If the object passed is a specific object, convert it and call one of its getters?

Question

So I'm a little bit stuck again. Here's the exercise.

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

I've included BlogPost.java for your reference only

I don't know if I have to do anything with the result string or not. And I don't quite understand why it says that "obj.getTitle();" can't be found, even tho I only call it IF the object is a specific object that has that method. Help please =)

com/example/BlogPost.java

package com.example;

import java.util.Date;

public class BlogPost {
    private String mAuthor;
    private String mTitle;
    private String mBody;
    private String mCategory;
    private Date mCreationDate;

    public BlogPost(String author, String title, String body, String category, Date creationDate) {
      mAuthor = author;
      mTitle = title;
      mBody = body;
      mCategory = category;
      mCreationDate = creationDate;
    }

    public String getAuthor() {
      return mAuthor;
    }

    public String getTitle() {
      return mTitle;
    }

    public String getBody() {
      return mBody;
    }

    public String getCategory() {
      return mCategory;
    }

    public Date getCreationDate() {
      return mCreationDate;
    }
}

TypeCastChecker.java

import com.example.BlogPost;

public class TypeCastChecker {
  /***************
  I have provided 2 hints for this challenge.
  Change `false` to `true` in one line below, then click the "Check work" button to see the hint.
  NOTE: You must set all the hints to false to complete the exercise.
  ****************/
  public static boolean HINT_1_ENABLED = false;
  public static boolean HINT_2_ENABLED = true;

  public static String getTitleFromObject(Object obj) {
    // Fix this result variable to be the correct string

    String result = "";
    if(obj instanceof BlogPost) {
    return obj.getTitle();
    } else {
     return null; 
    }
  }
}

Answer 1 · 2016-05-17T04:52:28Z

May 17, 2016 4:52am

Because obj is declared as an Object, it will only have access to the methods an Object has. It can't access the methods of BlogPost, even if obj happens to be a BlogPost. This is why you need to cast it to a BlogPost before you can access it's methods.

if(obj instanceof BlogPost) {
    BlogPost post = (BlogPost) obj;
    return post.getTitle();
}

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Simon Andersson

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If the object passed is a specific object, convert it and call one of its getters?

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Seth Kroger

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Simon Andersson

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