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Java

Posted by Rey Adronico Baguio
Rey Adronico Baguio
13,672 Points

Comparable Treet question

I didn't understand how Craig was able to order an array of Treets. Here's what I understood:

  1. He overrode the compareTo() method from Comparables.

  2. He then instantiated a new Treet and typecasted the required Object "obj" as a Treet.

  3. He then wrote this code and this is where I get lost:

if (equals(others)) { return 0; }

I don't quite understand what that actually means considering equals is a method (but it's not attached to an object in this case). If it's compared to obj, why do we have to compare it to "others" considering we just instantiated others using obj.

Lastly, Can we call the compareTo() method (in class Comparable) inside a method declaration of compareTo (in class Treet) as Craig did?

Enrique Munguía
Enrique Munguía
14,311 Points

Can you provide the code snippet please?

Rey Adronico Baguio
Rey Adronico Baguio
13,672 Points

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

1 Answer

piyush arora
piyush arora
5,735 Points

Hi Rey,

if(equals(other))...This simply means this.equals(other) i.e the current Treet object is compared to object reference passed i.e obj typecasted to other (Treet). If both objects are equal i.e we are talking about the same object, 0 is returned.

int dateCmp = mCreationDate.compareTo(other.mCreationDate)

This is where comparison happens based on the creation date of the treet...mCreationDate(Date Object implements Comparable Interface) to other.mCreationDate(other->Treet instance has property mCreationDate) ...If both treets were created on the same date i.e datecmp==0 then comparison is made on the description i.e 

mDescription.compareTo(other.mDescription)

If this also same then the we are about the same treet...0 is returned!!

Hope this helps!!