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Java Java Data Structures - Retired Getting There Type Casting

Priyatham Kunarapu
Priyatham Kunarapu
1,350 Points
Posted by Priyatham Kunarapu
Priyatham Kunarapu
1,350 Points

Help:

I'm not understanding how to solve this.Please help me.

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 BlogPost){ 
    result = (BlogPost) obj;
    }
    return result;
  }
}

2 Answers

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hi Priyatham,

let me explain the first TASK :

public static String getTitleFromObject(Object obj) {
// getTitleFromObject takes an Object as argument
// in Java everything is an object except primitives like "int", "double" etc...
// so you can give a Treet or BlogPost as argument because they are objects
// the problem is that the compiler doesn´t know what kind of object you gave as argument (just you know it!!!)
// Treet is an object so the compiler accepts it, but has no clue which object it is
// so you have to tell the comiler which kind of object you gave as argument
// so you need to cast/convert/specify it (telling which kind the object is)

String result = ""; 
    if(obj instanceof String) { 
// the line above means
// if the argument obj (Object) is an instance of the String class 
// then it should be an object of String class
// do the line below

      result = (String)obj;
// tells the compiler that our argument is an object of kind of String and not only an undefined object
    }
    return result;
  }

For the second TASK you need to proof and cast obj to BlogPost. After casting you can access the getTitle method from the BlogPost class to store the tilte into result and return it if obj is instanceof BlogPost.

Your complete code can look like this:

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 BlogPost) {
     result = ((BlogPost)obj).getTitle(); 
    }
    return result;
// so the returned result will be a String if opbj is a String
// and a Title (a String too) if obj is a BlogPost
  }

Let me know if it was helpfull ...

Grigorij

Priyatham Kunarapu
Priyatham Kunarapu
1,350 Points
Priyatham Kunarapu
Priyatham Kunarapu
1,350 Points

Hi Grigorij,

That was an Awesome Explanation. You kinda explained it in a clear and better than @Craig. I personally appreciate your concern and value your time. I have some doubts in the previous sessions too to get cleared. Will you mind asking you?

Thanking you.

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hey there,

you can ask me anytime. I will try to help you :)

Grigorij