The Big Programming Thread - Page 467

On April 13 2014 05:23 Nesserev wrote:

Secondly, the Interface Segregation:
So, basically, what it comes down to, is that in the first example, every method that is used by the clients is part of one big Service class.

In the second example, every method that is used by a certain type of client, is put in a client specific class/interface. In the end, the Service class inherits all those specific classes/interfaces.

On April 13 2014 11:29 Nesserev wrote:

Well, that's what happens, the client derives its functionality from ITS contract with the server/service, BUT the service derives its interface from ALL of its contracts with clients.

I'll try to explain this in an abstract way via browsers (client) and servers(service), but I only have a basic understanding of how browsers work, so I hope I don't make (m)any mistakes:

Not all browsers support the same features, should this be a reason for all of them to use different services?
For example:
- All browsers are able to get pages, ofc.
- Browsers A and B both support text
- Browser A also supports images, while Browser B doesn't
- Browser A doesn't support videos, but Browser B does

So, the interfaces of browsers A and B should look like this:
Browser A: getPage, getText, getImage
Browser B: getPage, getText, getVideo

The interfaces serverside for every client individually would be (these are separate classes, will function as base classes)
Interface for A: sendPage, sendText, sendImage
Interface for B: sendPage, sendText, sendVideo

Now we unite those serverside interfaces into one service (Service class is derived from those base classes)
Service : sendPage, sendText, sendImage, sendVideo

I hope this helps a bit?

DISCLAIMER: I'm tired; it's 4:XX am in the morning; I don't want a technical discussion like the one 20-30 pages ago about multiple inheritance and the "dreaded" diamond of dead, because I used an example to explain the concept and nothing more.

On April 14 2014 03:45 Manit0u wrote:
Ok, I've run into some stupid C# problem. I'm a complete newbie with C# so please bear that in mind before laughing too hard:

public string Date {get; set;} // this is being set externally to either YYYY-MM-DD or "    "-"  "-"  " (whitespace in place of numbers)
private string[] dateCheck;

public void Configure() // being invoked externally, it sets the Date first then calls this method
{
    dateCheck = Date.Split('-'); // this gives me a null reference error so I can't proceed

    if (String.IsNullorWhitespace(dateCheck[0]))
    {
        Date = String.Empty;  // get rid of whitespace and hyphens if there's nothing to show
    }
}

I'm aware that my if check is probably complete garbage and will have to change it but I have no idea why does it throw an error when assigning the value to dateCheck (I have code that does exactly the same thing in another class and it works flawlessly).

Any help is appreciated.

if (Date != null) {
    dateCheck = Date.split('-');
    ...
} else {
    Console.WriteLine("Date not set.");
}

On April 14 2014 04:58 whiteLotus wrote:
just a dumb question, is it theoretically possible to actually learn programming through google, various online courses and tutorials, like lets say java,php,jq, maybe some python or C, and actually get a job as a web programmer or smth at some shitty ass company, or you would still ideally need some university courses like advanced math and shit? i dont mean anything like software developer at Blizzard or anything like that lol.

On April 14 2014 04:58 whiteLotus wrote:
just a dumb question, is it theoretically possible to actually learn programming through google, various online courses and tutorials, like lets say java,php,jq, maybe some python or C, and actually get a job as a web programmer or smth at some shitty ass company, or you would still ideally need some university courses like advanced math and shit? i dont mean anything like software developer at Blizzard or anything like that lol.

On April 14 2014 03:46 Ame wrote:
So I'm running Sieve of Eratosthenes and notice it takes a big hit to speed (on my laptop, was 'average' about 5 years ago) as the number to search to rises.

for (int i = 0; i < primeSieve.length; i++)
{
	if (!marked[i])
	{
		primeList.add(primeSieve[i]);
		//conditional print statement goes here sometimes
		if (primeSieve[i] < Math.sqrt(n))
		{
			for (int j = primeSieve[i]*primeSieve[i]; j <= n; j+=2*primeSieve[i])
			{
				marked[(j/2)-1] = true;
			}
		}	
	}
}

It's where the slowdown occurs that confuses me. With a cap of around n = 400m, it starts to really slow down around primeSieve[i] ~ 350m. At this point primeSieve[i] is way larger than sqrt(400m), so all that should be happening is check if marked[i] is true/false (boolean array) and then adding it to primeList (ArrayList<Integer>, size() at {primeSieve[i] = 350m} around 19m, init to be such that it never needs to be resized).

If I throw a 'print last prime' statement, it looks the program starts stuttering (prints out blocks of primes, freezes/waits about 5 seconds, prints out another block, etc) with the blocks printing out shrinking in size (towards the end before I stopped the program, it would only print out blocks of about 50 primes before freezing). Task Manager during runtime shows CPU usage ~99% and Physical Memory ~95% :|

It works fine up to n = 350m, ~doubling in run time between n = 150m (15 seconds) and n = 350m (30 seconds). But at 400m it goes LOLNO and runs for over 5-10 minutes before I cut it off. During the 400m run it still spits out primes through 350m fairly quickly (under a minute) before afking past 350m. JVM ran with heap size arguments to handle arrays and ArrayList.

Any idea what this might be or what I should be googling to find out more? Is this some crazy memory access thing?

On April 14 2014 04:29 Millitron wrote:
I'm not familiar with the Sieve of Eratosthenes, but is it possible that at around 350m primeSieve is over 2 billion? If primeSieve rolls over, you're screwed and stuck in the second for loop forever.

As for the weird printing, I think that's an artifact of system.out.print. Printing to the screen is horribly slow compared to doing math.

On April 14 2014 05:34 Cyx. wrote:
So wild guess - I might be really wrong - but on an old system with 2GB of RAM the max you'd be able to fit in RAM even with nothing else happening at all would be like 500 million ints or so, meaning that other things could reasonably eat up a couple hundred million of those spaces, leaving you with room for 300 million ints in memory before you started requiring a LOT of disk accesses, which would totally destroy your performance.

On April 14 2014 04:42 Manit0u wrote:
The thing is, the date was being set. I solved it by making the check in a different class though (before strings are joined with -).

On April 14 2014 05:23 spinesheath wrote:

You certainly can become good enough, the question is whether you can get an invitation to an interview. The majority of my knowledge is from the internet and books, university was a painful waste of time.
Proof techniques, combinatorics and matrices are pretty much the only things I learnt at univeristy and consider relevant. For comp sci stuff, it was far more efficient to just read it up myself.

But I don't know how good universities are where you live, and having a piece of paper saying "I provably spent some time on learning moderately relevant stuff" is rather effective for getting a job.

On April 14 2014 04:58 whiteLotus wrote:
just a dumb question, is it theoretically possible to actually learn programming through google, various online courses and tutorials, like lets say java,php,jq, maybe some python or C, and actually get a job as a web programmer or smth at some shitty ass company, or you would still ideally need some university courses like advanced math and shit? i dont mean anything like software developer at Blizzard or anything like that lol.

On April 14 2014 04:58 whiteLotus wrote:
just a dumb question, is it theoretically possible to actually learn programming through google, various online courses and tutorials, like lets say java,php,jq, maybe some python or C, and actually get a job as a web programmer or smth at some shitty ass company, or you would still ideally need some university courses like advanced math and shit? i dont mean anything like software developer at Blizzard or anything like that lol.

On April 14 2014 06:03 Ame wrote:


Whoops, some clarity: by 350m primeSieve, I meant the integer is ~350,000,000, so not worried about overflow yet, at least I don't think. And yea, I've run into the system.out.print being slow a bit back when I noticed run time went from minutes to seconds or something ridic by cutting out printing during steps the first time I tried to throw together a prime generator. :p

Still ran for over 5 minutes of nothing before I cut out without the print statements, so I don't think it was printing alone. I mainly threw in printing to make sure the ranges were still in values expected for the loop (checking for overflow) and to see where performance started taking a hit (the 350m figure).



I had a vague notion that it might have been a reason like this, but before now haven't read too much into RAM vs disk access/etc.. With your guess I will be doing so now.

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