I want to know why the .compareTo() is in the Comparable interface while a method like .equals is in the Object class. To me, it seems arbitrary why a method like .compareTo() is not in the Object class already.To use .compareTo(), you implement the Comparable interface and implement the .compareTo() method for your purposes. For the .equals() method, you simply override the method in your class, since all classes inherit from the Object class. My question is why is a method like .compareTo() in an interface that you implement rather than in a class like Object? Likewise, why is the .equals() method in the class Object and not in some interface to be implemented?
Why is .compareTo() in an interface while .equals() is in a class in Java?
java;language design;interfaces
Not all objects can be compared, but all objects can be checked for equality. If nothing else, one can see if two objects exist at the same location in memory (reference equality).What does it mean to compareTo() on two Thread objects? How is one thread greater than another? How do you compare two ArrayList<T>s?The Object contract applies to all Java classes. If even one class cannot be compared to other instances of its own class, then Object cannot require it to be part of the interface.Joshua Bloch uses the key words natural ordering when explaining why a class might want to implement Comparable. Not every class has a natural ordering as I mentioned in my examples above, so not every class should implement Comparable nor should Object have the compareTo method....the compareTo method is not declared in Object. ... It is  similar in character to Object's equals method, except that it  permits order comparisons in addition to simple equality comparisons,  and it is generic. By implementing Comparable, a class indicates  that its instances have a natural ordering.Effective Java, Second Edition: Joshua Bloch. Item 12, Page 62. Ellipses remove references to other chapters and code examples.For cases where you do want to impose an ordering on a non-Comparable class that does not have a natural ordering, you can always supply a Comparator instance to help sort it.