1.	Checked exceptions are exceptions that must be 
declared in the throws clause of a method. A checked 
exception indicates an expected problem that can occur 
during normal system operation. Checked exceptions must be 
2.	Unchecked exceptions are exceptions that do not 
need to be declared in a throws clause. An unchecked 
exception indicates an unexpected problem that is probably 
due to a bug in the code. The most common example is a 
NullPointerException.They don't have to be caught or 
declared thrown.
3.	Checked exceptions in Java extend the 
java.lang.Exception class. Unchecked exceptions extend the 
java.lang.RuntimeException. 

checked Exceptions must be dealt with in either a try/catch
block or by
declaring a "throws" in a method. Unchecked exceptions
normally are
Runtime exceptions like NullPointerException or
ClassCastException.

A simple rule of thumb: If it's an exception you can
possibly deal with
(continue to run the program using some alternative code),
use checked
exceptions. For exceptions that should never happen (if they
do, it's a
bug), use unchecked (Runtime) exceptions which will come up
to the
surface and displayed to the user. Like this you assure that
if there's
a bug, it will show up eventually and can be fixed, and you
don't run
the risk of catching an exception and forgetting to deal
with it (f.i.
empty catch block).