Q:

Interfaces are not part of Object hierarchy in Java. Why ? Do they belong to some hierarchy?

I am preparing for an OCJP. I came across this statement in Kathy Sierra's book.

Interfaces are not part of Object hierarchy in Java

I am just curious and want to know why ?

A:

In order to precise things a bit: 
An interface is not part of the object hierarchy, meaning that an interface which does not extend another one has no supertype. 
However, an instance typed as an interface is always an Object, otherwise you would not be able to write things like: 
interface MyInterface { //no supertype.
}
MyInterface var = new MyInterface(){};
var.toString(); //toString method is defined on Object class.

