incompatible types ERROR

Question

I can't understand the error. When 'else if' statement is executed, doesn't it mean that obj is instance of BlogPost? I just want to make clear obj is BlogPost type by BlogPost-typecasting.

How can i fix 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) {
    // Fix this result variable to be the correct string.
    if( obj instanceof String)
      return (String)obj;
    else if (obj instanceof BlogPost){
      return (BlogPost) obj;
    }
    else {
      String result = "";
      return result;
      }
  }
}

Answer 1 · 2015-08-17T18:17:03Z

August 17, 2015 6:17pm

The problem with your method is that you can not return a BlogPost because the return type is specified as String. Yes you can cast the object to BlogPost, that is correct, but you must return a String, in this case the title of the post.

public static String getTitleFromObject(Object obj) {   
    if( obj instanceof String)
      return (String)obj;
    else if (obj instanceof BlogPost){
      BlogPost post = (BlogPost)obj;
      return post.getTitle();
    }
    else {
      String result = "";
      return result;
      }
  }

If you are comfortable with the syntax of casting you can write this:

public static String getTitleFromObject(Object obj) {   
    if( obj instanceof String)
      return (String)obj;
    else if (obj instanceof BlogPost){
      return ((BlogPost)obj).getTitle();
    }
    else {
      return "";
    }
}

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Kate Lee

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incompatible types ERROR

1 Answer

Enrique Munguía

Enrique Munguía