Exception in the case of Overriding

Question

As we know that in the case if method overriding If child class method throws some checked exception then compulsory parent class method should throw same checked exception or its parent class exception otherwise we will get compile error. But there is no rule on un-checked exception.

But if assume that Java allows parent class method to have checked exception which is child to the child class method checked exception.

Can some one please why this is not allowed in the Java.

---

Let put the question in a different way :

you have class A -

class A {

    public void doStuff() throws SQLException {

    }
}

and class B extends A -

class B extends A {

    public void doStuff() throws Exception {

    }
}

It will throw exception during compilation because of violation of the method's contract.

Assume that the Java would allows this then what would be the consequences ?

Answer 1

I suppose you are asking why I cannot do this:

class Parent {
    void doStuff() throws FileNotFoundException {

    }
}

class Child extends Parent {
    @Override
    void doStuff() throws IOException {

    }
}

This is simple, what happens when I do:

final Parent parent = new Child();

try {
    parent.doStuff();
} catch (FileNotFoundException e) {
    e.printStackTrace();
}

And the Child decides to throw a, say SocketException?

I, correctly, try and catch FileNotFoundException from the call parent.doStuff but this will not catch the SocketException.

How I have an uncaught checked exception. This is not allowed.

If I specifically try and catch SocketException this will result in a compiler error as SocketException is not declared as thrown from Parent.doStuff.

The only way to solve this in the general case would be to always catch Exception as any child class can declare that it throws a more general type and bypass my catch. This is obviously not ideal.