NSLog(@"object =%@",object);

● +string//用于创建新的空字符串
● +stringWithString//工厂方法，用于根据某字符串创建新的字符串
● +localizedStringWithFormat://工厂方法，格式化本地字符串
● -lowercaseString//把字符串中的大写字母全部转化位小写
● -intValue//将字符串解析为整数
● -length//获取字符串长度
● -lengthOfBytesUsingEncoding://若字符串是以给定的编码格式
● -getCharacters:range://获取字符串给定范围的字符
● -(void)getCharacters:(unichar*)buffer range:(NSRange)aRange//首个参数应该指向一个足够大的数组，以便容下请求范围内的那些字符串
● -hasPrefix://是否有某个前缀
● -isEqualToString://判断字符串是否相等

-(id)copyWithZone:(NSZone*)zone

#import<Foundation/Foundation.h>

@interface EOCPerson :NSObject<NSCopying>
@propetry (nonatomic,copy,readonly) NSString *firstName;
@propetry (nonatomic,copy,readonly) NSString *lastName;
-(id) initWithFirstName:(NSString*)firstName andLastName:(NSString*)lastName;
-(void)addFriend:(EOCPerson*) person;
-(void)removeFriend:(EOCPerson*)person;
@end
@implementation EOCPerson{
NSMutableSet *_friends;
}

-(id) initWithFirstName:(NSString*)firstName andLastName:(NSString*)lastName{
    if((self = [super init])){
        _firstName = [firstName copy];
        _lastName = [lastName copy];
        _friends = [NSMutableSet new];
    }
    return self
}
-(void)addFriend:(EOCPerson*)person{
    [_friends addObject:person];
}
-(void) removeFriend:(EOCPerson*)person{
    [_friends removeObject:person];
}
-(id)copyWithZone:(NSZone)zone{
    EOCPerson *copy =[[[self class]allocWithZone:zone] initWithFirstName:_firstName andLastName:_lastName];
    copy->_friends = [_friends mutableCopy];
    return copy
}
@end

-(id)initWithSet:(NSArray*)array copyItems:(BOOL)copyItems

   // 非容器类对象
    NSString *str = @"origin string";
    NSString *strCopy = [str copy];
    NSMutableString *mstrCopy = [str mutableCopy];
    [mstrCopy appendString:@"??"];

 NSMutableString *mstr = [NSMutableString stringWithString:@"origin"];
    NSString *strCopy = [mstr copy];
    NSMutableString *mstrCopy = [mstr copy];
    NSMutableString *mstrMCopy = [mstr mutableCopy];
    //[mstrCopy appendString:@"1111"];  //error
    [mstr appendString:@"222"];
    [mstrMCopy appendString:@"333"];