General Java Questions I

network monitors will share this interface, but they may have a class heirarchy that is

very different, for example, port monitors may all fork a thread that periodically

checks whereas our control panel interface just asks for the most recent answer;

hardware monitors may ask for their data in real time or over RPC and thus have no

need of inheriting from Thread.

Because they share the same Interface definition, the control panel application does

not need to know if they are polling monitors or real time monitors because, from the

control panel s point of view, it does not matter

...

P.S. by John

Also interfaces make our life (I mean programmers) much easier.

Imagine a big project ( a lot of programmers, many packages, thousands of files): it is

impossible all the time to be aware about particular implementation of some method

in specific class in another package!

Much easier to define interfaces between packages as some kind of bridges or gates

into another package and their functionality, with hidden (for us) implementation. We

just know interface and method names. It is enough to use those methods.

How it is implemented there does no matter... It is working!

Q: Is a static variables value likely to be garbage collected once objects of the

class are no longer pointing to it? Does it destroy itself at any point or must that be

done explicitly?

I have a class with a static variable I create two instances of this class.

In each instance I modify the static variable. Then I destroy the objects(point them to

null), then create another instance of the same class and reference the static

variable.

Answer: No   the static variables are effectively linked to the Class object 

rather than any instances; they will only be garbage collected when the 

Class is garbage collected. This will only happen if the ClassLoader 

which loaded the Class is garbage collected.

Jon Skeet

http://www.pobox.com/~skeet

 Q: I find such function, but in Class class. Is it possible to use it (or something like

this) in another class? Exactly I would like call: super.super.method1();

Answer: No, you can only access methods of your direct ancestor.

The only way to do this is by using reflection:

import java.lang.reflect.*;

Class superduper = this.getClass().

getSuperClass().

getSuperClass();

Method ssMethod = superduper.getMethod("method1",null);

ssMethod.invoke(this,null);

(I didn t check the exact syntax and parameters of the above code.)

However the necessity to skip a hierarchy shows that there is something wrong with

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