Throwable

Question

Hi All,
I'm basically new to Java & wanted know why do we need Exception class when already there is throwble. Exception has 4 constructor only & same is present in throwable as well. what is the need of exception class?
Thanks,
Karthik

Answer 1

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You are correct but we can achieve the same by simply extending throwable class in our custom exception class. Something like:
MyException extends Throwable{ }
what is the use in doing MyException extends Exception?
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Perhaps if you read Chapter 11 'Exceptions' in the Java Specification it will make it more clear to you
http://docs.oracle.com/javase/specs/jls/se7/jls7.pdf
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11.1.1 The Kinds of Exceptions
An exception is represented by an instance of the class Throwable (a direct subclass of Object) or one of its subclasses.
Throwable and all its subclasses are, collectively, the exception classes.
Note that a subclass of Throwable must not be generic (§8.1.2).
The classes Exception and Error are direct subclasses of Throwable.
Exception is the superclass of all the exceptions from which ordinary programs
may wish to recover.
Error is the superclass of all the exceptions from which ordinary programs are not
ordinarily expected to recover.
Error and all its subclasses are, collectively, the error classes.
The class Error is a separate subclass of Throwable, distinct from Exception in the class
hierarchy, to allow programs to use the idiom "} catch (Exception e) {" (§11.2.3)
to catch all exceptions from which recovery may be possible without catching errors from
which recovery is typically not possible.
The class RuntimeException is a direct subclass of Exception.
RuntimeException is the superclass of all the exceptions which may be thrown
for many reasons during expression evaluation, but from which recovery may still
be possible.
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Note the next to last paragraph that starts with 'The class Error is a separate subclass of Throwable . . .'.
That paragraph tells you EXACTLY why there is both an Error class and an Exception class.
And, because both Error and Exception have a lot in common that commonality is expressed in
the superclass Throwable.
As that paragraph says programs will use "} catch (Exception e) {" to catch and handle problems
that you may be able to recover from.
If you need to better identify and deal with your own problems you would extend the Exception
class since your own problems will be exceptions, not 'Errors'.
Sure, you could write your own classes to extend from Throwable but everything you did would be
non-standard and would serve no purpose at all other than just 'being different'.