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On February 19 2015 01:46 Nesserev wrote:I almost never use std::list. Stroustrup pointed out in one of his presentations that you should almost always prefer std::vector over std::list in practice, even though, theoretically, there are a lot of uses for lists. The biggest disadvantage of std::vector is of course that insertion/deletion somewhere in the vector, requires the repositioning of all elements behind the inserted/deleted element(s). Note that insertion/deletion at the back of the vector is amortized constant time. On the other hand, insertion/deletion is constant time anywhere in linked lists. The biggest disadvantage of linked lists is that it's rather bad at some very convenient stuff, like size(), or access through an index (which is why these are not provided by the stl). Now here's the big hidden factor for why you shouldn't use lists: iteration. It's the only way to access the elements in a linked list, and it's also possible to do in a vector. If you iterate over all the elements of a vector, the iterator will just jump one object space further in memory to access the next element, which is very efficient. If you iterate over all the elements of a linked list, the iterator has to jump through memory to wherever the next element is. This form of access is very expensive, especially if you have list of millions of elements. If one were to compare the frequency and cost of moving elements in a vector, to that of iterating the elements of a list, the conclusion would be that the list will always perform worse than the vector. Of course, the way I presented it probably leaves room for some fallacies and discussion, but trust me on this one. From the point of view of a programming language, I very much do like the std::list class. Its interface is just so elegant. std::forward_list is an abomination though... first person I see using that class, gets a dropkick in the face.
Why? Isn't that class supposed to be an optimised version of List if you only need forward iteration? I can't think of a possible use case but I'm sure it fits some purpose.
Edit: There you go: http://stackoverflow.com/a/11563749
As I previously said, it's probably for optimisation purposes. E.g. on embedded systems?
Isn't the difference too high though? I thought pointers are relatively cheap in terms of memory, and doesn't doubly link list just have one extra pointer which points to the previous node?
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hey guys, quick question
i need to do a project to make a java web application (mvc website with its own users database) that allows a user to search a 3rd party website database using its API like http://www.animenewsnetwork.com/encyclopedia/api.php or like the IMDB database API.
e.g. user searches for movie , my website sends the request to IMDB or ANN website , retrieves XML and displays a response to my user
would it be possible for someone to point me in the right direction with maybe a tutorial (youtube or google or otherwise) or keywords so i can search for how to do this in java EE? any keyword or hint would be wonderful
thanks guys
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On February 20 2015 03:43 darkness wrote:Show nested quote +On February 19 2015 01:46 Nesserev wrote:On February 18 2015 22:14 nunez wrote:i must profess my love for std::list: a beautiful contraption. I almost never use std::list. Stroustrup pointed out in one of his presentations that you should almost always prefer std::vector over std::list in practice, even though, theoretically, there are a lot of uses for lists. The biggest disadvantage of std::vector is of course that insertion/deletion somewhere in the vector, requires the repositioning of all elements behind the inserted/deleted element(s). Note that insertion/deletion at the back of the vector is amortized constant time. On the other hand, insertion/deletion is constant time anywhere in linked lists. The biggest disadvantage of linked lists is that it's rather bad at some very convenient stuff, like size(), or access through an index (which is why these are not provided by the stl). Now here's the big hidden factor for why you shouldn't use lists: iteration. It's the only way to access the elements in a linked list, and it's also possible to do in a vector. If you iterate over all the elements of a vector, the iterator will just jump one object space further in memory to access the next element, which is very efficient. If you iterate over all the elements of a linked list, the iterator has to jump through memory to wherever the next element is. This form of access is very expensive, especially if you have list of millions of elements. If one were to compare the frequency and cost of moving elements in a vector, to that of iterating the elements of a list, the conclusion would be that the list will always perform worse than the vector. Of course, the way I presented it probably leaves room for some fallacies and discussion, but trust me on this one. From the point of view of a programming language, I very much do like the std::list class. Its interface is just so elegant. std::forward_list is an abomination though... first person I see using that class, gets a dropkick in the face. Why? Isn't that class supposed to be an optimised version of List if you only need forward iteration? I can't think of a possible use case but I'm sure it fits some purpose. Edit: There you go: http://stackoverflow.com/a/11563749As I previously said, it's probably for optimisation purposes. E.g. on embedded systems? Isn't the difference too high though? I thought pointers are relatively cheap in terms of memory, and doesn't doubly link list just have one extra pointer which points to the previous node?
-misread-
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On February 20 2015 03:43 darkness wrote:
As I previously said, it's probably for optimisation purposes. E.g. on embedded systems?
If you're doing safety critical embedded development, dynamic allocation is a big no-no, so lists and vectors are not very useful in this regard.
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the stl containers are templated on allocator.
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On February 20 2015 07:24 bangsholt wrote:Show nested quote +On February 20 2015 03:43 darkness wrote:
As I previously said, it's probably for optimisation purposes. E.g. on embedded systems? If you're doing safety critical embedded development, dynamic allocation is a big no-no, so lists and vectors are not very useful in this regard.
Not exactly true as a ton of embedded applications use heap and dynamic page mapping to use large swaths of memory temporarily without crippling the system. Many embedded OS have filesystems and networking stacks which both benefit greatly from dynamic allocation.
The worst case, when every greedy module in the system needs its maximum memory at the same time, should not halt your critical programs, and when such a day comes, low priority modules should fail gracefully when you get an allocation failure. Of course, it's simpler to just not malloc or grab any dynamic memory.
It is pretty rare to see an embedded C++ program use STL, even now with 2.4GHz 48 core embedded systems with 4GB of RAM, but it does happen. I recall a recent military aviation project I worked on does, but thats not surprising given the defense industry's usual program bloat.+ Show Spoiler + I just realized some of these embedded projects are more powerful than my gaming rig
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On February 20 2015 03:48 FFGenerations wrote:hey guys, quick question i need to do a project to make a java web application (mvc website with its own users database) that allows a user to search a 3rd party website database using its API like http://www.animenewsnetwork.com/encyclopedia/api.php or like the IMDB database API. e.g. user searches for movie , my website sends the request to IMDB or ANN website , retrieves XML and displays a response to my user would it be possible for someone to point me in the right direction with maybe a tutorial (youtube or google or otherwise) or keywords so i can search for how to do this in java EE? any keyword or hint would be wonderful thanks guys
You may want to read up on web services. Decide if you want to use REST or SOAP and go for it 
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On February 20 2015 10:23 Manit0u wrote:Show nested quote +On February 20 2015 03:48 FFGenerations wrote:hey guys, quick question i need to do a project to make a java web application (mvc website with its own users database) that allows a user to search a 3rd party website database using its API like http://www.animenewsnetwork.com/encyclopedia/api.php or like the IMDB database API. e.g. user searches for movie , my website sends the request to IMDB or ANN website , retrieves XML and displays a response to my user would it be possible for someone to point me in the right direction with maybe a tutorial (youtube or google or otherwise) or keywords so i can search for how to do this in java EE? any keyword or hint would be wonderful thanks guys You may want to read up on web services. Decide if you want to use REST or SOAP and go for it
tnx i remembered that just now lol. im so shit. my grades are all fail so far but i heard they discount your worst grade in my special case so i dodged a bullet there. only 2 months then i can look for a job...dont care what job just want a job XD
errr that was a pm but whatever lol
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On February 20 2015 10:23 Manit0u wrote:Show nested quote +On February 20 2015 03:48 FFGenerations wrote:hey guys, quick question i need to do a project to make a java web application (mvc website with its own users database) that allows a user to search a 3rd party website database using its API like http://www.animenewsnetwork.com/encyclopedia/api.php or like the IMDB database API. e.g. user searches for movie , my website sends the request to IMDB or ANN website , retrieves XML and displays a response to my user would it be possible for someone to point me in the right direction with maybe a tutorial (youtube or google or otherwise) or keywords so i can search for how to do this in java EE? any keyword or hint would be wonderful thanks guys You may want to read up on web services. Decide if you want to use REST or SOAP and go for it
I think he's consuming the services, not implementing them.
Does it have to be part of the full EE stack or just a java webapp? Which container are you running in?
Guess I'll just elaborate without answers.. if it has to be EE and you are using glassfish there isn't really a whole lot of flexibility or even reason to look at options. Start looking at JSF tutorials.
If not, and you are just running in tomcat, you can try spring mvc which might more quickly help you get going with users. If it just has to be java-ish, groovy on grails could get you going.
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On February 20 2015 11:34 berated- wrote:Show nested quote +On February 20 2015 10:23 Manit0u wrote:On February 20 2015 03:48 FFGenerations wrote:hey guys, quick question i need to do a project to make a java web application (mvc website with its own users database) that allows a user to search a 3rd party website database using its API like http://www.animenewsnetwork.com/encyclopedia/api.php or like the IMDB database API. e.g. user searches for movie , my website sends the request to IMDB or ANN website , retrieves XML and displays a response to my user would it be possible for someone to point me in the right direction with maybe a tutorial (youtube or google or otherwise) or keywords so i can search for how to do this in java EE? any keyword or hint would be wonderful thanks guys You may want to read up on web services. Decide if you want to use REST or SOAP and go for it I think he's consuming the services, not implementing them. Does it have to be part of the full EE stack or just a java webapp? Which container are you running in? Guess I'll just elaborate without answers.. if it has to be EE and you are using glassfish there isn't really a whole lot of flexibility or even reason to look at options. Start looking at JSF tutorials. If not, and you are just running in tomcat, you can try spring mvc which might more quickly help you get going with users. If it just has to be java-ish, groovy on grails could get you going.
thanks dude. im using java EE with glassfish and have gone through the netbeans tutorial https://netbeans.org/kb/docs/javaee/ecommerce/intro.html which seems to just go on FOREVER with so many minute details, its insane .
thats as far as i got so far. my personal tutor (doesnt take me for any classes, nor do i have any web or java classes) is into the core java EE with netbeans and no frameworks and so im just gonna use that......
i am consuming the services. so it should be pretty simple thing, i just need example or tutorial or something to go through. then i can start to design the whole thing somehow XD
ill search "jsf rest tutorial" and go from there i guess (tho i welcome further comments :D ) tnx all
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On February 20 2015 11:34 berated- wrote:Show nested quote +On February 20 2015 10:23 Manit0u wrote:On February 20 2015 03:48 FFGenerations wrote:hey guys, quick question i need to do a project to make a java web application (mvc website with its own users database) that allows a user to search a 3rd party website database using its API like http://www.animenewsnetwork.com/encyclopedia/api.php or like the IMDB database API. e.g. user searches for movie , my website sends the request to IMDB or ANN website , retrieves XML and displays a response to my user would it be possible for someone to point me in the right direction with maybe a tutorial (youtube or google or otherwise) or keywords so i can search for how to do this in java EE? any keyword or hint would be wonderful thanks guys You may want to read up on web services. Decide if you want to use REST or SOAP and go for it I think he's consuming the services, not implementing them. Does it have to be part of the full EE stack or just a java webapp? Which container are you running in? Guess I'll just elaborate without answers.. if it has to be EE and you are using glassfish there isn't really a whole lot of flexibility or even reason to look at options. Start looking at JSF tutorials. If not, and you are just running in tomcat, you can try spring mvc which might more quickly help you get going with users. If it just has to be java-ish, groovy on grails could get you going.
Well, even for consuming the services you might want to introduce a service that communicates with external service. Then you have it all nice and well. Some REST api serving the content from external api directly to your users via ajax calls and what not.
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does this logic make sense or am i overcomplicating it? is this too many database actions or is this normal?
use case: on my website, user wants to create a list of his favourite movies
1) User searches for a movie
2) System requests search result of movie names + thumbnail picture URLs from external website (consuming 3rd party REST API)
3) System displays search results to user (movie name + thumbnail image)
4) User clicks on a search result
5) System adds the clicked movie's name + thumbnail URL to a temporary storage list (session state?????)
6) User makes more searches and clicks on more results
7) User clicks Finish
8) System updates my database with movieID movie names + thumbnail URLs
9) System updates my database with a movie list ListID that contains the selected movieID movies
10) System generates an image consisting of ListID's movieID thumbnails (so we have 1 composite picture showing all movies in 1 jpg picture)
11) System updates my database ListID to insert the URL of the generated image
12) System updates my database, adding ListID to user's UserID
( 13) System takes user to UserID's ListID page )
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8 and 9 are a bit questionable. Why are you storing the Movie names and their Thumbnails in your own database when every user accesses them from the 3rd party every time? Seems like you're storing information and files that won't be accessed again.
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so....the movie data will be needed:
1) when a user performs a search
2) when a user pulls up one of his saved movie lists (to view or edit it)
so when we save the user's movie list we might aswell save the thumbnail url of the movies along with their names
theoretically if we're saving these to our own database we could check this database before performing any search request to the 3rd party API .........
i wonder what performance impact that would have, if we're trying to access our own database and then the 3rd party one if nothing is found? the other issue with this is that it would remove freshness of directly accessing the 3rd party database.....
does that make sense? (the fact that we're storing the user's movie lists for future use)
lets change 13 to say...
13) System takes user to user's ListID page which displays his list of movies alongside their thumbnail images and offers the hyperlink to his generated composite jpeg, a link to edit the list and a link to delete the list. (users can have multiple saved lists)
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Sounds like all you need to store is the list of movie ids and your generated image. Then you grab the list from your DB and send a request to the 3rd party based off of that.
Storing movie urls and thumbnails in your DB is definitely not necessary. Testing your DB before the 3rd party one kind of defeats the purpose and adds unnecessary problems:
1. More DB queries = not good.
2. More stuff in the DB = not good.
3. Possibility of outdated data = not good (although it might be counter-balanced by it working even if 3rd party api/site is down, but that's an edge case).
Updated flowchart:
1) User searches for a movie
2) System requests search result of movie names + thumbnail picture URLs from external website (consuming 3rd party REST API)
3) System displays search results to user (movie name + thumbnail image)
4) User clicks on a search result
5) System adds the clicked movie's name + thumbnail URL to a temporary storage list (session state?????)
6) User makes more searches and clicks on more results
7) User clicks Finish
8) System generates an image consisting of movie thumbnails (so we have 1 composite picture showing all movies in 1 jpg picture)
9) System updates my database with a movie list that contains the selected movies, composite image and user id
10) System takes user to user's movie list page
Notice only 1 DB query instead of 4 in the original idea and 3 less steps to take. It could even be optimized further.
All you need is a single table (movieList) with fields:
movies - storing the movie id's, how you do it is up to you, json, ; delimited string etc.
picture - for your composite picture resource (url)
user_id - to link the list with the user
You can update all the fields at once, with a single query. Don't forget to create the many-to-one relation on the lists-to-user tables.
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what happens when the user goes to view/edit his list? i want him to be able to search/edit the list and this would involve displaying to him the individual title's thumbnail images again (not the composite image)
1) user clicks edit list
2) system sends a request to the API to retrieve the thumbnail image urls of the titles
3) system displays the thumbnail images
do you see what i mean by needing the thumbnail images still? the composite image is just a one-off side-product
i just saw my tutor and he said i might want to store the actual thumbnail images myself and employ a caching technique to ensure freshness (like .... update them once a week or some other stuff)
(he also said you wont know unless you hurry up and implement something)
ill re-read your post in a bit
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that's stupid and you shouldn't listen to your teacher, you shouldn't be caching images if all you're doing is retrieving image urls. totally unnecessary. let the user's client cache the images (what are you building the frontend as anyways)
i feel like you're planning this way too much. this isn't a type of project that needs to be scoped out so definitively (unless the scoping is part of the project?). i'd be a lot more iterative and prototypy with this. you're going to have so many more requirements (frankly i'm not sure you've outlined all of your requirements for yourself well yet from what i'm reading) that it doesn't make sense to focus so hard on perfecting the system, when it's going to change subject to any other requirements you have.... don't think about caching and optimizing until you actually run into problems with it.
(sorry in advance if i sound angry/unreasonably mean btw, i think it's the lack of caps)
(also no clue if you're focusing hard on this or just asking a question that blew up cause everyone has a response)
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On February 20 2015 19:35 FFGenerations wrote:
what happens when the user goes to view/edit his list? i want him to be able to search/edit the list and this would involve displaying to him the individual title's thumbnail images again (not the composite image)
1) user clicks edit list
2) system sends a request to the API to retrieve the thumbnail image urls of the titles
3) system displays the thumbnail images
do you see what i mean by needing the thumbnail images still? the composite image is just a one-off side-product
i just saw my tutor and he said i might want to store the actual thumbnail images myself and employ a caching technique to ensure freshness (like .... update them once a week or some other stuff)
(he also said you wont know unless you hurry up and implement something)
ill re-read your post in a bit
You didn't get me. You store your composite image because that's something you can't get from the 3rd party and generating it every time is a waste of resources. You also only store movie ids as they figure in the 3rd party api so that when the user requests the list you make an external call of "gief names + thumbnails for movies: mov1, mov2, mov3...". No need to store them in your own DB. Also, thumbnails will link to the 3rd party servers, which have cached it already and so probably did your user's browser.
Don't add extra work for your system and yourself if it's not necessary.
Pretty much what Blisse said, but at the time of writing this his post was empty 
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that makes sense, thanks both
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EPT
