title: Check if NSString instance is contained in an NSArray
body: <p>I have an array with a bunch of strings and I want to check if a certain string is contained in the array. If I use the <code>containsObject</code>: message on the array, I'm getting correct results. Do all <code>NSString</code> objects with the same string point to the same object? Or why is the <code>containsObject</code>: working?</p>
  
  <pre><code>NSArray *stringArray = [NSArray arrayWithObjects:@"1",@"2",@"3",anotherStringValue, nil];
  if([stringArray containsObject:@"2"]){
    //DO SOMETHING
  }
  </code></pre>