Completely Stuck in this TypeCasting exercise.

Question

I'm completely lost in the subject of typecasting. I think the video provided very few information about it, and the information it provided was really confusing. I understand the basic concept of typecasting between primitive data types. But I'm completely lost when using objects etc. No idea what is used for, no idea on how to use it... With that said, I'm clueless on how to complete the exercise in typecasting.

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 = true;

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

Answer 1 · 2017-06-07T17:04:25Z

June 7, 2017 5:04pm

For Part 1 of challenge, just check if object is of type String, and if so, cast it as such to the result variable:

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

Then for Part 2, check if object is of type BlogPost, and if so, cast it as such and get its title (which is a string):

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

Regarding your questions on what casting objects is used for ... One example is if you're using inheritance to subclass into a variety of child classes, but your data structure is typed to the superclass, and then you may want to check to make sure a particular object in that data structure is of a particular subclass before down-casting it so that you can perform functionality specific to that subclass. Somewhat like in the exercise, where Object is the ultimate superclass, so the getTitleFromObject method will accept an argument of any type passed into it, but based on what the particular type actually is, you know specifically which functionality to perform for that type to yield the desired result.

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dojewqveaq

dojewqveaq

Completely Stuck in this TypeCasting exercise.

1 Answer

David Lin

David Lin

Remus Cordea

Remus Cordea

David Lin

David Lin