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Java Java Data Structures - Retired Getting There Type Casting

Posted by dlpuxdzztg
dlpuxdzztg
8,243 Points

Not sure what the 2nd challenge is asking me to do...

So the description:

Now make sure that if a com.example.BlogPost is passed in for obj that you can cast it to a BlogPost. Return the results of the getTitle method on the newly type-casted BlogPost instance.

I am very confused what most of this means and what it is telling me to do.

Please Help!

2 Answers

srikarvedantam
srikarvedantam
8,369 Points

The challenge asks to check for the types of the Object instance (obj) specified and type-cast accordingly. Here is what the challenge expects us to do:

  public static String getTitleFromObject(Object obj) {
    // Fix this result variable to be the correct string.
    String result = "";
    // Check if obj is of type 'String' and type-cast to String type if it indeed is.
    if(obj instanceof String) {
      result = (String) obj;
    }
    // Otherwise, check if obj is of type 'BlogPost'
    // and invoke the getTitle() method after type-casting.
    else if(obj instanceof BlogPost){
      BlogPost blogPost = (BlogPost) obj;
      result = blogPost.getTitle();
    }
    return result;
  }
dlpuxdzztg
dlpuxdzztg
8,243 Points

Thanks! But..."else if"? I'm not sure we ever covered that, why not just use "else" instead?

srikarvedantam
srikarvedantam
8,369 Points
srikarvedantam
srikarvedantam
8,369 Points

If we use "else" instead of "else if (...)", then when an object of any type other than "String" (not only "BlogPost", but also any other type) is passed, then the method will try to type cast it BlogPost which may result in a ClassCastException (if obj is not of type 'BlogPost'). So, we need to ensure that the obj specified is indeed of type 'BlogPost' and hence the conditional check with "else if(...)".