//1. NSArray        EOItems *eOItems = [[EOItems alloc] init];    eOItems.ID = [NSNumber numberWithInt:1];    NSArray *arr = [NSArray arrayWithObjects:eOItems, nil];    eOItems.ID = [NSNumber numberWithInt:2];    NSLog(@"eOItems.ID =%@, ((EOItems *)[arr objectAtIndex:0]).ID=%@", eOItems.ID, ((EOItems *)[arr objectAtIndex:0]).ID);    //打印结果: eOItems.ID =2, ((EOItems *)[arr objectAtIndex:0]).ID=2        EOItems *eOItems2 = [arr objectAtIndex:0];    eOItems2.ID = [NSNumber numberWithInt:22];    NSLog(@"eOItems2 =%@, ((EOItems *)[arr objectAtIndex:0]).ID=%@", eOItems2.ID, ((EOItems *)[arr objectAtIndex:0]).ID);    //打印结果: eOItems2 =22, ((EOItems *)[arr objectAtIndex:0]).ID=22        NSLog(@"eOItems.ID =%@", eOItems.ID);    //打印结果:eOItems.ID =22        //由此可见: NSArray只是存储对象的索引并没有真正复制对象, 对象由始至终只有一个        //2.NSMutableArray        NSMutableArray *mutableArray = [arr mutableCopy];    ((EOItems *)[mutableArray objectAtIndex:0]).ID = [NSNumber numberWithInt:333];    NSLog(@"eOItems.ID=%@", eOItems.ID);    NSLog(@"eOItems2.ID=%@", eOItems2.ID);    NSLog(@"((EOItems *)[mutableArray objectAtIndex:0]).ID=%@", ((EOItems *)[mutableArray objectAtIndex:0]).ID);    //输出结果    //eOItems.ID=333    //eOItems2.ID=333    //((EOItems *)[mutableArray objectAtIndex:0]).ID=333        //经NSArray mutableCopy得来的 NSMutableArray, 对象也始终只有一个        NSMutableArray *mulArr = [NSMutableArray array ];    EOItems *mulItems = [[EOItems alloc] init];    mulItems.ID = [NSNumber numberWithInt:111];    [mulArr addObject:mulItems];    ((EOItems *)[mulArr objectAtIndex:0]).ID = [NSNumber numberWithInt:222];    NSLog(@"mulItems.ID=%@, ((EOItems *)[mulArr objectAtIndex:0]).ID=%@",mulItems.ID, ((EOItems *)[mulArr objectAtIndex:0]).ID);    //输出结果    //mulItems.ID=222, ((EOItems *)[mulArr objectAtIndex:0]).ID=222        mulItems.ID = [NSNumber numberWithInt:333333];    NSLog(@"mulItems.ID=%@, ((EOItems *)[mulArr objectAtIndex:0]).ID=%@",mulItems.ID, ((EOItems *)[mulArr objectAtIndex:0]).ID);    //输出结果    //mulItems.ID=333333, ((EOItems *)[mulArr objectAtIndex:0]).ID=333333

EOItems *item1 = [[EOItems alloc] init];    item1.ID = [NSNumber numberWithInt:1];        EOItems *item2 = [[EOItems alloc] init];    item2.ID = [NSNumber numberWithInt:2];        EOItems *item3 = item1;    NSLog(@"item3.ID=%@", item3.ID);        item3 = item2;    NSLog(@"item3.ID=%@", item3.ID);