第一、淺拷貝：

    Car *car=[[[self class] allocWithZone:zone] init];
    car.engine=_engine;
    car.name=_name;
    car.weight=_weight;
    return car;

測試代碼：

 Car *car = [[Car alloc] init];
        Engine *engine = [[Engine alloc] init];
        car.engine = engine;
        [engine release];
        //NSLog(@"engine retaincount is %lu",[engine retainCount]);
        car.name = @"奧迪";
        car.weight = @1000;

        Car *car2=[car copy];
       // NSLog(@"car2 retaincount is %lu",[car2 retainCount]);
        NSLog(@"car %@,car2:%@",car.engine,car2.engine);

輸出結果：

car ,car2:

可以看出淺復制只是復制指針，並沒有創建新的內存空間

第二、深拷貝：

- (id)copyWithZone:(NSZone *)zone {
    /***淺拷貝**/
    Car *car=[[[self class] allocWithZone:zone] init];
    Engine *engineCopy=[[_engine copy] autorelease];
    car.engine=engineCopy;
    
    NSString *namecopy=[[_name copy] autorelease];
    car.name=namecopy;
    
    NSNumber *weightcopy=[[_weight copy] autorelease];
    car.weight=weightcopy;
    return car;
}

測試代碼：

Car *car = [[Car alloc] init];
        Engine *engine = [[Engine alloc] init];
        car.engine = engine;
        [engine release];
        //NSLog(@"engine retaincount is %lu",[engine retainCount]);
        car.name = @"奧迪";
        car.weight = @1000;

        Car *car2=[car copy];
       // NSLog(@"car2 retaincount is %lu",[car2 retainCount]);
        NSLog(@"car %@,car2:%@",car.engine,car2.engine);

結果：

car ,car2:

開辟了新的空間,zone代表一塊內存空間

 Car *car=[[[self class] allocWithZone:zone] init];

注意上述代碼用的是【self class】，而不是car，因為如果是用car，那麼car的子類在調用此方法去實現copy協議時，就會出現內存問題

另外，當子類繼承了父類時，他繼承了父類的一切屬性，包括要實現的協議

第三、NSFoundation，當我們copy的時一個不可變對象時，默認的copy都是淺拷貝,相當於retain

        NSArray *array =[NSArray arrayWithObjects:@"one",@"two",@"three", nil];
        NSArray *array1 = [array copy];
        NSLog(@"%p",array);
        NSLog(@"%p",array1);
        NSLog(@"the retaincount is %lu",[array retainCount]);

輸出結果：

copyDemo1[673:303] 0x10010a5d0

2013-12-28 20:01:10.969 copyDemo1[673:303] 0x10010a5d0

2013-12-28 20:01:10.969 copyDemo1[673:303] the retaincount is 2

注意retaincount會增加

當使用mutableCopy時，不管對象是否可變，都會實現深拷貝

        NSArray *array =[NSArray arrayWithObjects:@"one",@"two",@"three", nil];
        NSMutableArray *array1 = [array mutableCopy];
        NSLog(@"%p",array);
        NSLog(@"%p",array1);
        NSLog(@"the retaincount is %lu",[array retainCount]);

結果：

copyDemo1[695:303] 0x10010a5d0

2013-12-28 20:07:08.570 copyDemo1[695:303] 0x10010b260

2013-12-28 20:07:08.570 copyDemo1[695:303] the retaincount is 1

第四、retain相當於兩個對象指向同一個指針

        NSMutableArray *array1 = [[NSMutableArray alloc] initWithObjects:@"one",@"two",@"three",@"foure", nil];
        NSMutableArray *array2 = [array1 retain];
        [array2 removeLastObject];
        NSLog(@"%@",array1);
        NSLog(@"the retaincount is %ld",array2.retainCount);

結果：

2013-12-28 20:13:02.915 copyDemo1[736:303] (
    one,
    two,
    three
)
2013-12-28 20:13:02.917 copyDemo1[736:303] the retaincount is 2