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Java Java Data Structures Getting There Type Casting

gaetan mertens
gaetan mertens
1,002 Points
Posted by gaetan mertens
gaetan mertens
1,002 Points

access a method from another class

I can't access the method getTitle().

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 = false;

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

    if (obj instanceof String) {
    result = (String) obj;
    }
    if (obj instanceof BlogPost) {
      result = (String) obj.getTitle();
    }
    return result;
  }
}
Steven Snary
Steven Snary
17,540 Points
Steven Snary
Steven Snary
17,540 Points

Good Evening Gaetan,

I'm going to assume that you passed the 1st step - returning the result when obj is a String since the code that you wrote in that section works fine.

In step 2 you must first cast the obj (Object) to the Type BlogPost using something like this:

BlogPost post = (BlogPost)obj;

Then you should be able to call the getTitle method on the new post object of Type BlogPost and set that to result. ( You shouldn't have to cast to String the post object as the getTitle() method will do that for you if I'm remembering that code correctly )

***Note: this has nothing to do with why your code isn't passing - but you can also use the following statement in step 1:

result = obj.toString();

I only point this out because you may also see code that uses the built-in toString() method in Java

1 Answer

michaelcodes
michaelcodes
5,604 Points
michaelcodes
michaelcodes
5,604 Points

Hi There! The problem here is that you are trying to call the method directly from the generic object. First we must typecast the generic object to a BlogPost. From here we can call the method from the from the typecasted BlogPost as such:

  public static String getTitleFromObject(Object obj) {
    // Fix this result variable to be the correct string.
    String result = "";
    BlogPost bp;
    if(obj instanceof String) {
      result = (String) obj;
    }
    if(obj instanceof BlogPost) {
      bp = (BlogPost) obj;
      result = bp.getTitle();
    }
    return result;
  }
}

You actually don't even need to declare the object outside of the scope, it can go together as 1 line as such:

BlogPost bp = (BlogPost) obj;