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• When to trash hashmap contents to avoid performance degradation?

  - by Jack

  Hello, I'm woking on Java with a large (millions) hashmap that is actually built with a capacity of 10.000.000 and a load factor of .75 and it's used to cache some values since cached values become useless with time (not accessed anymore) but I can't remove useless ones while on the way I would like to entirely empty the cache when its performance starts to degrade. How can I decide when it's good to do it? For example, with 10 millions capacity and .75 should I empty it when it reaches 7.5 millions of elements? Because I tried various threshold values but I would like to have an analytic one. I've already tested the fact that emping it when it's quite full is a boost for perfomance (first 2-3 algorithm iterations after the wipe just fill it back, then it starts running faster than before the wipe) Thanks

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• How to flash the JFrame on Windows taskbar when it needs attention?

  - by japflap7stackoverflow

  Hi, i'm a computer science student working on a Yahoo Messenger - like program implemented in Java. My problem is that whenever the JTextArea inside my frame contains new message updates, the user must be prompted even when his/her frame is minimized. Is there a workaround on how to make the JFrame on the taskbar blink when updates are received? In short, i badly need a way to notify the user that the frame has been updated even though it is minimized. Is that possible? Thanks for you help. ^_^

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• Delegation, is this just opinionated or is there a common pattern?

  - by user1446714

  If I have a java class containing substantial code and I wish to add extra features, am I right in thinking the delegate class would have the additional features added as methods. Then my original class would create the delegate object and just call the extra functionality via the delegate instance? I am being told by somebody else that my original class should become the delegate and that the class containing the new functionality should contain an instance of the original class, to use as a delegate? This seemed a little backward to me, because there would be far more delegate calls because most of the code is now in the delegate.... I was always under the impression the delegate object would contain the additional new behaviour and an instance of it would be in the original class to inboke the new behaviour from?

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• Regular expression: who's greedier?

  - by polygenelubricants

  My primary concern is with the Java flavor, but I'd also appreciate information regarding others. Let's say you have a subpattern like this: (.*)(.*) Not very useful as is, but let's say these two capture groups (say, \1 and \2) are part of a bigger pattern that matches with backreferences to these groups, etc. So both are greedy, in that they try to capture as much as possible, only taking less when they have to. My question is: who's greedier? Does \1 get first priority, giving \2 its share only if it has to? What about: (.*)(.*)(.*) Let's assume that \1 does get first priority. Let's say it got too greedy, and then spit out a character. Who gets it first? Is it always \2 or can it be \3? Let's assume it's \2 that gets \1's rejection. If this still doesn't work, who spits out now? Does \2 spit to \3, or does \1 spit out another to \2 first?

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• Video encoding by servlet with MEncoder

  - by Andrey

  Hello. I was developing an application for video encoding on the server and got a problem with encoding video with MEncoder. This decoder doesn't work correctly when runned by a command line with Runtime.getRuntime().exec(“D:\mencoder\mnc\mencoder.exe video1.avi -o outvideo1.flv -of lavf -oac mp3lame -lameopts abr:br=64 -srate 22050 -ovc lavc -lavcopts vcodec=flv:vbitrate=300:mbd=2:mv0:trell:v4mv:cbp:last_pred=3 -vf scale=320:240,harddup -quiet”) ; The decoder launches and works in windows console with my parameters, but when it's run from a servlet it just hangs in process list and doesn't do anything before the web-server is stopped. When trying to use decoder from a simple java applcation, it runs correctly. Thanks for help.

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• EJB injection in Glassfish webapp

  - by g051051

  I've got an app that is trying to use @EJB annotation to inject remote references to EJBs in my ejb.jar file. I'm getting inconsistent results. In one case, I have a listener in web.xml that gets called and apparently has the EJB injected correctly, since I can see it connecting to the EJB and calling methods on it. In another class (a struts2 action) I get NPE when it tries to access the EJB reference. As far as I can tell, they're identical calls, in Java classes that live in the same .war file. As a work around, I added code in the constructor to lookup the EJBs by their global JNDI names, and it works fine. I just can't figure out why one @EJB works and not another.

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• Ideally How many connections I have to open ?

  - by ranjith-kumar-u

  Hi All, Recently I attended interview in java, the interviewer asked a question like below: I have a request which go throgh A,B,C modules and response go back throgh A , in module A I need to talk to database and again in module C I need to talk to database, so in this situation how many connections you will open and where do you close those connections? My Answer: I said that in module A I will open a connection and I will close it then and there, then control go to module B then module C, in module C again I will open one more connection and i will close it again. then he asked me again another question I want to open one connection per one request processing, how can i do this?

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• frame by frame animation not running

  - by abc

  well,i am a newbie to android..and i dont know whats wrong in my code.. this is my xml file <?xml version="1.0" encoding="utf-8"?> <animation-list xmlns:android="http://schemas.android.com/apk/res/android" id="selected" android:oneshot="false"> <item android:drawable="@drawable/w1" android:duration="50" /> <item android:drawable="@drawable/w2" android:duration="50" /> </animation-list> my java file ImageView img = (ImageView)findViewById(R.id.s); img.setBackgroundResource(R.anim.shape_animation); // Get the background, which has been compiled to an AnimationDrawable object. AnimationDrawable frameAnimation = (AnimationDrawable) img.getBackground(); // Start the animation (looped playback by default). frameAnimation.start();

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• Forward web request for directory index ('/') to an index.htm page in JBoss 4.0.5

  - by The Pretender

  I am using JBoss 4.0.5.GA to run a set of java applications. One of them is a web frontend, using Spring 1.4. URL mappings are configured in a way that 'fake' pages from request URLs are mapped to controllers. That means that when someone requests /index.htm, there's no actual 'index.htm' on disk, and that request maps to a specific conroller which then renders a jsp view. So the problem is as follows: I need to tell JBoss to somehow forward all requests for directory indices to corresponding 'index.htm' URLs like so: / ? /index.htm; /news/ ? /news/index.htm; /foo/bar/baz/ ? /foo/bar/baz/index.htm and so on. I can't use Tomcat's welcome-file-list feature because it looks for those files on disk, while all 'index.htm's are fake and don't actually exist on disk.

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• Add HttpOnly flag to cookies on the fly with Apache?

  - by Zack

  So I have a java webapp that uses tomcat with an apache proxy layer. I'm looking to make all cookies set from the app have the httpOnly flag. The problem with this is that tomcat is responsible for setting the flag from the application side and its default (in servlet api 2.5) is false. I was hoping I could set this flag for all cookies on the fly using apache. I've been trying different combinations and the closest I have gotten is setting the last cookie passed to httpOnly which is of course wrong: Header append Set-Cookie "; HttpOnly" I have no way of knowing what cookies/values are going to be passed from the app. Is this even possible?

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• Enums With Default Throw Clause?

  - by Tom Tresansky

  I noticed the following in the Java Language spec in the section on enumerations here: link switch(this) { case PLUS: return x + y; case MINUS: return x - y; case TIMES: return x * y; case DIVIDE: return x / y; } throw new AssertionError("Unknown op: " + this); However, looking at the switch statement definition section, I didn't notice this particular syntax (the associated throw statement) anywhere. Can I use this sort of "default case is throw an exception" syntactic sugar outside of enum definitions? Does it have any special name? Is this considered a good/bad practice for short-cutting this behavior of "anything not in the list throws an exception"?

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• What happens if a bean attempts to load the Spring application context in its constructor?

  - by Derek Mahar

  Given the following Spring application context and class A, what happens when you run class A? applicationContext.xml (in classpath): <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <bean name="a" class="A"/> </beans> A.java: class A { private ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml"); public static void main(String[] args) { A a = new A(); } }

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• Checking JRE version inside browser

  - by Brian Lewis

  Basically, I'm wanting to figure out the best way to check the user's JRE version on a web page. I have a link to a JNLP file that I only want to display if the user's JRE version is 1.6 or greater. I've been playing around with the deployJava JavaScript code (http://java.sun.com/javase/6/docs/technotes/guides/jweb/deployment_advice.html) and have gotten it to work in every browser but Safari (by using deployJava.versionCheck). For whatever reason, Safari doesn't give the most updated JRE version number - I found this out by displaying the value of the getJREs() function. I have 1.6.0_20 installed, which is displayed in every other browser, but Safari keeps saying that only 1.5.0 is currently installed. I've also tried using the createWebStartLaunchButtonEx() function and specifying '1.6.0' as the minimum version, but when I click the button nothing happens (in any browser). Any suggestions?

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• Should I start to use CSS 3 & HTML 5?

  - by LeonixSolutions

  I fear this may sound subjective, sorry. I am wondering how "safe" it is to use CSS3 & HTML5 in a commercial app. I really want the power that they give, but am obviously wary that they are not completely standardized. If it helps any I can probably enforce the use of Chrome as the browser; I can likely offer FireFox as an alternative. I personally do not want to let the user choose their own browser and can probably enforce my choice in a corporate environment which is already heavily biased towards Google. I suppose that if I can enforce a Chrome only policy & carefully test before release then my only worry is that some "behaviour" may change in future. Would you risk it, or would play safe (or go with an alternative, such as a Java app, forgetting the browser)?

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• sql jdbc getgeneratedkeys with mysql returns column "id" not found

  - by iamrohitbanga

  I want to retrieve the most recently updated value in the table using an insert query. these are the datatypes in my sql table. int(11) // primary key auto increment, not being assigned by sqlQuery varchar(30) timestamp // has a default value. but i am explicit assigning it using CURRENT_TIMESTAMP varchar(300) varchar(300) varchar(300) int(11) varchar(300) // java code statement.executeUpdate(sqlQuery, Statement.RETURN_GENERATED_KEYS); ResultSet rs = statement.getGeneratedKeys(); System.out.println("here: " + rs.getMetaData().getColumnCount()); System.out.println("here1: " + rs.getMetaData().getColumnName(1)); // none of the following 3 works System.out.println("id: " + rs.getInt(1)); System.out.println("id: " + rs.getInt("GENERATED_KEY")); System.out.println("id: " + rs.getInt("id")); for a bit of background see this

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• PgJDBC: "no suitable driver found" when following tutorial, why?

  - by Celeritas

  I'm writing a Java program that queries a PostgreSQL database. I'm following this example and have trouble here: connection = DriverManager.getConnection( "jdbc:postgresql://127.0.0.1:5432/testdb", "mkyong", "123456"); According to the JavaDoc for DriverManager the first string is "a database url of the form jdbc:subprotocol:subname. When I connect to the server I type in psql -h dataserv.abc.company.com -d app -U emp24 and give the password qwe123 (for example sake). What should the first argument of getConnection be? I've tried connection = DriverManager.getConnection( "jdbc:postgresql://dataserv.abc.company.com", "emp24", "qwe123"); and get the run time error: no suitable driver found. I've download JDBC4 Postgresql Driver, Version 9.2-1000.

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• Android XML file doesn't save

  - by Shane

  I'm writing a game with LibGDX, and I'm trying to save an XML file, but there's always an exception (java.io.FileNotFoundException: /data/Slugfest/teams/Team1.xml: open failed: ENOENT (No such file or directory)) when saving the file. This code saves the file. public void save() { try { TransformerFactory transformerFactory = TransformerFactory.newInstance(); Transformer transformer = transformerFactory.newTransformer(); DOMSource source = new DOMSource(doc); StreamResult result; if (Gdx.app.getType() == ApplicationType.Android) { result = new StreamResult(new File("/data/Slugfest/teams/" + name + ".xml")); } else { result = new StreamResult(new File(name + ".xml")); } transformer.transform(source, result); Gdx.app.log("Slugfest", "File saved."); } catch (TransformerException tfe) { Gdx.app.log("Slugfest", tfe.getLocalizedMessage()); } } My manifest file includes the WRITE/READ_EXTERNAL_STORAGE permissions, by the way.

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• ArrayList without repetition

  - by tuxou

  Hi i'm using arraylist in java and i need to add integers during 10 iteration (integer is got randomly from an array of integers named arrint) without any repetion: for (int i =0; i<10; ++i) array.add(integer); and then add in the same array 20 other integers for the same array of integer(arrint) during 20 iteration without repetion for (int i =0; i<10; ++i) array.add(integer); but repetition is permited between the 10 first integers and the 20 integers thank you

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• Is it a good idea to use only a key to encrypt an entire (small) filesystem?

  - by Fernando Miguélez

  This question comes as part of my doubts presented on a broader question about ideas implementing a small encrypted filesystem on Java Mobile phones (J2ME, BlackBerry, Android). Provided the litte feedback received, considering the density of the question, I decided to divide those doubts into small questions. So to sum up I plan to "create" an encrypted filesystem for for mobile phones (with the help of BoucyCastle or a subset of JCE), providing an API that let access to them in a transparent way. Encryption would be carried out on a file basis (not blocks). My question is this: Is it a good idea to use only a simmetric key (maybe AES-256) to encrypt all the files (they wouldn't be that many, maybe tens of them) and store this key in a keystore (protected by a pin) or would you rather encrypt each file with an on-the-fly generated key stored alongside each file, encrypting that key with the "master" key stored on the keystore? What are the benefits/drawbacks of each approach?

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• To "null" or not to "null" my class's attributes

  - by Helper Method

  When I write a class in Java, I like to initialize the attributes which are set to a default value directly and attributes which are set by the caller in the constructor, something like this: public class Stack<E> { private List<E> list; private size = 0; public Stack(int initialCapacity) { list = new ArrayList<E>(initialCapacity); } // remainder omitted } Now suppose I have a Tree class: public class Tree<E> { private Node<E> root = null; // no constructor needed, remainder omitted } Shall I set the root attribute to null, to mark that it is set to null by default, or omit the null value?

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• rewrite image URLs

  - by Don

  Hi, I'm writing a Maven plugin that merges CSS files together. So all the CSS files that match /foo/bar/*.css might get merged to /foo/merged.css. A concern is that in a file such as /foo/bar/baz.css there might be a property such as: background: url("images/pic.jpg") So when the file is merged into /foo/merged.css this will need to be changed to background: url("bar/images/pic.jpg") The recalculated URL obviously depends on 3 factors: original URL original CSS file location merged CSS file location Assuming that the original and merged CSS files are both on the same filesystem, is there a general formula (or Java library) that can be used to calculate the new url given these 3 inputs? Thanks, Don

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• Custom ArrayList serialization

  - by rayman

  Hi, i was trying to serialize an ArrayList which contacins custom objects. I`am serializing it in a servlet(server side), and deserialize at the client side. (using ObjectOutputStream,ObjectInputStream) it worked fine, when I work with ArrayList< String but when i tried it with ArrayList< MyObject i couldnt get any results in the client side, this is the exception: java.lang.ClassNotFoundException: web.MyObject *ofcourse that i have done this: MyObject implements Serializable ... MyObject contains only String fields in it. what have I done worng? Thanks, ray.

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• filter log file by defining regexes

  - by fmpdmb

  I have some HUGE log files (50Mb; ~500K lines) I need to start filtering some of the crap out of. The log files are being produced using log4j and have the basic pattern of: [log-level] date-time class etc, etc log-message I'm looking for a way that I can identify a regex start and regex end (or something similar) that will filter out the matching entries from the file so I can more easily wade through these massive files. I'm sure I could write a java program to accomplish this task, but I thought I'd ask the community before going down that path. Thanks in advance.

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• [Android] How do I load URL that requires login into variable?

  - by bebeTech

  I am trying to port my usage meter from a JavaScript Gadget (win) / Widget (OSX) to Android. Total newbie when comes to JAVA + Eclipse + Android 2.1 SDK. Essentially what I want to do is load a page, pass through a username and password and load the resulting page into a array that I can then run some regular expressions through. My code from JavaScript (I've replace the actual URL with a dummy one) is: xmlhttp.open("post","https://acme.com.au/your_account/index.php?function=login",false); xmlhttp.setRequestHeader("If-Modified-Since", "Sat, 1 Jan 2000 00:00:00 GMT"); xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); xmlhttp.send("check_username=" + username + "&password=" + password); I need to know the Android equivalent to the above please. I've played around with WebView but that loads the page in a web browser which isn't what I want.

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• When to stop following the advice of static code analysis?

  - by bananeweizen

  I do use static code analysis on a project with more than 100.000 lines of Java code for quite a while now. I started with Findbugs, which gave me around 1500 issues at the beginning. I fixed the most severe over time and started using additional tools like PMD, Lint4J, JNorm and now Enerjy. With the more severe issues being fixed, there is a huge number of low severity issues. How do you handle these low priority issues? Do you try fixing all of them? Or only in newly written code? Do you regularly disable certain rules? (I found that I do on nearly any of the available tools). And if you ignore or disable rules, do you document those? What do your managers say about "leaving some thousand low priority issues not fixed"? Do you use (multiple) tool specific comments in the code or is there any better way?

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