Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

Java Java Data Structures Organizing Data Comparable

Timmie Nilsson
Timmie Nilsson
4,463 Points

A question about equals

Hi in this if I make a equals(other)

But I don't understad what the equals compare 'other' to?

Usually I see 'example.equals(hamster)' I googles it but all example shows the same as mine... How does this works?

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 int compareTo(Object obj){
    BlogPost other = (BlogPost) obj;
    if(equals(other)){
      return 0;
    }
    return 1;
  }

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

  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

Hi Timmie,

The compareTo method is comparing the instance of BlogPost that compareTo is being called on, to the argument passed in.

So, to use compareTo, you need to create an instance of BlogPost first. It is that instance which is compared to the obj.

You can make this clearer by using the this keyword to indicate you are using the instance of the class:

  public int compareTo(Object obj){
    if(this.equals((BlogPost) obj)){
      return 0;
    }
    return 1;
  }

Make sense?

Steve.

Timmie Nilsson
Timmie Nilsson
4,463 Points

Well it makes sense but a little confusion :)