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Java

Ian Z
Ian Z
14,584 Points
Posted by Ian Z
Ian Z
14,584 Points

Java Data Structures challenge comparable uses if(equals()) how does this work

In this step, cast the Object passed to the compareTo method to a com.example.BlogPost. Check for equality first, if they are equal return 0. Leave the default return of 1 in place for this step.

the code is 

    @Override
  public int compareTo(Object obj){
    BlogPost bp = (BlogPost)obj;
    if(equals(bp)){
      return 0;
    }
    return 1;
  }

dosent equals(bp) need to be called on something? what is equals comparing bp to?

Steve Hunter
Steve Hunter
57,712 Points

Have you got the link to that challenge? I agree with you that it looks odd like that.

Steve.

Ryan Jin
Ryan Jin
15,337 Points
Ryan Jin
Ryan Jin
15,337 Points

You use this.equals, like this

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

8 Answers

Steve Hunter
Steve Hunter
57,712 Points

Hi Ian,

Have a look at this post which might help you figure out what's required.

I've got as far as:

  public int compareTo(Object obj){
    if(obj instanceof BlogPost){
      BlogPost bp = (BlogPost) obj;
      return 0;
    }
    return 1; 
  }

Steve.

Ian Z
Ian Z
14,584 Points
Ian Z
Ian Z
14,584 Points

Hey Steve, thanks for help, i wasnt very clear on this sorry, i just linked code because it had example of equals() without a . before it and id never seen that before and was wondering what it was called on

amathiaitishar
amathiaitishar
13,229 Points
amathiaitishar
amathiaitishar
13,229 Points

The java course is full of strange challenges, it never stops surprising me ...Why?!!!

Neil Gordon
Neil Gordon
8,823 Points
Neil Gordon
Neil Gordon
8,823 Points

this is what worked for me on the challenge 

public int compareTo(Object obj) {
    if(equals(obj)) {
      return 0;
    }
    return 1; 
  }
Rulon Taylor
Rulon Taylor
2,762 Points

Hi Neil,

Doesn't the code you posted simply compare obj to obj? Thus, it should always evaluate as true and return 0. Right?

I'm thinking the code needs to be more like

BlogPost bp = (BlogPost) obj if(equals(obj)) { return 0; } return 1; }

What am I missing?

Dawid Dlubek
Dawid Dlubek
1,583 Points
Dawid Dlubek
Dawid Dlubek
1,583 Points

This worked:

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

Craig Dennis
STAFF
Craig Dennis
Treehouse Teacher
Craig Dennis
Craig Dennis
Treehouse Teacher

equals is a method also inherited from java.lang.Object. All Objects have an equals method, so this is basically comparing the instance to the passed in value, in this case the BlogPost instance bp.

That make sense?

Ian Z
Ian Z
14,584 Points
Ian Z
Ian Z
14,584 Points

Yes thanks very much, so its kinda like this.equals

kristoffer tølbøll
kristoffer tølbøll
1,337 Points

Makes no sense...

Steve Hunter
Steve Hunter
57,712 Points

Hi Kristoffer,

What are you having problems with?

Steve.

kristoffer tølbøll
kristoffer tølbøll
1,337 Points
kristoffer tølbøll
kristoffer tølbøll
1,337 Points

Hello Steve, i was not trying to be rude. Sorry if i sounded that way. I read in the javadoc, athat if you implement the comprable class you also have to put the class name in <>.

like this

public Class A implements comparable <A>

i did not see this syntax in the challenge i'm i missing something?

i Also have a hard time understanding the compareTo method could you elaborate

Darwin Palma
Darwin Palma
3,430 Points
Darwin Palma
Darwin Palma
3,430 Points

It worked for me in the challenge.

public int compareTo(Object obj){
    if(equals(obj)){
      BlogPost blogPost = (BlogPost)obj;
      return 0;
    }
    return 1;
}
Mike Stanton
PLUS
Mike Stanton
Courses Plus Student 3,250 Points
Mike Stanton
Mike Stanton
Courses Plus Student 3,250 Points

//Create a new method overriding the existing class method 'compareTo' @Override public int compareTo(Object obj){ //Create a new BlogPost instance object (newBlogPost) for Comparing: BlogPost newBlogPost = (BlogPost) obj; //Here is where we are casting the object passed into the method to a BlogPost object. //Check for equality of those two Objects: if(equals(obj){ //This is saying: if the class Object BlogPost == the casted Object obj return 0. In this case, because we cast the object to a BlogPost object, then we should get 0 return 0; } return 1; }