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Java Java Data Structures Getting There Type Casting

Simon Feuster
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Simon Feuster
Full Stack JavaScript Techdegree Graduate 28,036 Points

Return object obj type casted as a String if it is in fact a String

Can someone help me please. I don't get it :(

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

2 Answers

You need to cast obj to String when setting result = obj

result = (String) obj;
Rares Conea
PLUS
Rares Conea
Courses Plus Student 15,000 Points

Even if obj is of type String and the if statement evaluates to true the assigning you are trying to do won t compile because Object is a super type of String. When trying to cast from supertype to subtype you need to add the type of the subtype you want in (), as in the example "result = (String) obj"(Downcastig), while the oposite can be done without casting "An Object reference can point to anything(because Object is the class from which all other classes inherit) without casting <obj = result> will compile"(Upcasting does not require ())