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Java Java Data Structures - Retired Getting There Type Casting

Mike Papamichail
Mike Papamichail
4,883 Points

Class Type Casting Challenge

I managed to pass the first task of this challenge but i am having trouble with the second one.I can't seem to figure out what i'm doing wrong here.Can someone please offer me a hint?Thank you in advance!

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 = (String) obj;
    if ( obj instanceof BlogPost) {
      BlogPost blog = (BlogPost) obj;
      return blog.getTitle();
    }
    return result;
  }
}

1 Answer

andren
andren
28,558 Points

Your code is close, the issue is that in your first line you convert obj to a String, that works fine if obj really is a String, which is the case in task 1. But in task 2 it is not a String, and casting it to a String when it is not in fact a String causes your program to crash. You should never cast an object if you are not completely sure that it is the right type first.

Fixing this issue is actually pretty simple, all you need to do is check if obj is an instanceof String before you cast it just like you currently do with your BlogPost if statement, instead of setting result directly to a String right away like you are currently doing.

Mike Papamichail
Mike Papamichail
4,883 Points

Thanks a bunch, i don't know why i didn't think about that earlier.