<!-- Animal类 -->
@interface Animal : NSObject
- (void)animal;
@end
<!-- Animal+Eat分类 -->
@interface Animal (Eat) <NSCopying, NSCoding>
@property (nonatomic, assign) int age;
- (void)eat;
@end
<!-- Animal+Play分类 -->
@interface Animal (Play)
- (void)play;
@end