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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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• Are there any simple languages implemented using ANTLR or similar?

  - by etheros

  I'm trying to build a simple interpreted language for learning purposes. I've read countless theory and tutorials on ANTLR and JavaCC, but I can't figure out how to actually make it do something useful. I learn best by "taking something apart and putting it back together again", so, are there any working examples of simple languages implemented with the help of tools such as ANTLR, or similar? Something like the following might be nice: x = 1 if x == 1 print "true"

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• How could I get an .ear's filesize at runtime?

  - by adam

  I started out attempting to do this with the Length ant task, but realized that that would be done before the ear is packaged. Packaging the ear, then checking the file size, and then placing it in the ear would effect the size of the ear. Is there a way to get the ear's size programmatically at run-time? Or perhaps an MBean that would have that information?

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• List with checkbox using lwuit in j2me

  - by learn

  I am using LWUIT for getting a search facility for selection in the list. now i want to know how to display the list with checkbox? list=new List(vector); cform.addComponent(list); cform.addComponent(t); cform.show();

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• Fastest way to put contents of Set<String> to a single String with words separated by a whitespace?

  - by Lars Andren

  I have a few Set<String>s and want to transform each of these into a single String where each element of the original Set is separated by a whitespace " ". A naive first approach is doing it like this Set<String> set_1; Set<String> set_2; StringBuilder builder = new StringBuilder(); for (String str : set_1) { builder.append(str).append(" "); } this.string_1 = builder.toString(); builder = new StringBuilder(); for (String str : set_2) { builder.append(str).append(" "); } this.string_2 = builder.toString(); Can anyone think of a faster, prettier or more efficient way to do this?

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• Constructor versus setter injection

  - by Chris

  Hi, I'm currently designing an API where I wish to allow configuration via a variety of methods. One method is via an XML configuration schema and another method is through an API that I wish to play nicely with Spring. My XML schema parsing code was previously hidden and therefore the only concern was for it to work but now I wish to build a public API and I'm quite concerned about best-practice. It seems that many favor javabean type PoJo's with default zero parameter constructors and then setter injection. The problem I am trying to tackle is that some setter methods implementations are dependent on other setter methods being called before them in sequence. I could write anal setters that will tolerate themselves being called in many orders but that will not solve the problem of a user forgetting to set the appropriate setter and therefore the bean being in an incomplete state. The only solution I can think of is to forget about the objects being 'beans' and enforce the required parameters via constructor injection. An example of this is in the default setting of the id of a component based on the id of the parent components. My Interface public interface IMyIdentityInterface { public String getId(); /* A null value should create a unique meaningful default */ public void setId(String id); public IMyIdentityInterface getParent(); public void setParent(IMyIdentityInterface parent); } Base Implementation of interface: public abstract class MyIdentityBaseClass implements IMyIdentityInterface { private String _id; private IMyIdentityInterface _parent; public MyIdentityBaseClass () {} @Override public String getId() { return _id; } /** * If the id is null, then use the id of the parent component * appended with a lower-cased simple name of the current impl * class along with a counter suffix to enforce uniqueness */ @Override public void setId(String id) { if (id == null) { IMyIdentityInterface parent = getParent(); if (parent == null) { // this may be the top level component or it may be that // the user called setId() before setParent(..) } else { _id = Helpers.makeIdFromParent(parent,getClass()); } } else { _id = id; } } @Override public IMyIdentityInterface getParent() { return _parent; } @Override public void setParent(IMyIdentityInterface parent) { _parent = parent; } } Every component in the framework will have a parent except for the top level component. Using the setter type of injection, then the setters will have different behavior based on the order of the calling of the setters. In this case, would you agree, that a constructor taking a reference to the parent is better and dropping the parent setter method from the interface entirely? Is it considered bad practice if I wish to be able to configure these components using an IoC container? Chris

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• Creating lots of arrays

  - by Dmitry

  Hello, everybody! May be that is a stupid question. How to create, say, 30 arrays (it doesn't matter of what type, say, char[])? It seems to me that it is not a good idea, to create them one by one by hand. I want to do that using a "for" cycle, but how should I specify identifiers?

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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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• what are the types of interfaces? [closed]

  - by chandra

  Hi, I face this question in some interview. Can you tell me with examples? Thanks, chandu

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• Unable to set mouse cursor JLayeredPane

  - by Ones3k2

  I'm running into a problem that I can't seem to figure out nor find the answer anywhere on the web. I've got a JLayeredPane and when it only has one child Panel I am able to correctly set the cursor using setCursor(). The cursor shows up and everything is fine. But when I add an additional JPanel into the JLayeredPane the cursor no longer shows up for example this works: m_layeredPane = new JLayeredPane(); m_layeredPane.setLayout(new WBLayoutManager()); m_layeredPane.add(m_mediaPanel, new Integer(0)); // m_layeredPane.add(m_whiteboardPanel, new Integer(1)); m_layeredPane.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR)); // WORKS but this doesn't: m_layeredPane = new JLayeredPane(); m_layeredPane.setLayout(new WBLayoutManager()); m_layeredPane.add(m_mediaPanel, new Integer(0)); m_layeredPane.add(m_whiteboardPanel, new Integer(1)); m_layeredPane.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR)); // FAILS Anyone know how i can get custom cursors working within a JLayeredPane

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• storage service with google app engine.

  - by Bunny Rabbit

  i've been assigned a project to create a filestorage service on google applet engine.but i am really doubtful wheather it's possible or not given the 30 sec limit to process the response and moreover its the bigtable is just a database system not a storage server .am i correct ?

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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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• 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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• Counting viable sublist lengths from an array.

  - by Ben B.

  This is for a genetic algorithm fitness function, so it is important I can do this as efficiently as possible, as it will be repeated over and over. Lets say there is a function foo(int[] array) that returns true if the array is a "good" array and false if the array is a "bad" array. What makes it good or bad does not matter here. Given the full array [1,6,8,9,5,11,45,16,9], lets say that subarray [1,6,8] is a "good" array and [9,5,11,45] is a "good" array. Furthermore [5,11,45,16,9] is a "good" array, and also the longest "good" subarray. Notice that while [9,5,11,45] is a "good" array, and [5,11,45,16,9] is a "good" array, [9,5,11,45,16,9] is a "bad" array. We wants the length counts of all "good" arrays, but not subarrays of "good" arrays. Furthermore, as described above, a "good" array might begin in the middle of another "good" array, but the combination of the two might be a "bad" array.

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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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• How do I determine whether I am going "forward" or "backward" through my History in GWT?

  - by Stephen Cagle

  I am looking at History and History JavaDocs in GWT and I notice that there is no way to tell whether the forward or backward button was pressed (either pragmatically or by the user). The "button press" is handled by your registered addValueChangeHandler, but the only thing passed to the handler is a string on your history stack. There is no indication as to whether the "History" is moving "back" (using the back arrow button) or "forward" (using the right arrow button). Is there any way to determine this?

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• log4j: Log output of a specific class to a specific appender

  - by gubrutz

  I use log4j and would like to route the output of certain Loggers to specific files. I already have multiple appenders in place. Now, to make debugging easier, I want to tell log4j that the output generated by a specific class (e.g. foo.bar.Baz) should be written to a specific log file. Can this be done?

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• Customizing error handling of JAXB unmarshall process

  - by ekeren

  Assuming I have a schema that describes a root element class Root that contains a List<Entry> where the Entry class has a required field name. Here is how it looks in code: @XmlRootElement class Root{ @XmlElement(name="entry") public List<Entry> entries = Lists.newArrayList(); } @XmlRootElement class Entry{ @XmlElement(name="name",required=true) public String name; } If I supply the following XML for unmarshalling: <root> <entry> <name>ekeren</name> </entry> <entry> </entry> </root> I have a problem because the second entry does not contain a name. So unmarshall produces null. Is there a way to customize JAXB to unmarshall a Root object that will only contain the "good" entry?

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• Hook for redraw event in Blackberry

  - by Bendlas

  Is there a way to add a redraw callback to a live screen object, i.e. not via inheritance? Reasoning: I want to draw an overlay from an extension for widget sdk (substituting defunct position:absolute), so the screen is created by the bbwp stub. I can get it by Ui.getUiEngine().getActiveScreen() and draw on it quite nicely, but I need a way to redraw when appropriate. Note: I've abandoned the approach to push the overlay as a screen, because i couldn't make it transparent / find a way to pass events through.

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• Fast, lightweight XML parser

  - by joe90

  I have a specific format XML document that I will get pushed. This document will always be the same type so it's very strict. I need to parse this so that I can convert it into JSON (well, a slightly bastardized version so someone else can use it with DOJO). My question is, shall I use a very fast lightweight (no need for SAX, etc.) XML parser (any ideas?) or write my own, basically converting into a StringBuffer and spinning through the array? Basically, under the covers I assume all HTML parsers will spin thru the string (or memory buffer) and parse, producing output on the way through. Thanks //edit Thanks for the responses so far :) The xml will be between 3/4 lines to about 50 max (at the extreme)..

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• Hibernate: deletes not cascading for self-referencing entities

  - by jwaddell

  I have the following (simplified) Hibernate entities: @Entity @Table(name = "package") public abstract class Package { protected Content content; @ManyToOne(cascade = {javax.persistence.CascadeType.ALL}) @JoinColumn(name = "content_id") @Fetch(value = FetchMode.JOIN) public Content getContent() { return content; } public void setContent(Content content) { this.content = content; } } @Entity @Table(name = "content") public class Content { private Set<Content> subContents = new HashSet<Content>(); @ManyToMany(fetch = FetchType.EAGER) @JoinTable(name = "subcontents", joinColumns = {@JoinColumn(name = "content_id")}, inverseJoinColumns = {@JoinColumn(name = "elt")}) @Cascade(value = {org.hibernate.annotations.CascadeType.DELETE, org.hibernate.annotations.CascadeType.REPLICATE}) @Fetch(value = FetchMode.SUBSELECT) public Set<Content> getSubContents() { return subContents; } public void setSubContents(Set<Content> subContents) { this.subContents = subContents; } } So a Package has a Content, and a Content is self-referencing in that it has many sub-Contents (which may contain sub-Contents of their own etc). The relationships are required to be ManyToOne (Package to Content) and ManyToMany (Content to sub-Contents) but for the case I am currently testing each sub-Content only relates to one Package or Content. The problem is that when I delete a Package and flush the session, I get a Hibernate error stating that I'm violating a foreign key constraint on table subcontents, with a particular content_id still referenced from table subcontents. I've tried specifically (recursively) deleting the Contents before deleting the Package but I get the same error. Is there a reason why this entity tree is not being deleted properly?

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• How do I sort an ArrayList lexicographically?

  - by Jake

  I am trying to sort an ArrayList of Strings that represent card values. So, some cards contain letters ("King") and some contain Strings containing only a number ("7"). I know to use Collections.sort, but it only sorts Strings that contain letters. How do I get the ArrayList to be sorted by number as well as alphabetically?

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• Is there a decent HTML Junit report plugin for Maven?

  - by cats2ndlife

  I find the surefire-report plug-in very unsuitable to my working style. I clean the project all the time and I don't want to spend 5 min to rebuild the whole site every time I want to look at the test report in my browser. If I type mvn surefire-report:report-only, the generated report is too ugly and barely readable. What I'm looking for is something like ant's JUnitReport task. Is there one available out there already?

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• Setting Mnemonics and Hot Keys for a JOptionPane Dialog

  - by Daniel Bingham

  Is it possible to assign hotkeys and mnemonics to the buttons in a JOptionPane Dialog? I'd like to be able, in a JOptionPane generated message dialog with the options Yes, No and Cancel, press Y to hit the Yes button, N to hit the No button and escape to activate the escape button. Similarly in a dialog with Okay and Cancel buttons I'd like to be able to activate them with enter and escape. I've attempted passing JButtons into the JOptionPane's button Object array with the Mnemonics set already. The mnemonics work and the buttons show up correctly in the dialogs, however, they do not act properly when they are activated. Most noticeably they do not dispose of the dialog. What is the correct way to add hotkeys and Mnemonics to a JOptionPane Dialog's buttons? As always, my apologies ahead of time if this is a duplicate - I searched both Google and Stackoverflow and found nothing.

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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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