02. Exceptions

1.What is Exception Handling?

Exception Handling is a mechanism to handle runtime errors. It is mainly used to handle checked exceptions.

2.What is difference between Checked Exception and Unchecked Exception?

a)Checked Exception

The classes that extend Throwable class except RuntimeException and Error are known as checked exceptions e.g.IOException,SQLException etc. Checked exceptions are checked at compile-time.

b)Unchecked Exception

The classes that extend RuntimeException are known as unchecked exceptions e.g. ArithmeticException,NullPointerException etc. Unchecked exceptions are not checked at compile-time.

3.What is the base class for Error and Exception?

Throwable.

4.Is it necessary that each try block must be followed by a catch block?

It is not necessary that each try block must be followed by a catch block. It should be followed by either a catch block OR a finally block. And whatever exceptions are likely to be thrown should be declared in the throws clause of the method.

5.What is finally block?

• finally block is a block that is always executed

Can finally block be used without catch?

• Yes, by try block. finally must be followed by either try or catch

6.Is there any case when finally will not be executed?

finally block will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort)

7. What is difference between throw and throws?

throw keyword	throws keyword
1)throw is used to explicitly throw an exception.	throws is used to declare an exception.
2)checked exceptions can not be propagated with throw only.	checked exception can be propagated with throws.
3)throw is followed by an instance.	throws is followed by class.
4)throw is used within the method.	throws is used with the method signature.
5)You cannot throw multiple exception	You can declare multiple exception e.g. public void method()throws IOException,SQLException.

8.Can an exception be re thrown?

Yes.

9.Can subclass overriding method declare an exception if parent class method doesn't throw an exception ?

Yes but only unchecked exception not checked.

 

10. What is exception propagation?

Forwarding the exception object to the invoking method is known as exception propagation.