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  • Recommendations for an in memory database vs thread safe data structures

    - by yx
    TLDR: What are the pros/cons of using an in-memory database vs locks and concurrent data structures? I am currently working on an application that has many (possibly remote) displays that collect live data from multiple data sources and renders them on screen in real time. One of the other developers have suggested the use of an in memory database instead of doing it the standard way our other systems behaves, which is to use concurrent hashmaps, queues, arrays, and other objects to store the graphical objects and handling them safely with locks if necessary. His argument is that the DB will lessen the need to worry about concurrency since it will handle read/write locks automatically, and also the DB will offer an easier way to structure the data into as many tables as we need instead of having create hashmaps of hashmaps of lists, etc and keeping track of it all. I do not have much DB experience myself so I am asking fellow SO users what experiences they have had and what are the pros & cons of inserting the DB into the system?

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  • Returning a variable in a public void...

    - by James Rattray
    Hello, I'm abit new to programming Android App's, however I have come across a problem, I can't find a way to make global variables -unlike other coding like php or VB.NET, are global variables possible? If not can someone find a way (and if possible implement the way into the code I will provide below) to get a value from the variable 'songtoplay' so I can use in another Public Void... Here is the code: final Spinner hubSpinner = (Spinner) findViewById(R.id.myspinner); ArrayAdapter adapter = ArrayAdapter.createFromResource( this, R.array.colours, android.R.layout.simple_spinner_item); adapter .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); hubSpinner.setAdapter(adapter); // hubSpinner.setOnItemSelectedListener(new OnItemSelectedListener() { public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) { //code Object ttestt = hubSpinner.getSelectedItem(); final String test2 = ttestt.toString(); Toast message1 = Toast.makeText(Textbox.this, test2, Toast.LENGTH_LONG); message1.show(); String songtoplay = test2; // Need songtoplay to be available in another 'Public Void' } public void onNothingSelected(AdapterView<?> parentView) { //Code } }); Basically, it gets the value from the Spinner 'hubSpinner' and displays it in a Toast. I then want it to return a value for string variable 'songtoplay' -or find a way to make it global or useable in another Public Void, (Which is will a button, -loading the song to be played) Please help me, Thanks alot. James

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  • Webapp: safetly update a shared List/Map in the AppContext

    - by al nik
    I've Lists and Maps in my WebAppContext. Most of the time these are only read by multiple Threads but sometimes there's the need to update or add some data. I'm wondering what's the best way to do this without incurring in a ConcurrentModificationException. I think that using CopyOnWriteArrayList I can achieve what I want in terms of - I do not have to sync on every read operation- I can safety update the list while other threads are reading it. Is this the best solution? What about Maps?

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  • OO vs Simplicity when it comes to user interaction

    - by Oetzi
    Firstly, sorry if this question is rather vague but it's something I'd really like an answer to. As a project over summer while I have some downtime from Uni I am going to build a monopoly game. This question is more about the general idea of the problem however, rather than the specific task I'm trying to carry out. I decided to build this with a bottom up approach, creating just movement around a forty space board and then moving on to interaction with spaces. I realised that I was quite unsure of the best way of proceeding with this and I am torn between two design ideas: Giving every space its own object, all sub-classes of a Space object so the interaction can be defined by the space object itself. I could do this by implementing different land() methods for each type of space. Only giving the Properties and Utilities (as each property has unique features) objects and creating methods for dealing with the buying/renting etc in the main class of the program (or Board as I'm calling it). Spaces like go and super tax could be implemented by a small set of conditionals checking to see if player is on a special space. Option 1 is obviously the OO (and I feel the correct) way of doing things but I'd like to only have to handle user interaction from the programs main class. In other words, I don't want the space objects to be interacting with the player. Why? Errr. A lot of the coding I've done thus far has had this simplicity but I'm not sure if this is a pipe dream or not for larger projects. Should I really be handling user interaction in an entirely separate class? As you can see I am quite confused about this situation. Is there some way round this? And, does anyone have any advice on practical OO design that could help in general?

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  • Autocomplete server-side implementation

    - by toluju
    What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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  • Find messages[from-to]

    - by Alfred
    I would like to return all messages from certain key to a certain key. The class should be thread-safe and old keys should be able to be deleted say for example after 30 seconds. I was thinking of using a concurrentskiplistset or concurrentskiplist map. Also I was thinking of deleting the items from inside a newSingleThreadScheduledExecutor. I would like to know how you would implement this or maybe use a library?

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  • How Can i click on this element using XPATH in Web driver?

    - by Mike
    Here is the html..... <li> <input type="checkbox" checked="" name="selectedMstrPrivGroupList[9].mstrAuthorities[0].status"/> Add Dexter </li> How will I be able to click on this element. It is a check box. And I want to use XPath as I have close to 30+ checkboxes in the page, so that I can create a generic method and pass only the Webelement.. I tried the following but didn't work. Driver.findElement(By.xpath("//input[contains(.,'Add Dexter')]")).click(); Please help!! Thanks, Mike

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  • How to maintain base files for development environment central while allowing people to change their

    - by Ittai
    Hi, what I'd like to do is have files in a central location so that when I add people to my development team they can see the base version of these files but meanwhile have the ability for the rest of the team to work with their own local version. I know I can just put the files in source-control (we use Tortoiese-SVN) and have my team change the local versions but I'd rather not as the exclamation mark signaling the file has been changed and needs to be committed, quite frankly, irritates me greatly. I'll give two examples of what I mean: We use quite a few build.xml files which relate to a single properties files which contains many definitions. Some of them can be different between team-members (mainly temporary working directories) and I'd like a new team-member to have the ability to get the properties file with the base config but change it if they wish. Have the eclipse settings file in the SVN so that when a new team-member joins they can just retrieve the files from the server and have a base system running. If they wish they will be able to change some of these settings. Thanks, Ittai

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  • Updating position of JSlider Swing

    - by GLRockwell
    My apologies for posting tons of questions as of late. I'm trying to get a JSlider to update its position based on a constantly updating variable. The setValue(n) method doesn't seem to work. Is there any alternative? We're using this as a time marker for a music player.

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  • Autocompletion in Eclipse for Roo project

    - by niklassaers
    Hi guys, I've got a Roo project where I've made a couple of entities, and when I load up the project in Eclipse it loads up fine, but if I i.e. make an instance MyEntity entity and then write entity. I don't get any of my properties (i.e. getMyField) in the autocompletion list. If I write entity.getMyField() it compiles fine, that is taken care of by the aspects. How do I enable autocompletion for functions generated by the aspects? Cheers Nik

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  • How to handle major framework/dependency upgrades?

    - by APSampson
    Looking for some best practices on handling a major dependency upgrades within a project, assuming the use of a dependency management tool(e.g., Maven 2). Specifically, I'm interested in: How get an inherited application up-to-date(e.g., Spring 1.2.x to 2.5.x) What practices can be put into place to after such an overhaul to keep applications somewhat up-to-date Your own experiences or any articles/papers you've come across/found to be useful are welcome.

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  • Object can not be resolved.

    - by Gabriel A. Zorrilla
    I have this code: public class Window extends JFrame { public Window(){ ... JButton button = new JButton("OK"); getContentPane().add(button); ButtonHandler handler = new ButtonHandler(); button.addActionListener(handler); ... } private class ButtonHandler implements ActionListener { public void actionPerformed(ActionEvent event){ if (event.getSource() == button){ // <--- "button can not be resolved" System.out.println("Hello"); } } } I'm getting that error in Eclipse. I just made a (simplified) example found in a book, dont know what can be wrong. Knowledge eye required! :)

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  • How to increase the performance of a loop which runs for every 'n' minutes.

    - by GustlyWind
    Hi Giving small background to my requirement and what i had accomplished so far: There are 18 Scheduler tasks run at regular intervals (least being 30 mins) takes input of nearly 5000 eligible employees run into a static method for iteration and generates a mail content for that employee and mails. An average task takes about 9 min multiplied by 18 will be roughly 162 mins meanwhile there would be next tasks which will be in queue (I assume). So my plan is something like the below loop try { // Handle Arraylist of alerts eligible employees Iterator employee = empIDs.iterator(); while (employee.hasNext()) { ScheduledImplementation.getInstance().sendAlertInfoToEmpForGivenAlertType((Long)employee.next(), configType,schedType); } } catch (Exception vEx) { _log.error("Exception Caught During sending " + configType + " messages:" + configType, vEx); } Since I know how many employees would come to my method I will divide the while loop into two and perform simultaneous operations on two or three employees at a time. Is this possible. Or is there any other ways I can improve the performance. Some of the things I had implemented so far 1.Wherever possible made methods static and variables too Didn't bother to catch exceptions and send back because these are background tasks. (And I assume this improves performance) Get the DB values in one query instead of multiple hits. If am successful in optimizing the while loop I think i can save couple of mins. Thanks

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  • SQl function in android

    - by rui.pereira
    Cursor cursor = db.rawQuery("SELECT COUNT(rat) FROM "+ TABLE_NAME_EXTRA +" apkid=\""+apkid, null); cursor.moveToFirst(); int somatotal = cursor.getInt(0); I'm trying to do a SQL function like count and sum, but this code returns a exception saying "emptyvalues". anyone know why?

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  • How do these user/userParam references relate to the Customer and Account lookups?

    - by plath
    In the following code example how do the user/userParam references relate to the Customer and Account lookups and what is the relationship between Customer and Account? // PersistenceManager pm = ...; Transaction tx = pm.currentTransaction(); User user = userService.currentUser(); List<Account> accounts = new ArrayList<Account>(); try { tx.begin(); Query query = pm.newQuery("select from Customer " + "where user == userParam " + "parameters User userParam"); List<Customer> customers = (List<Customer>) query.execute(user); query = pm.newQuery("select from Account " + "where parent-pk == keyParam " + "parameters Key keyParam"); for (Customer customer : customers) { accounts.addAll((List<Account>) query.execute(customer.key)); } } finally { if (tx.isActive()) { tx.rollback(); } }

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  • How do these user/userParam references relate to the Customer and Account lookups?

    - by marmalade
    In the following code example how do the user/userParam references relate to the Customer and Account lookups and what is the relationship between Customer and Account? // PersistenceManager pm = ...; Transaction tx = pm.currentTransaction(); User user = userService.currentUser(); List<Account> accounts = new ArrayList<Account>(); try { tx.begin(); Query query = pm.newQuery("select from Customer " + "where user == userParam " + "parameters User userParam"); List<Customer> customers = (List<Customer>) query.execute(user); query = pm.newQuery("select from Account " + "where parent-pk == keyParam " + "parameters Key keyParam"); for (Customer customer : customers) { accounts.addAll((List<Account>) query.execute(customer.key)); } } finally { if (tx.isActive()) { tx.rollback(); } }

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  • Updatable false behvior incosistent

    - by jpanewbie
    I need LastUpdatedDttm to be updated by SYSDATE whenever record is updated. But below annoataions do nt work as desired. SYSDATE is inserted only once and not updated for subsequent updations. Also, lastUpdDTTM is not part of sql generated by hibernate. @Generated(GenerationTime.ALWAYS) @Column(name="LAST_UPDATED_DTTM",insertable=false,updatable=true, columnDefinition ="timestamp default SYSDATE") private Date lastUpdDTTM; @Generated(GenerationTime.ALWAYS) @Column(name="CREATED_DTTM", insertable=false, updatable=false) private Date createdDTTM;

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  • smartGWT: retrieve data from server to populate a listGrid

    - by Gabriele
    I'm searching a way to populate a ListGrid with an XML response from a server. This is an example of my server response: <?xml version="1.0" encoding="UTF-8"?> <tbody id="tbody"> <tr> <word>The</word> <frequence>12</frequence> </tr> <tr> <word>best</word> <frequence>3</frequence> </tr> ... And this is how I can populate the ListGrid using a file (item.xml) where I have saved the xml result: public class Frequenze extends DataSource { private static Frequenze instance = null; public static Frequenze getInstance() { if (instance == null) { instance = new Frequenze("frequence"); } return instance; } public Frequenze(String id) { setID(id); setRecordXPath("//tr"); DataSourceTextField wordField = new DataSourceTextField("word", "Word"); wordField.setRequired(true); DataSourceIntegerField frequenceField = new DataSourceIntegerField("frequence", "Frequence"); frequenceField.setRequired(true); setFields(wordField, frequenceField); setDataURL("ds/item.xml"); setClientOnly(true); } } Now I want not to use the file, but I'm searching a way to retrieve the data directly from the server. Anyone know how I get this?

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  • Glassfish log files analysis

    - by Cem
    Can I get some recommendations for good log analysis software for Glassfish log files? Since it will not vary from application server to application server dramatically, I guess that there is a common solution for all servers. Thanks

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