多态性基于两个类的方法实现来处理基类和派生类之间的方法切换。