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Java Java Data Structures - Retired Getting There Type Casting

Java Data Structures. Challenge 1 of 2

i need to return obj as String if it is a String.

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;
  }
}

I don't understand where does he get this Object obj, and how i should make it String!

The obj is passed into the method - it doesn't matter where it comes from - it's inside your method and called obj - that's all we need to know.

7 Answers

Hi there,

Use instanceof to see if the obj is a String. If it is, cast it to String and return that.

Start with the if. The condition is the instanceof expression. Inside the if return the cast obj.

Let me know how you get on.

Steve.

I think of casting as in casting an actor to a character. So, you take a Will Smith and cast him as Robert Neville in I Am Legend. It converts the data type.

Anyway, for the last part of the challenge, cast to BlogPost, then put more brackets all round that and use dot notation on the last bracket to call the getTitle() method. That brings a string back, which you want to return.

You can either do that in the else clause, or you can create a new if statement to test using insdtanceof. That's unnecessary, though as we know that obj is either a String or a BlogPost. So, if it isn't a string, it's a blog.

I hope that helps.

Steve.

incompatible types: Object cannot be converted to String

i just wrote

if ( obj instanceof String){
 return obj;
}

But the video says that i can fix it with the name of the class. String obj = (name_of_the_class) obj??

Yes! So put String in brackets before obj in your return line.

OK - that's fine - but cast obj when you return it. Put (String) before obj in your return line.

Why i put (String) and i can't put just String(i tryed and failed)

That's the way the language works - to cast to a type, the brackets are needed. When you declare something, they're not needed. Have you put (String) in your return line?

Yes. It worked, Thank you for that, but i just wanted to know why i put brakets. Thx again

It's just one of those things - that's how casting works. No idea why it's needed technically!