Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Java Java Data Structures - Retired Getting There Type Casting

Modure Rares
PLUS
Modure Rares
Courses Plus Student 9,041 Points

Please help me (upcasting and downcasting)

I didn't understand anything from this video. Please help me with this task.

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.
    obj = new BlogPost("title", "title2", "title3", new Date());
    String result = obj.getTitle();
    return result;
  }
}

2 Answers

samiff
samiff
31,206 Points

The challenge states that you are either being passed a String or BlogPost, but the method parameter type is simply Object. If you're receiving a String for that Object parameter, you need to cast the obj variable as a String, because that is the return type of the method. We can check types with instanceof.

In your code you are trying to create a new BlogPost object, but that's not the case for this challenge. We may be receiving an actual BlogPost object itself, so no need to create one. Again, instance of will allow us to see if the passed parameter obj is in fact of type BlogPost. If it is, we can cast the obj to a BlogPost to access the BlogPosts getTitle() method. Please let me know if I can help any further.

String result = "";
if (obj instanceof String) result = (String) obj;  // Challenge part one.
else if (obj instanceof BlogPost) result = ((BlogPost) obj).getTitle(); // Challenge part two.
return result;

I feel like I'm trying to read Hebrew or Japanese :( :( :(