Is there a post somewhere that can explain step by step the solution and why it works the way it does?

Question

I was able to complete the challenge but have no idea why it works. Just looking for a good reference. Re-watching the video before the challenge hasn't helped me understand the solution.

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 = "";
    return result;
  }
}

Answer 1 · 2016-08-30T20:19:53Z

August 30, 2016 8:19pm

Here is my try to explain:

  public static String getTitleFromObject(Object obj) {
    // 1. For this first task, return the "object obj" type casted as a 
    // String if it is in fact a String. 

    // First we define String "result" to empty String, so that if object 
    // is not String or BlogPost we will return empty String. Could be
    // smarter here, but it is OK for this task.
    String result = ""; 

    // here we check if argument "obj" is indeed "String"
    if (obj instanceof String) {
      // if it is String, we cast "obj" to String and pass it to "result"
      result = (String) obj;
    }

    // 2. 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. 

   // here we check if argument "obj" is indeed "BlogPost"
   if (obj instanceof BlogPost) {
     // if it is BlogPost 
     // 1. we cast "obj" to BlogPost
     BlogPost bg = (BlogPost) obj;
     // 2. we assign `getTitle()` result to our "result" String,
     // to return title of BlogPost passed
     result = bg.getTitle();     
   }

   // finally we return "result" String, whether it is
   // - empty String if "obj" is neither String, nor BlogPost
   // - String casted from "obj", if "obj" is indeed String
   // - Title of BlogPost, if "obj" is BlogPost, and we used getTitle() on it.
   return result; 
  }

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Andrew Rydzakrydza

Andrew Rydzakrydza

Is there a post somewhere that can explain step by step the solution and why it works the way it does?

1 Answer

Alexander Nikiforov

Alexander Nikiforov