Method Overriding

[Soumya Ranjan Mohanty]

A overridden method in a subclass cannot throw Broader exception than the method in its Superclass ok, my question is can it throw the same exception as in the Super class??

class OverExc {

public void meth() throws FileNotFoundException {
System.out.println("Inside OverExc");
}
}

class OverExc1 extends OverExc {

public void meth() throws FileNotFoundException {
System.out.println("Inside OverExc1");
}
public void meth1() {
System.out.println("Meth1 Inside OverExc1");
}

Is it Correct?

[pete stein]

Soumya Ranjan Mohanty wrote:A overridden method in a subclass cannot throw Broader exception than the method in its Superclass ok, my question is can it throw the same exception as in the Super class??

Broader means >. Same means =. and since = is not >, one anser is "Yes". Another answer is "try it and see".

[Seetharaman Venkatasamy]

Soumya Ranjan Mohanty wrote:A overridden method in a subclass cannot throw Broader exception than the method in its Superclass ok,

It is not applicable in case of the Exception is Unchecked(Runtime) Exception.Of-course you should not throws Runtime Exception from method signature

[Devaka Cooray]

Soumya, please UseCodeTags and do NOT use unnecessary font colors and sizes.

[Himanshu Gupta]

Soumya Ranjan Mohanty wrote:A overridden method in a subclass cannot throw Broader exception than the method in its Superclass ok, my question is can it throw the same exception as in the Super class??

class OverExc {

public void meth() throws FileNotFoundException {
System.out.println("Inside OverExc");
}
}

class OverExc1 extends OverExc {

public void meth() throws FileNotFoundException {
System.out.println("Inside OverExc1");
}
public void meth1() {
System.out.println("Meth1 Inside OverExc1");
}

Is it Correct?

The overridden method can throw the same Exception or any other Exception which is its subtypes. You cannot throw an Exception that is broader than the declared one and YES as specified above this applies only for the checked Exceptions.

You can read this if it still not clear.

HTH

[Jim Hoglund]

In an overriding method, the rule of throwing the same or a narrower exception must
be obeyed for all exceptions, even unchecked exceptions. Although the compiler will
not flag the error, it is not okay to thow a broader exception. Existing code may not
handle the broader exception properly.

Jim ... ...

[Mike Simmons]

No. Unchecked exceptions are completely unaffected by this rule, as Himanshu Gupta stated.

Since we have people posting conflicting information, rather than simply making another bald assertion, it might be helpful to post a simple demonstration:

public class CheckedVsUnchecked {
  public static void main(String... args) {
    new Bar().method();
  }
}

class Foo {
  void method() throws NullPointerException {
    throw new NullPointerException();
  }
}

class Bar extends Foo {
  void method() throws RuntimeException {
    throw new RuntimeException();
  }
}

[Rob Spoor]

What Jim meant is that although it is legal for the compiler it does violate the Liskov substitution principle - calling code will not expect these new exceptions and therefore will never handle them correctly. But in the case of RuntimeException this isn't always a big problem since most RuntimeExceptions indicate a programmer mistake. IllegalArgumentException, NullPointerException, NoSuchElementException, IllegalFormatException, InputMismatchException - all can be prevented by proper checks.

[Campbell Ritchie]

Another way to say what Rob says is that declaring unchecked Exceptions does violate the Liskov Substitution Principle, but the compiler has no way of verifying unchecked Exceptions.