Custom Exception class - extends from Exception or Thowable? [duplicate]

Answer 1

Fundamentally you should extends Exception class as you are creating Custom Exception. Exception and Error both extends Throwable, It really does not make sense extending Throwable.

Answer 2

Throwable is a class for all the bad situations, which can arise: Errors & Exceptions.

Error is something, you can't handle at all: OutOfMemoryError, VirtualMachineError, etc.

Exception is for exceptional cases.

Exceptions come in 2 flavours:

1. RuntimeExceptions.

   These ones, you are not aware of: NullPointerException, ClassCastException, etc.

2. Checked exceptions.

   These are the exceptions, which your code is aware of and should be explicitely catched (... throws MyException): IOExceptions, etc.

If you want the users of your code, to explicitely handle some exceptional situations, it would be good to just extend Exception, not the RuntimeException. There's no need to extend Throwable.

Answer 3

Throwable is the super class of Error & Exception.

Like Exception, Error too, can be thrown & handled.

But it is not advisable, according to the following doc:

You are not required to catch Error objects or Error subtypes. You can also throw an Error yourself (although other than AssertionError you probably won't ever want to), and you can catch one, but again, you probably won't. What, for example, would you actually do if you got an OutOfMemoryError?

Keeping this concept in mind, I would suggest to extend Throwable if you want to throw and/or catch Exception & Error both. Extend Exception if you want to throw and/or catch Exception only.