创建一个Person类
Person.h

import<Foundation/Foundation.h>
@interface Person : NSObject
{
    //属性
    NSString *_name;//名字
    int _age;              //年龄
    float _weight;      //体重
}

/*______________________________________________________________________*/
    //方法声明
//set 方法  设置器
- (void)setName:(NSString *)name;
- (void)setAge:(int)age;
- (void)setWeight:(float)weight;

//get方法  访问器
- (NSString *)name;
- (int)age;
- (float)weight;
/*______________________________________________________________________*/

//类方法
+ (void)showPersonMembers;

//实例方法
- (void)setName:(NSString *)name age:(int)age weight:(float)weight;

@end

Person.m

#import"Person.h"
@implementation  Person

//set
- (void)setName:(NSString *)name
{
    _name = name;
}

- (void)setAge:(int)age
{
    _age = age;
}

- (void)setWeight:(float)weight
{
    _weight = weight;
}
/*_______________________________________________________________*/
//get
- (NSString *)name
{
    return _name;
}

- (int)age
{
    return _age;
}

- (float)weight
{
    return _sweight;
}
/*_________________________________________________________________*/
//类方法
+ (void)showPersonMembers
{
    NSLog(@"members : name age sweight");
}

//实例方法
- (void)setName:(NSString *)name  age:(int)age weight:(float)weight
{
    [self setName:name];
    _age = age;
    _weight = weght;

    //调用本类的实例方法  使用 --> self 表示本类的对象
    [self privateMethod];

    //调用本类的类方法  使用  -->  类名
    [Person classPrivateMethod];
}
/*______________________________________________________________________*/
//如果一个方法实现在 .m 文件中，而没有在对应的 .h 文件中声明  那么这是一个私有的方法
- (void)privateMethod
{  
    NSLog(@"私有方法");
}

+ (void)classPrivateMethod
{
    NSLog(@"私有的类方法")；
}

/*________________________________________________________________________*/

//description 方法   方法覆写
- (NSString *)description
{
    //决定了  使用%@打印对象时  控制台所展示的内容
    return [NSString stringWithFormat:@"Person:%p name:%@ age:%d weight%,1f",self,_name,_age,_weight];
}
@end

main.m

#import<Foundation/Foundation.h>
#import"Person.h"
int main(int argc,const char *argv[])
{
  @autoreleasepool
  {
     //类 创建 对象
          //1.开辟内存
    Person *xiaoming = [Person alloc];

          //2.初始化
    xiaoming  = [xiaoming init];

          //建议写法：一次完成
    Person *xiaohong = [[Person alloc]init];
/*_____________________________________________________________________*/
    //设置属性
    [xiaohong setName:@"小红"]；
    [xiaohong setAge:18];
    [xiaohong setWeight:120];
    [xiaohong setName:@"小红"]；
/*_______________________________________________________________________*/
    //访问属性
    NSLog("name = %@ age = %d weight = %f",[xiaohong name],[xiaohong age],[xiaohong weight]);

/*_______________________________________________________________________*/

//类  调用  类方法
[Person showPersonMembers];


NSLog(@"xiaohong  is  %@"xiaohong);
  }
   return 0;
}