Category Archives: Computers

Posts on computer science and the web, rants about OS:es, Window Managers, and the like.

Computers

Iterating a list, and deleting from it, Java vs .NET

Or how I came to realize I could live a life time without .NET and be just as happy.

I’m just fresh from having tried to iterate a list… and delete items from it while iterating.  In .NET with C#.

It turns out a statement like:

void deleteFromList(IList<X> list) {
     foreach (X x in list) {
        if (x.DeleteMe) {
            list.Remove(x);
        }
    }
}

Will throw an InvalidOperationException stating you cannot perform a foreach and delete at the same time.  This is actually not that big of a surprise, or it shouldn’t be…  the same happens in Java if you delete and iterate at the same time.

This is how I would have done this in Java:

void deleteFromList(List<X> list) {
     Iterator<X> itr = list.iterator();
     while (itr.hasNext()) {
	X x = itr.next();
        if (x.DeleteMe) {
            itr.remove();
        }
    }
}

It’s simple, clean and it does not throw exceptions. If you believe the code may be run asynchronously, slap on a “synchronized” and you’re home safe.

So, how to do this with .NET?  Well, you can’t use Enumerators (which are the .NET “equivalent” of iterators), they don’t have a remove method.  Further worse, if you are unlucky enough to run version 1.1 your only option seems to be some unholy concoction like:

void deleteFromList(IList<X> list) {
    IList<X> toBeDeleted = new List<X>();

    foreach (X x in list) {
        if (x.DeleteMe) {
            toBeDeleted.Add(x);
        }
    }

    foreach (X x in toBeDeleted) {
        list.Remove(x);
    }
}

Don’t even start a conversation on synchronization with this mixup.  Anyway, those who are “lucky” enough to code .NET 2.0 can do something like:

myList.RemoveAll(delegate(X x) { return x.DeleteMe; });

Now, if you’d like to base the “DeleteMe” calculation on some external paramter like input to the deleteFromList method or if you’d like to do more than just delete x you’ll have to experiment, it’s probably possible… with a solution like the double lists above perhaps?

Regardless.  Someone said it was old news to be a Java programmer, I can only guess because of the lower hour wastage when you program Java systems, which in turn means lower bills to the clients and finally lower wages to the programmers.

It costs to be on top…

Computers

Moblock traffic blocker

Moblock (moblock-deb) is a so called traffic blocker. It prevents connections from certain IP numbers (defined in block lists) to gain access to your computer. The whole purpose is that the blocked IP numbers usually belongs to this or that organization that wishes to find out more about your Internet habits and other information they have no reason to get their noses into.

Moblock has a big brother called Peerguardian by Phoenixlabs but development on this program seems to have been discontinued, and unfortunately at a stage where the program doesn’t work (at least for me it doesn’t). I am also sure there are some Windows variants of an IP-blocker (I’m guessing Bluetack is the right place to go).

Installing Moblock on Ubuntu turns out to be a very simple affair. Mainly do two things: Add moblock’s repository to your repository list, and run an apt-get command. (Here’s an even better instruction for installing Moblock on Ubuntu).

The installation takes care of setting up cron-jobs to update your block lists every day, installs moblock as a service started every time the machine is started, and makes the first download, after which the program (or in fact, demon) is started and you are safe.

The above link is a very good instruction on installing moblock, and it even have instructions on how to perform some simple troubleshooting.

If you run linux I suggest you take a look at moblock’s home page, or you can check out it’s project page on sourceforge.

Computers

BasKet Note Pads – note-taking application

BasKet is a very nice application I just stumbled across. It is a kind of OneNote for Linux.  In Ubuntu (probably Debian and others as well) it can be managed as a regular package.

I’m using it mostly when writing and ordering ideas and the like, but I can see myself doing much more with it…. once I’ve made sure it’s stable enough. Let me get back on that with a more proper review later.

Computers

How to add a body on load function with Javascript

This is an article on how to add a javascript function that will be run when a web page has loaded. We begin by defining a function for running after a page (or actually window) has been loaded:

function bodyOnLoad() {
  ..
  ..
}

And then we’ll do:

window.onload = bodyOnLoad;

However, we also want to make sure our setting of the load event doesn’t remove some other setting. This is done by also keeping any older events.

We store the previous on load event by doing;

var prevOnLoad = window.onload;

And we redefine our bodyOnLoad function:

function bodyOnLoad() {
  prevOnLoad();
  ..
  ..
}

However, we can make the creation of the function and the setting of the event a little bit more effective by doing:

window.onload = function() {
  prevOnLoad();

  ..
  ..
}

You still need to get prevOnLoad before you do that

This becomes even more obvious once we create a function for adding new load events:

function addLoadEvent(func) {
  var prevOnLoad = window.onload;
  window.onload = function() {
    prevOnLoad();
    func();
  }
}

In this way, we can concentrate on creating the new load event outside of the function for adding it to the window.onload.

function myEvent(){
  ..
  ..
}
addLoadEvent(myEvent);

We might even do:

addLoadEvent(
  function (){
    ..
    ..
  }
);

Notice the difference between curly braces “{}” and parenthesis “()”

Finally, we have to make sure there is a load event set for the window before calling it from the new event, so we need to check for this:

function addLoadEvent(func) {
  var prevOnLoad = window.onload;
  if (typeof prevOnLoad != 'function') {
    window.onload = func;
  }
  else {
    window.onload = function() {
      prevOnLoad();
      func();
    }
  }
}
Computers, Humor

Programming humor

In case you wondered. Sure, programming can be humorous, but this is more about looking at programming with humor. Or, well, I’ve found a few funny things I’d like to share… XML is like violence: if it doesn’t solve your problem, you’re not using enough of it.

People who make buttumptions about their censoring settings, will be embarbutted when they repeat this clbuttic mistake.

Computers

Programming booleans

When looking at other programmer’s code I’m sometimes surprised with things like this:

exportDocumentView(java.lang.String absPath, java.io.OutputStream out,
boolean skipBinary, boolean noRecurse)

And in such prominent frameworks as Java Content Repository as well.

What’s my problem then? Double negations. In order to do exportDocumentView and get binary data and recursive export you’ll need to do:

exportDocumentView(“/path/to/my/Node/”, System.out, false, false)

Sure I can handle it… but… false to opt something in? I find it rather fishy. Call me an idiot but my brain just don’t deal with that kind of stuff easily…

What I would have wanted instead was:

exportDocumentView(java.lang.String absPath, java.io.OutputStream out,
boolean includeBinary, boolean recursive)

Which would have been called like:

exportDocumentView(“/path/to/my/Node/”, System.out, true, true)

For when we want binary data and recursive export, and like this for the case when we don’t want either or both:

exportDocumentView(“/path/to/my/Node/”, System.out, false, true)
exportDocumentView(“/path/to/my/Node/”, System.out, true, false)
exportDocumentView(“/path/to/my/Node/”, System.out, false, false)

I’m just saying. In my world false means “no” and “no” means don’t give me something or don’t do something:

“Don’t return binary data.”
“Don’t recurse the tree of nodes.”

To be compared with:

“Don’t skip binary data.”
“Don’t do no recursing.”

(But you’re free to curse? :o)

Computers

Using UUIDs to Prevent Broken Links

I don’t know if someone has proposed this before, but how about using UUIDs to prevent broken links?

A UUID, Universally Unique Identifier, is a hexadecimal number divided into five sections. A UUID has the special quality that it is universally unique. This means two people on each side of the world could create a UUID each at the exact same time, and still be sure their UUIDs are not identical. In fact they can create a large number of UUIDs and still be sure they are not identical. (The same goes for two people on the same server.)

This quality makes UUIDs a perfect tool for assigning unique IDs to web pages or other Internet resources (in fact any resource of any kind, your dog, the cuttlery in your drawers, you name it.)

This could be done like this:

Step 1: Place the UUID on the page

First a UUID has to be put on the webpage, perhaps with a meta-tag, or with plain text on the page.

With a meta tag it could be done like:

<meta name=”UUID” content=”8523813a-7c47-4cd9-ad78-09c14dfb505f”/>

Or on the page, like:

UUID: 8523813a-7c47-4cd9-ad78-09c14dfb505f

Step 2: Find the UUID

The second step would be to make sure every time a program stores a URL to the page it also stores the UUID. (When creating bookmarks, or linking from one site to another etc).

So, once the page get lost, either because the link has changed, the page has been moved or something similar, the browser (or site) can use the UUID to find the page again.

The second step obviously demands a search engine (or some other central registry) that utilizes UUIDs in it’s index since the system does require some kind of central processing for keeping track of a UUID-to-page-link.

A UUID is not a particularly good URI since even UUIDs generated at the same host just a few seconds apart are still totally different from each others (this actually depends on implementation, but one should not assume UUIDs from the same host shares any similarities).

This however is also one of the strengths of UUIDs since it means an Internet resource should be possible to locate regardless of its physical location (in a contrary to ordinary http-URLs that are tightly bound to their location — they start with the server name).

Since a UUID (per definition) is universally unique, it is fairly simple to generate one wherever you are, and use it in a page, be sure there are no duplicates and locate the exact page of the UUID again.

A Google experiment

I’ve placed the text “UUID: 8523813a-7c47-4cd9-ad78-09c14dfb505f” on this page. (Several times now). As far as I’ve been able to discern, Google indexes even such arbitrary information as UUID data (the exact string “8523813a-7c47-4cd9-ad78-09c14dfb505f” to be precise, check out this page with a discussion on how to use UUIDs to make pages unique… It has nothing to do with this discussion but is an interesting example on how UUIDs could be used with Google).

By searching for “8523813a-7c47-4cd9-ad78-09c14dfb505f” it should be possible to locate this page… (see if it works? — Give Google time to index the page though… Update: the above link seems to not work, but this one [searching for the UUID with “-” replaced to space — or “+”], however, does…)

Finally

The page localization should work regardless of the page’s position, site, or anything. In fact, as long as the UUID is still there, it should even be possible to place this text in a document of type Word/OpenDocument/PDF or any other format a search engine can index, and the text would still be possible to find with nothing but the UUID.

Obviously the end result of this technology would be that there is no “search-engine-in-between” but instead whenever the link is lost, the caller goes to the central repository/search engine (or some other place) and locate the page, then links to it automatically. It should even be smart enough to retry until it finds a link that works if a UUID has several possible links.