unpredictable error come at run time that is called exception. compile time error called checked and run time error that is called unchecked.

Unusual behavior of program called exception Compile time exception called checked Runtime exception called unchecked

Follow the link below.http://www.c-sharpcorner.com/UploadFile/9a9e6f/exception-propagation-in-java/

http://javarevisited.blogspot.in/2011/12/checked-vs-unchecked-exception-in-java.html

Exception is the deviation from the ordinary program flow or operations.Checked Exception are those which are checked at compile time i.e. there is a way given to handle the exception .Example - When you use file reader or buffered Reader , you use them in try and catch and exceptions that are checked are I/O exception , file not found etc. If you don't use try catch it gives error to use it.Unchecked Exception re those which are not handled at compile time and they are thrown at run time. Example - Null pointer Exception , ArrayIndexOutOfBound Exception etc.