Ask HN: Why should variable shadowing be allowed?

In java I like using variable shadowing in constructors, that is, I write something like:

  public SomeObject(String aField) {
    this.aField = aField;
  }

I think this promotes clarity for the user of the code, although you can possibly make the mistake of writing

  aField = aField;

but if you declare aField as final, the compiler will give you an error if you make that mistake.