Inheritance is comparable to how you inherited traits such as your height, eyes, hair, DNA, and allergies from your parents. They in turn inherited some of their traits from their parents, that is, your grandparents. Inheritance of such tratis basically keeps going backwards in time till the very first people who populated Earth, say Adam and Eve, the root of your ancestorial hierarchy.
Similarly, every class hierarchy has a root class. All the class hierarchies in
Java have the same class as their root class: the Object class. When the extends
clause is absent, an implicit extends clause inheriting the Object class is
provided by Java.
In Java, the Object class is the root of class hierarchy. In other words,
the Object class is the superclass of all classes in Java.
The Object class is special because it is the only class in Java that does not
inherit any other class.
The Object class defines the following methods, which means that they are
available in every object.
The clone() method creates a clone of the object is being invoked against.
The equals() method determines whether one object is equal to another object.
It compares two objects and returns true if both are same, otherwise it
returns false.
The finalize() method is invoked by the Java Virtual Machine (JVM) before
the object is destroyed.
The getClass() returns an object which represents the class of an object
at runtime. This method is part of the reflection API, which allows you to
dynamically load classes, create instances, and invoke methods.
The hashCode() method returns the hash code of the object.
When you invoke the notify() method it resumes execution of a thread
waiting for the object.
Invoking the notifyAll() resumes the execution of all the threads waiting
on the object.
You have already seen the toString() method. It returns a string that
describes the object.
In order to wait for an object to signal from another thread, you invoke
the wait() method.
The methods getClass(), notify(), notifyAll(), and wait() are declared
as final. You cannot override them.