iOS中属性和字段之间的差异

Question

有人可以解释一下我们之间究竟有什么区别：

@interface PersistenceViewController : UIViewController { 
    UITextField *field1; 
    UITextField *field2; 
    UITextField *field3;
} 

@property (nonatomic, retain) IBOutlet UITextField *field1; 
@property (nonatomic, retain) IBOutlet UITextField *field2; 
@property (nonatomic, retain) IBOutlet UITextField *field3; 

和

@interface PersistenceViewController : UIViewController { 
} 
@property (nonatomic, retain) IBOutlet UITextField *field1; 
@property (nonatomic, retain) IBOutlet UITextField *field2; 
@property (nonatomic, retain) IBOutlet UITextField *field3; 

他们似乎都以同样的方式工作。