Re: catching exceptions in subclass' constructor?

Lew <>
Mon, 01 Sep 2008 08:28:53 -0400
bugbear wrote:

(in these examples my Exceptions are chosen arbitrarily
from those in java.lang)

Consider a class 'A'

class A {
    public A(int i) throws NoSuchFieldException {

It (for reasons all its own) can throw an exception.

Now consider a sub-class 'B', that extends 'A'.

I would like to give it 2 constructors, one a simple
"clone" of the 'A' constructor, and a parameterless
constructor. I want this because in my real
app 'B' has many subclasses.

If a parameterless constructor that throws
no exceptions can be managed, I won't need to declare
a constructor at all in the (many) sub classes,
which will be helpful to me.

The first constructor is trivial.

class B extends A {
    public B(int i) throws NoSuchFieldException {

Now, since I am going to (carefully) provide
a valid default argument in the B() constructor,
I do not want it to throw a checked exception,
so I map" it to a runtime exception.

So I tried:

   public B() {
        try {
        } catch(NoSuchFieldException e) {
            throw new IllegalStateException(e);

but the compiler says:

" call to this must be first statement in constructor"

I would welcome advice on how to achieve my goal (a parameterless
constructor for B that does not throw an exception).

Favor composition over inheritance.
- Bloch, /Effective Java/ 2nd ed., Item 16.


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