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Java Java Data Structures Getting There Type Casting

Shane May
Shane May
5,114 Points

Java casting! I think I'm headed in the right direction but I'm not sure, please help.

I'm on the last challenge of the Java Data Structure and I am completely stuck. I've included the instructions below as well as my attempt to figure this challenge. Could anyone clear this up for me? I appreciate any help.

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

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 com.example.BlogPost){
     result = (BlogPost.getTitle());
    }
    return result;
  }
}

1 Answer

Jacob Bergdahl
Jacob Bergdahl
29,118 Points

Try this :)

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

Let me know if you need more help understanding the code!

Shane May
Shane May
5,114 Points

It worked. I understand what you did, I just had a hard time with the instructions. Also casting and storing values at the same time is not super clear to me. Thank you for helping me.

I'm greatly confused by this challenge and a little by your answer. So is my understanding of this correct?

in the Else if part, if obj is an instance com.example.BlogPost the code statements between the "{}" is executed.

You create a new blogPost instance that has the value of obj that is casted to com.example.BlogPost.

then result is set to that new instance with the getTitle method chained to the end .

At the very end of the getTitleFromObject() you return the result which would be the title of obj?

Steven MacDiarmid
Steven MacDiarmid
11,339 Points

This really helped me out too so thanks Jacob, Just one thing to add, you don't need to prefix BlogPost with 'com.example' as it has already been imported at the top of the file.