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


When I run this, it says:

':heavy_multiplication_x: Bummer! You should no longer need the cast of BlogPost, that's what generics are for!',

but when I erased the commented cast of BlogPost, I passed the challenge. But the cast was commented.

This was why I think that the challenge has an error.



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 obj) {
    // BlogPost other = (BlogPost) obj;
    if (equals(obj)) {
      return 0;
    return mCreationDate.compareTo(obj.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;

2 Answers

Allan Clark
Allan Clark
10,810 Points

Likely what is going on is that the TreeHouse work checker is looking through your code (before compiling) and making sure that the cast statement does not exist. It is looking through your uncompiled code because after the code is compiled, the results are the same using either method (casting or generics). The compiler differentiates comments but a "find in this document"-like process does not.

I know. I just think that it would be very confusing for others.

trina joy
trina joy
6,525 Points

i had the same problem, and it drove me crazy until i read this!