Object is the root-super class of any object in Java. All objects extend this class by default, even if there is no extends-section in signature of class.
Everything in Java is an object.
Object is an ordinary class. It has number of useful methods like equals, hashCode, toString. If any new class require to use these methods or override them it must contain "extends Object" section in it's signature.
List all methods in Object class which are allowed to be extended or overridden