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Java Java Data Structures - Retired Getting There Type Casting

Posted by Ryan Moore
Ryan Moore
Courses Plus Student 1,241 Points

Why use toString() if we know the object is a string?

I just used an if() statement to determine whether or not obj is a string. This doesn't feel right to me. It's redundant. Sure, it prevents us from getting an error (because apparently obj is not a string) but that's a kludge. The purpose of that is unclear. I feel like there has to be a better way, one more suitable to the purpose of whatever method is being called.

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 = obj.toString();}
    return result;
  }
}

1 Answer

Kevin Faust
Kevin Faust
15,353 Points
Kevin Faust
Kevin Faust
15,353 Points

Hey Ryan,

This lesson and challenge is just to make sure you understand typecasting and why it's used

Obviously we can just do this:

 public static String getTitleFromObject(String obj)

I don't know if you learned generics yet (I believe you will learn it soon) but once you do, you most likely won't be using this tbh

Ryan Moore
Ryan Moore
Courses Plus Student 1,241 Points

Ah, yes. For some reason typecasting didn't even occur to me until I posted this question, then I glanced at the method I called and immediately realized I was supposed to be using a typecast. The typecast feels much less distasteful (for lack of a better term) than toString().

Kevin Faust
Kevin Faust
15,353 Points
Kevin Faust
Kevin Faust
15,353 Points

Oh sorry I misread what you wrote. I thought you were asking why we do typecasting lol

if(obj instanceof String) {
    result = obj;
    return result;
  }

Reading your comment I believe you figured it out but I just wanted to make sure. Since the if block can only run if our obj is a String, we can directly assign obj to our result string if it passes the "if" statement. no need for the toString() method ;)