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Java Java Data Structures Getting There Type Casting

Ilayda Onbilgin
Ilayda Onbilgin
2,391 Points

BlogPost TypeCasting question

I couldn't understand the compiler error

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) {            //if it's a string
      result = (String) obj;               //return a string
    }else if(obj instanceof BlogPost) {    //if it's a blogpost
      BlogPost b = (BlogPost) obj;        //cast it to a blogpost
      result = b.getTitle();            //return the value of getTitle(which will be a string)
    }
 return result;
  }

}

1 Answer

andren
andren
28,558 Points

What happens if your method is passed an object which is neither a String nor a BlogPost? Neither of your if statements would run so you would end up returning a variable which has not been assigned any value, which is not allowed. That's why the compiler complains about the possibility of result never being initialized.

A variable that is returned has to have a value assigned to it at the time of return, regardless of how the method was called. That's mandatory. This issue can be fixed quite easily though, just assign an empty string to result at the beginning like this:

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 = ""; // Initialize result as empty string

    if(obj instanceof String) {            //if it's a string
      result = (String) obj;               //return a string
    } else if(obj instanceof BlogPost) {    //if it's a blogpost
      BlogPost b = (BlogPost) obj;        //cast it to a blogpost
      result = b.getTitle();            //return the value of getTitle(which will be a string)
    }
    return result;
  }
}

If the passed in object is a String or a BlogPost then the value of result will be changed within your if statements, but if it is something else then you'll return an empty String instead which is perfectly valid.