Why equals() method must be compatible with compareTo in java ?

Question

Give proper explanation.

I am new in Java but I have knowledge about C programming.

Answer 1

Please go through this following link. Hope this will help you.
http://docs.oracle.com/javase/7/docs/api/java/lang/Comparable.html

Answer 2

CompareTo() method in Java must be compatible with equals method in Java i.e. if two objects are equal via equals method compareTo method must return “0″ for them, failing this may result in some subtle bug when you store those objects in collection class like arraylist in java. For detailed answer check here http://javarevisited.blogspot.in/2011/02/how-to-write-equals-method-in-java.html

Comments

They are not same "abc".equals((String)null) returns false while "abc".compareTo((String)null) == 0 throws a NullPointerException. So they are not always interchangeable even for Strings.