Exception

Checked Exceptions

Classes which directly inherit Throwable except RuntimeExceptions and Errors.

Unchecked Exceptions

Classes which inherit RuntimeExceptions

Handling

Catching

• try

  • Used to specify a block of code which can throw an exception.
  • Must be followed by a catch or finally.
  • Can't be used alone

• catch

  • Block used to handle the error.
  • Must be preceded by try
  • Can't be used alone

Always execute

• finally

Contains the code which must be executed irrespective of whether an exception is handled or not

Throwing

• throw

Used to throw an exception

• throws
  • Used to declare exceptions
  • Doesn't throw error
  • Specifies that an exception may occur in a method
  • Used with method signature

Creating Custom Exceptions

• How to create?

  Create a class WhateverException which extends Exception

• How to return your custom message while throwing exception?

  Pass the message you want to show as a String to the Exception (or super).

• Are custom exceptions checked or unchecked?

  If you want it to be checked, extend Exception. If you want it to be unchecked, extend RuntimeException.

Propagation

Exceptions in main() method

• What happens when main() throws an error?

  Java Runtime terminates the program and print the exception message and stack trace in system console.

• Can throws keyword be used with main()?

  Yes, it can be used. Although, there's no reason for a main method to throw anything. Since, any error will handled by JVM in the same way.

Exceptions raised in common scenarios

• Dependency Injection (cs)
• Throwable (cs)