属性的特性

//nonatomic：非原子性（线程不安全的），线程安全会影响系统性能，造成卡顿
//assign：不实行oc中的内存管理机制，通常用于修饰非对象类型，如int float
//retain：实行oc中的内存管理机制，通常用于修饰对象类型，如 NSString
//readonly：只读的，只生成getter方法，不生成setter方法

Car.h
#import 
@interface Car : NSObject

@property (nonatomic,retain) NSString * brand;
@property (nonatomic,assign) NSInteger price;
@property (nonatomic,retain) NSString * color;
+ (instancetype)carWithBrand:(NSString *)brand price:(NSInteger)price color:(NSString *)color;

- (instancetype)initWithBrand:(NSString *)brand price:(NSInteger)price color:(NSString *)color;
@end

Car.m
#import "Car.h"

@implementation Car
//便利构造器
+ (instancetype)carWithBrand:(NSString *)brand price:(NSInteger)price color:(NSString *)color{
    return [[Car alloc]initWithBrand:brand price:price color:color ];
}
//自定义初始化方法
- (instancetype)initWithBrand:(NSString *)brand price:(NSInteger)price color:(NSString *)color{
    self = [super init];
    if (self) {
        _brand = brand;
        _price = price;
        _color = color;
    }
    return self;
}
@end

main.m
    Car *car = [Car carWithBrand:@"BYD" price:120000 color:@"black"];
    NSLog(@"%@,%ld,%@",car.brand,car.price,car.color);
    car.brand = @"BMW";
    NSLog(@"brand:%@",car.brand);