Java questions

[NepaliGuy]

1. Can subclass inherit the static methods?

2. Can you overide the static menthods?

[Chris]

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NepaliGuy wrote:

1. Can subclass inherit the static methods?

2. Can you overide the static menthods?

Hi,
Both of these are impossible. Ignoring reflection, the only way to
call a static method is if you already know the classname at compile
time. If you already know the classname, it makes no sense to inherit
a static method, since it would never get called anyway. I'm aware
that you can call static methods through an instance of a class, but
this is considered bad. Having just run a quick test, I realize why:
the static method called is selected by the declared type of the
variable, not the actual type of the object! For example, given
classes A and B, where B extends A, and where both define a static
method x(), the following code:

A a = new B();
a.x();

actually ends up calling A.x(), since the runtime type of a is
ignored.

The fact is, there is no practical use for inheriting or overriding
static methods, since there is no way for a subclass's version to be
called polymorphically anyway. You can define a new static method of
the same name in a class that just happens to be a subclass, though I
assume this doesn't count as overriding.

If you do happen to be using reflection, and need a class (whose name
is to be determined at runtime) to have a certain static method, your
only option is to write this requirement in documentation and hope
the client obeys it.

- --
Chris
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[NepaliGuy]

Hey thanks Chris. It was great explaination. I like the way you explained
the philosphy behind the reason.

"Chris" <ch*******@hotm ail.com> wrote in message
news:rW******** ************@ne ws0.telusplanet .net...

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NepaliGuy wrote:

1. Can subclass inherit the static methods?

2. Can you overide the static menthods?

Hi,
Both of these are impossible. Ignoring reflection, the only way to
call a static method is if you already know the classname at compile
time. If you already know the classname, it makes no sense to inherit
a static method, since it would never get called anyway. I'm aware
that you can call static methods through an instance of a class, but
this is considered bad. Having just run a quick test, I realize why:
the static method called is selected by the declared type of the
variable, not the actual type of the object! For example, given
classes A and B, where B extends A, and where both define a static
method x(), the following code:

A a = new B();
a.x();

actually ends up calling A.x(), since the runtime type of a is
ignored.

The fact is, there is no practical use for inheriting or overriding
static methods, since there is no way for a subclass's version to be
called polymorphically anyway. You can define a new static method of
the same name in a class that just happens to be a subclass, though I
assume this doesn't count as overriding.

If you do happen to be using reflection, and need a class (whose name
is to be determined at runtime) to have a certain static method, your
only option is to write this requirement in documentation and hope
the client obeys it.

- --
Chris
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