Default class that is extended by all classes in java

Question

Is there any Default Class that is extended by all the classes by default in Java?

Example: If I have a simple class like:

Class A {
  String a;
}

Is this class extending a class by default?

Answer 1

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");
} 

Answer 2

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