Default class that is extended by all classes in java

java.lang.Object class is superclass of all classes.

Class Object is the root of the class hierarchy. Every class has Object as a superclass. All objects, including arrays, implement the methods of this class.

You can test it :

A a = new A();
if(a instanceof Object){
  System.out.println("Object is superclass of all classes");
} 

In Java, everything (apart from the plain old data types; int, boolean, double etc.) is implicitly derived from java.lang.Object.

In particular, the class contains useful functions such as lock() and notify() which are used in thread synchronisation.

For a full list, see http://docs.oracle.com/javase/6/docs/api/java/lang/Object.html

Yes it is and it is extending Object class.

Object is root class of all java classes.