title: why declare Object in @interface When used @property In Xcode 4
body: <pre><code>@interface first : &lt;NSObject&gt; {
     NSString *myStr;
    /**
         I don't understand why declared this NSString *myStr.
         Even if not declare NSString *myStr, this codes work well.
    **/
  }
  @property (nonatomic, retain) NSString *myStr;
  
  and Add @synthesize to first.m
  </code></pre>
  
  <p>Is it correct that I don't need to declare myStr as an instance variable if I always use the myStr property, i.e. self.myStr?</p>