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Java Java Data Structures - Retired Exploring the Java Collection Framework Upgrade Comparable to use Generics

Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Generics problem....

In this challenge we added the generic <BlogPost> to the Comparable class. So we can use the BlogPost object other in the compareTo method directly . But why we delete the initialisation of the BlogPost????

BlogPost other = (BlogPost) obj;
com/example/BlogPost.java
package com.example;

import java.io.Serializable;
import java.util.Date;

public class BlogPost implements Comparable<BlogPost>, Serializable {
  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 int compareTo(BlogPost other) {
    //BlogPost other = (BlogPost) obj;
    if (equals(other)) {
      return 0;
    }
    return mCreationDate.compareTo(other.mCreationDate);
  }

  public String[] getWords() {
    return mBody.split("[^\\w']+");
  }

  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;
  }
}

1 Answer

The operation in the line you refer to

BlogPost other = (BlogPost) obj;

is called typecasting. It's not initialization. If you remember correctly, we changed the parameter inside the parenthesis to type BlogPost. It used to be of type Object so we had to typecast it to BlogPost. However, now that it is of the correct type, there is no need to typecast it. Hope that clears it.