#import <Foundation/Foundation.h>/**************************************** * Person类 ****************************************/// 要采用某个协议，需要在类的声明中列出该协议的名称，并用尖括号括起来// 同时采用多个协议，则在协议的名称之间用逗号分割，如：<NSCopying, NSCoding>// 可以按任意顺序列出多个协议@interface Person : NSObject <NSCopying>@property (nonatomic, copy, readwrite) NSString* name;@end@implementation Person// copyWithZone:方法的返回类型为id，参数类型为NSZone- (id)copyWithZone:(NSZone*)zone {        // 通过使用[self class]，allocWithZone:消息将会被发送给正在接受copy消息的对象所属的类    // 这个类可能是copyWithZone:消息所在类的子类，通过这种方式可以正确的创建想要的对象    // 如果不使用[self class]，而使用具体的类名，可能导致创建得到的实例无法返回给类型正确的实例指针    // allocWithZone:方法是一个类方法，其最后一行返回新创建的实例    // zone是NSZone类的一个实例，指向一块可供分配的内存区域    Person* personCopy = [[[self class] allocWithZone:zone] init];        // 复制实例变量或属性    [personCopy setName:[self name]];        // 返回新创建的对象    return personCopy;}- (NSString*)description {    return [NSString stringWithFormat:@"[name = %@]", [self name]];}- (void)dealloc {    [[self name] release];    [super dealloc];}@end/**************************************** * GoodPerson类 ****************************************/// 父类采用了某个协议，其子类也将遵守该协议，无需用不必要的代码说明@interface GoodPerson : Person@property (nonatomic, assign, readwrite) NSUInteger age;@end@implementation GoodPerson- (id)copyWithZone:(NSZone*)zone {    // 由于父类已经实现了copyWithZone:方法    // 子类只需调用该方法，并完成属于自己需要负责的那部分复制操作即可    GoodPerson* goodPersonCopy = [super copyWithZone:zone];        [goodPersonCopy setAge:[self age]];        return goodPersonCopy;}- (NSString*)description {    return [NSString stringWithFormat:@"[name = %@, age = %lu]", [self name], [self age]];}@end/**************************************** * main函数 ****************************************/int main(int argc, const char * argv[]) {    Person* p1 = [[Person alloc] init];    [p1 setName:@"AAA"];        // 当向一个实例发送copy消息时，则该copy消息会被转换为调用copyWithZone:方法    Person* p2 = [p1 copy];    NSLog(@"Address(p1) = %p, retainCount(p1) = %lu", p1, [p1 retainCount]);    NSLog(@"Address(p2) = %p, retainCount(p2) = %lu", p2, [p2 retainCount]);        NSLog(@"p1%@", p1);    NSLog(@"p2%@", p2);        [p1 release];    [p2 release];        GoodPerson* gp1 = [[GoodPerson alloc] init];    [gp1 setName:@"BBB"];    [gp1 setAge:20];        GoodPerson* gp2 = [gp1 copy];    NSLog(@"Address(gp1) = %p, retainCount(gp1) = %lu", gp1, [gp1 retainCount]);    NSLog(@"Address(gp2) = %p, retainCount(gp2) = %lu", gp2, [gp2 retainCount]);        NSLog(@"gp1%@", gp1);    NSLog(@"gp2%@", gp2);        [gp1 release];    [gp2 release];        return 0;}

Address(p1) = 0x1002021b0, retainCount(p1) = 1Address(p2) = 0x1002021c0, retainCount(p2) = 1p1[name = AAA]p2[name = AAA]Address(gp1) = 0x100205170, retainCount(gp1) = 1Address(gp2) = 0x1002053d0, retainCount(gp2) = 1gp1[name = BBB, age = 20]gp2[name = BBB, age = 20]