Question

As we know if any error or any unchecked exception occurs then our program will halt, then what are the differences between those?

Answer 1

From the Error Javadoc:

An Error is a subclass of Throwable
that indicates serious problems that a
reasonable application should not try
to catch. Most such errors are
abnormal conditions. The ThreadDeath
error, though a “normal” condition, is
also a subclass of Error because most
applications should not try to catch
it.

Versus the Exception Javadoc

The class Exception and its subclasses
are a form of Throwable that indicates
conditions that a reasonable
application might want to catch.

So, even though an unchecked exception is not required to be caught, you may want to. An error, you don’t want to catch.