声明父类Animal继承自NSObject

Animal.h

#ifndef oc_Animal_h
#define oc_Animal_h
@interface Animal : NSObject {
    @public
    int weight;
}
- (void)eat;

//重写默认构造方法
- (id) init;
//自定义构造方法
- (id) initWithWeight:(int)newWeight;

@end

#endif

#import <Foundation/Foundation.h>
#import "Animal.h"

@implementation Animal

- (void)eat {
    NSLog(@"体重：%d", weight);
}

//id 是万能指针，可指向任何对象, 不要再加上*
//重写默认构造方法init  构造方法:初始化对象
- (id) init
{
    if (self = [super init]) { //!=nil   先初始化父对象，再赋给self， 再初始化自有成员， 最后return self
        weight = 20;
    }
    return self;
}

//自定义构造方法
- (id) initWithWeight:(int)newWeight
{
    if (self = [super init]) {
        self->weight = newWeight;
    }
    return self;
}
@end

Dog.h

#ifndef oc_Dog_h
#define oc_Dog_h
#import "Animal.h"
@interface Dog : Animal {
    @public
    int speed;
}

@property int speed; //自动声明 get set方法

- (void)run;

//id 是万能指针，可指向任何对象, 不要再加上*
//重写init  构造方法:初始化对象
- (id) init; //重写 NSObject的init

- (id) initWithWeightSpeed:(int)newWeight:(int)newSpeed;

- (NSString*)description; //对象描述   //重写 NSObject的description
+ (NSString*)description; //类对象描述


@end

#endif

Dog.m

#import <Foundation/Foundation.h>
#import "Dog.h"

@implementation Dog

@synthesize speed; //编译器自动生成get、set的实现方法

- (void)run {
    NSLog(@"跑-速度：%d", speed);
}

//id 是万能指针，可指向任何对象, 不要再加上*
//重写init  构造方法:初始化对象
- (id) init
{
    if (self = [super init]) { //!=nil
        speed = 15;
        //self->speed = 15;
    }
    return self;
}

//自定义构造方法，调用父类自定义构造
- (id) initWithWeightSpeed:(int)newWeight:(int)newSpeed
{
    if (self = [super initWithWeight:newWeight]) {
        speed = newSpeed;
    }
    return self;
}
- (NSString*)description //对象描述   //重写 NSObject的description
{
    return [NSString stringWithFormat:@"weight=%d,speed=%d", weight, speed];
}
+ (NSString*)description //类对象描述
{
    return [NSString stringWithUTF8String:"<Dog : Animal>"];
}

@end

#import "Animal.h"
#import "Dog.h"
int main()
{
        Animal* animal = [[Animal alloc] init]; //默认构造
        [animal eat];
        animal = [[Animal alloc] initWithWeight:17]; //自定义构造
        [animal eat];
        
        Dog* adog = [[Dog alloc] init];//默认构造
        [adog run];
        [adog eat];
        adog = [[Dog alloc] initWithWeight:16];//父类的自定义构造
        [adog eat];
        adog = [[Dog alloc] initWithWeightSpeed:16:13];//Dog自身的 自定义构造
        [adog run];
        [adog eat];

        //多态创建对象
        Animal* xdog = [[Dog alloc] initWithWeightSpeed:33 :55];
        [xdog eat];
        Dog* mdog = xdog;
        [mdog run];
        
        //description方法调用
        NSLog([mdog description]); //调用对象方法
        NSLog(@"%@", mdog);//输出对象%@  默认调用description对象方法
        NSLog([Dog description]); //调用类方法
        NSLog([[Dog class] description]); //默认调用 description类方法  这里省略了@"%@"的format       

        return 0;
}

OC语言学习 (六) 继承、多态，构造方法，description方法