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Java Java Data Structures - Retired Getting There Type Casting

pratham daswani
pratham daswani
979 Points
Posted by pratham daswani
pratham daswani
979 Points

Typecasting

How to solve this question , what is asked basically?

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 = true;
  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;

  }
}

2 Answers

Kourosh Raeen
Kourosh Raeen
23,733 Points
Kourosh Raeen
Kourosh Raeen
23,733 Points

For this challenge you need to use the instanceof keyword to check the type of a variable and then based on the type do the appropriate casting. For example, if the variable obj is of type Foo then you can cast it like this:

result = (Foo) obj;

You can use instanceof in an if statement. For example, to see if obj is of type Foo you can do this:

if (obj instanceof Foo) {
   // Do your type casting here

}
Simon Coates
Simon Coates
28,694 Points
Simon Coates
Simon Coates
28,694 Points

The following seems to pass the test.

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

    String result = "";
    return result;
  }

Kourosh Raeen explains the ideas pretty well.