@interface NSObject <NSObject> {

    Class isa  OBJC_ISA_AVAILABILITY;

}

// 初始化加载

+ (void)load;

// 初始化对象

+ (void)initialize;
// 初始化对象，分配内存

- (instancetype)init;

// 分配一个新的接受类实例，并发送init消息，返回初始化对象

+ (instancetype)new;
// init后系统自动调用该方法，用于内存分配

+ (instancetype)allocWithZone:(struct _NSZone *)zone;
// 内存中为一个对象分配内存，并返回实例

+ (instancetype)alloc;
// 用于类释放对象实例并释放动态内存

- (void)dealloc;

// 标明该对象需要释放

- (void)finalize;

// 复制一个imutable的对象

- (id)copy;
// 复制一个mutable的对象

- (id)mutableCopy;

// <NSCopying>协议后实现的copy方法

+ (id)copyWithZone:(struct _NSZone *)zone;
// <NSCopying>协议后实现的mutablecopy方法

+ (id)mutableCopyWithZone:(struct _NSZone *)zone;

// 类是否存在该方法

+ (BOOL)instancesRespondToSelector:(SEL)aSelector;
// 类是否实现该协议

+ (BOOL)conformsToProtocol:(Protocol *)protocol;
// 返回对象中指定的函数指针

- (IMP)methodForSelector:(SEL)aSelector;
// 返回类中指定的函数指针

+ (IMP)instanceMethodForSelector:(SEL)aSelector;
// 该对象找不到对应的实现方法时执行该方法，用于抛出异常

- (void)doesNotRecognizeSelector:(SEL)aSelector;

// 若返回非nil，非self，则将详细转发给该对象，否则继续其他流程

- (id)forwardingTargetForSelector:(SEL)aSelector;
// 与上一个类似，但该方法可转发给多个对象，是最后一个寻找IML的机会

- (void)forwardInvocation:(NSInvocation *)anInvocation;
// 让重载方有机会抛出函数签名，再由上一个方法执行

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;

// 同上，该方法为类方法

+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector;

// 对象是否支持weak

- (BOOL)allowsWeakReference UNAVAILABLE_ATTRIBUTE;
// 对象是否支持retain，weak

- (BOOL)retainWeakReference UNAVAILABLE_ATTRIBUTE;

// 是否为该类的子类

+ (BOOL)isSubclassOfClass:(Class)aClass;

// 当执行不存在的类方法时，调用该方法，默认返回NO，加上自己的处理后可返回YES

+ (BOOL)resolveClassMethod:(SEL)sel;
// 同上，但该方法为雷芳法

+ (BOOL)resolveInstanceMethod:(SEL)sel;

// hash值

+ (NSUInteger)hash;
// 方法调用者的父类类名

+ (Class)superclass;
// 方法调用者的类名

+ (Class)class;
// 对象描述，可自己实现

+ (NSString *)description;
// 调试对象描述

+ (NSString *)debugDescription;

@end

@protocol NSObject

- (BOOL)isEqual:(id)object;

@property (readonly) NSUInteger hash;

@property (readonly) Class superclass;
// 返回类名

- (Class)class;
// 是一个指针，地址指向当前类

- (instancetype)self;

// 单线程，等包含该函数的方法执行完后才执行指定的方法

- (id)performSelector:(SEL)aSelector;
// 同上

- (id)performSelector:(SEL)aSelector withObject:(id)object;
// 同上

- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;

// 对象是否为代理

- (BOOL)isProxy;

// 对象是否为指定类

- (BOOL)isKindOfClass:(Class)aClass;
// 对象是否为成员类

- (BOOL)isMemberOfClass:(Class)aClass;
// 是否实现对应协议

- (BOOL)conformsToProtocol:(Protocol *)aProtocol;

// 是否需执行对应方法

- (BOOL)respondsToSelector:(SEL)aSelector;

// 

- (instancetype)retain OBJC_ARC_UNAVAILABLE;
// 

- (oneway void)release OBJC_ARC_UNAVAILABLE;
// 

- (instancetype)autorelease OBJC_ARC_UNAVAILABLE;
// 

- (NSUInteger)retainCount OBJC_ARC_UNAVAILABLE;

// 

- (struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;

@property (readonly, copy) NSString *description;

@optional

@property (readonly, copy) NSString *debugDescription;

@end