Why does Java allow this?

Hello Folks
Today I saw the following code in an exam about Java programming:
interface I {
public final static double var = 32.0;
class A implements I {
double var = 15;
}How can Java allow such a construct? I overload a variable that is public, static and final and replace it with an instance variable that is protected. In my opinion the compiler should reject that, I mean it does it when I try the same with a method. Why is it allowed with variables?
Regards
Der Hinterwaeldler

The declaration of the variable var in class A does not override the declaration in the interface I, it only hides it.
Methods are different because methods can be overridden. Static and final methods are an exception, they can't be overridden so trying to do it is a compile time error.
See also http://java.sun.com/developer/TechTips/2000/tt1010.html#tip2

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I've been curious about this topic for a while, but I haven't ever looked into this to any depth. I also posted this to stackoverflow but haven't gotten any solid responses so far:
http://stackoverflow.com/questions/1107991/why-does-java-have-such-a-large-footprint
Java - or at least Sun's Hotspot JVM - has long had a reputation for having a very large memory footprint. What exactly is it about the JVM that gives it this reputation? I'd be interested in a detailed breakdown: how much memory goes to the runtime? (The JIT? The GC/memory management? The classloader?) Anything related to "auxiliary" APIs like JNI/JVMTI? The standard libraries? (Which parts get how much?) Any other major components?
I realize that this may not be straightforward to answer without a concrete application plus VM configuration, so just to narrow things down at least somewhat: I'm primarily interested in default/typical VM configurations, and in a baseline console "Hello world" app as well as any real-world desktop or server app. (I'm suspecting that a substantial part of the JVM's footprint is largely independent of the app itself, and it is in this part that I'd like to zoom in, ideally.)
I have a couple of other closely related questions:
Other similar technology, such as .NET/mono, don't exhibit nearly the same footprint. Why is this the case?
I've read somewhere on the intarwebs that a large portion of the footprint is due simply to the size of the standard libraries. If this is the case, then why is so much of the standard libraries being loaded up front?
Are there any efforts (JSRs, whatever) to tame the memory footprint? The closest thing I've come across is a project to reduce the on-disk footprint of the JVM [1] and to modularize the standard library [2].
I'm sure that the footprint has varied over the past decade or so with every new version of Java. Are there any specific numbers/charts chronicling precisely how the JVM's footprint has changed?
[1] http://blogs.sun.com/jtc/entry/reduced_footprint_java_se_bringing
[2] http://blogs.sun.com/theplanetarium/entry/project_jigsaw_modularizing_jdk_7

yangzhang wrote:
I've been curious about this topic for a while, but I haven't ever looked into this to any depth. I also posted this to stackoverflow but haven't gotten any solid responses so far:
http://stackoverflow.com/questions/1107991/why-does-java-have-such-a-large-footprint
Java - or at least Sun's Hotspot JVM - has long had a reputation for having a very large memory footprint. What exactly is it about the JVM that gives it this reputation? I'd be interested in a detailed breakdown: how much memory goes to the runtime? (The JIT? The GC/memory management? The classloader?) Anything related to "auxiliary" APIs like JNI/JVMTI? The standard libraries? (Which parts get how much?) Any other major components?
Presumably versus some other VM. I would suppose the fact that much of the VM is written in java has something to do with it.
I realize that this may not be straightforward to answer without a concrete application plus VM configuration, so just to narrow things down at least somewhat: I'm primarily interested in default/typical VM configurations, and in a baseline console "Hello world" app as well as any real-world desktop or server app. (I'm suspecting that a substantial part of the JVM's footprint is largely independent of the app itself, and it is in this part that I'd like to zoom in, ideally.)
I have a couple of other closely related questions:
Other similar technology, such as .NET/mono, don't exhibit nearly the same footprint. Why is this the case?
Not sure I agree with that. What size do you see with a .Net app that uses 3.0/3.5?
I've read somewhere on the intarwebs that a large portion of the footprint is due simply to the size of the standard libraries. If this is the case, then why is so much of the standard libraries being loaded up front?
Good question. There is a feature that allows multiple VMs to use the same memory footprint version of the loaded libraries. That is a new feature and it isn't clear to me if it covers the entire API. I do not know if that is dynamically built.

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Solved!
Go to Solution.

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Message Edited by jcarmody on 03-27-2009 11:58 AM
Jim
You're entirely bonkers. But I'll tell you a secret. All the best people are. ~ Alice
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Why does LabVIEW allow me to have 2 controls with the same name in the same VI? It seems like this only increases the chances of confusion. Especially when someone is just looking at a block diagram (or documentation of a block diagram).
No other programming language that I know of allows this. I realize that uniqueness of name is not as critical in LabVIEW as it is in any text based language. For example, in a text based language, if I had 2 variables called abc and I wrote a statement
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Message Edited by S G on 12-18-2007 03:38 PM
S G
Certified LabVIEW Architect, Certified TestStand Developer, Certified Professional Instructor
Attachments:
Trial1.JPG ‏21 KB

I know when you copy and paste a control or indicator, LabVIEW automatically increments the label. But since you can hide the label, and show or hide the caption, there must be another mechanism that LabVIEW uses to keep track of all the controls. I thought I remember back in the "old days" (ver 6 or 6i) LabVIEW would give you an error if you tried to make two controls with the same name. Perhaps that was LabWindows/CVI.
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Interestingly, this array of references grows from the beginning. That is, any new control or indicator is put at index 0, not the end of the array.
B-)
Message Edited by LabViewGuruWannabe on 12-18-2007 08:45 PM
Attachments:
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Date: Wed, 18 Dec 2013 08:24:05 -0800
From: [email protected]
To: [email protected]
Subject: Why does Illustrator open this file incorrect (coloured polygon becomes uncoloured)
    Re: Why does Illustrator open this file incorrect (coloured polygon becomes uncoloured)
    created by tonyharmer in Illustrator - View the full discussion
Hi Patrick
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