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Java Java Data Structures Getting There Type Casting

Posted by jasongu
jasongu
825 Points

com.example.BlogPost typecasting question on Challenge Task

I got stuck on this last task in the first part of Data Structure course.

This is what I have so far and it's not working.. I couldn't figure out how to return the results of the getTitle method on the newly type-casted BlogPost instance.

I'm also not sure whether the if statement for "if a com.example.BlogPost is passed in for obj that you then cast it to a BlogPost" is right below either..

Please help!

public static String getTitleFromBlogPost(Object obj) { BlogPost result; if (obj instanceof com.example.BlogPost) { result = (BlogPost) obj; return result.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 = obj.toString();
    } else { 
      result = (String) obj;
    }
    return result;
  }

  public static String getTitleFromBlogPost(Object obj) {
    BlogPost result;
    if (obj instanceof com.example.BlogPost) {
      result = (BlogPost) obj;
      return result.getTitle();
    }
  }
}

2 Answers

Rob Bridges
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.a{fill-rule:evenodd;}techdegree seal-36
Rob Bridges
Full Stack JavaScript Techdegree Graduate 35,467 Points
Rob Bridges
.a{fill-rule:evenodd;}techdegree seal-36
Rob Bridges
Full Stack JavaScript Techdegree Graduate 35,467 Points

Hey Jason,

We don't need to create a brand new method to get the title form a blogPost, we can add another if checker to see if it's a blogPost and cast it in there.

Your complete getTitleFromObject method should look like below.

public static String getTitleFromObject(Object obj) {
    if (obj instanceof String) {
      return (String) obj;
    }
    else if (obj instanceof BlogPost) {
      BlogPost myBlogPost = (BlogPost) obj;
      return myBlogPost.getTitle();
    }
    return "";
  }
}

I gave a bit more of a detailed explanation in here

But you were close, just combine it into one method, and you should be set.

Thanks.

jasongu
jasongu
825 Points

Thanks for the answer! I will look at the detailed explanation, it looks very detailed indeed :) Thanks!