Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Java Java Data Structures - Retired Organizing Data Comparable

Posted by mayur lalwani
mayur lalwani
992 Points

unable to solve code.where's the error?

The code is perfectly written according to me but I cannot find an error

com/example/BlogPost.java 
package com.example;

import java.util.Date;

public class BlogPost implements Comparable {
  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[] getWords() {
    return mBody.split("\\s+");
  }

  public String getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }

  @Override
  public int compareTo(Object obj){
     BlogPost other = (BlogPost)obj;
    if(equals(other)){
      return 0;
    }
    int dateCmp = mCreationDate.compareTo(other.mCreationDate);
    if(dateCmp == 0){
      return mDescription.comareTo(other.mDescription);
    }
    return dateCmp;
  }


  public String getBody() {
    return mBody;
  }

  public String getCategory() {
    return mCategory;
  }

  public Date getCreationDate() {
    return mCreationDate;
  }
}

1 Answer

Steve Hunter
Steve Hunter
57,712 Points

Hi Mayur,

You're very close! (And you have a typo in your second compareTo() method)

Try this: 

  public int compareTo(Object obj){
    BlogPost bp = (BlogPost) obj;
    if(bp.equals(this)){
      return 0;
    }
    if(this.mCreationDate.before(bp.mCreationDate)){
      return -1; 
    }
    return 1;
  }

We cast obj to a BlogPost called bp. If bp is equal to the current instance, this, return zero. Else decide which comes first, using the before method comparing the mCreationDate of both the bp instance and this instance. If they're equal, we return zero and if one is before the other we return 1 or -1 depending on which order they fall in.

I hope that helps.

Steve.

Steve Hunter
Steve Hunter
57,712 Points

We could use parts of your code to do the same.

If we remove the if statement that looks for equality and compares mDescription - we've done the equals bit already. Then, if we use your other BlogPost instance that you've created you get this:

    public int compareTo(Object obj){
    BlogPost other = (BlogPost) obj;
    if (other.equals(this)){
      return 0;
    }
    int dateCmp = mCreationDate.compareTo(other.mCreationDate); // just return this
    return dateCmp;
    }

That should work. This uses the compareTo() method, rather than the before() method, which is fine. It takes fewer lines of code but adds nothing to the clarity of the output - it isn't user-friendly. You can also return the comparison directly; dateCmp isn't doing anything.

Steve.

mayur lalwani
mayur lalwani
992 Points

Thanks a lot..