Subject: Var access question... 2006-11-01 - By Mike New
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> Hi list, I'm wondering if it's a good practice to access fields (in
> the same class) through its names and not by its accessors, e.g.
>
> public class ComplexNumber {
> private double U;
> private double V;
>
> // constructor deleted
>
> public double real() {
> return U;
> }
>
> public double imaginary() {
> return V;
> }
>
> public double magnitude() {
> return (Math.sqrt(Math.pow(U, 2) + Math.pow(V, 2)));
> // access here must be U or real(), same with V
> }
>
> public double arg() throws ArithmeticException {
> return (Math.atan(V / U));
> // access here must be U or real(), same with V
> }
>
> public ComplexNumber times(ComplexNumber Z) {
> return new ComplexNumber(U * Z.U - V * Z.V, U * Z.V + V * Z.U);
> }
> }
>
> I think it accomplish to OOP rules (encapsulation), the object itself
> manages its state interacting with its fields and no other can change
> their
> properties, but I've seen many samples that use getters methods to access
> values, I don't know why...any clue ???
Providing a getter has the advantage that you can change the behaviour
without changing the class' API. So getMyObject() might at first look
like this:
// myObject should be initialized already
public MyObject getMyObject() {
return myObject;
}
but later you might want to lazily initialize it, so you could change it
to this:
public MyObject getMyObject() {
if(myObject == null)
{
myObject = initializeMyObject();
}
return myObject;
}
Giving other objects direct access to myObject would make the above change
much more difficult, and you'd HAVE to initialize it early on, such as in
the constructor.
I have several examples where I might not need an object which is
expensive to initialize (i.e. a file specified by a URL), so I want to
populate the variable only when necessary.
Other arguments are that encapsulation is just cleaner, making the class
easier to use and understand. The value of this shouldn't be
underestimated, IMO.
Mike
>
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