oc-18-继承

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

@interface Animal : NSObject
{
int _age; // 不写@public，默认只能在本类和子类当中访问.间接继承.
}
@end

//Animal.m
#import "Animal.h"
@implementation Animal
{
int _weight; // 写在.m文件中的成员变量,叫做私有成员变量.只能在本类当中访问，子类不能访问或者设置
}
@end

//Dog.h
#import "Animal.h"

@interface Dog : Animal
- (void)lookHome;
@end
//Dog.m
#import "Dog.h"

@implementation Dog
- (void)lookHome
{
_age = 1;
//    _weight = 9; // 私有变量,子类不能访问或者设置
NSLog(@"看家......");
}
@end