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• For a set of sql-queries, how do you determine which result-set contains a certain row?

  - by ManBugra

  I have a set of sql - queries: List<String> queries = ... queries[0] = "select id from person where ..."; ... queries[8756] = "select id from person where ..."; Each query selects rows from the same table 'person'. The only difference is the where-clause. Table 'person' looks like this: id | name | ... many other columns How can i determine which queries will contain a certain person in their subset? For example: List<Integer> matchingQueries = magicMethod(queries, [23,45]); The list obtained by 'magicMethod' filters all sql queries present in the list 'queries' (defined above) and returns only those that contain either the person with id 23 OR a person with id 45. Why i need it: I am dealing with an application that contains products and categories where the categories are sql queries that define which products belong to them (queries stored in a table also). Now i have a requirement where an admin has to see all categories an item belongs to immediately after the item was created. Btw, over 8.000 categories defined (so far, more to come). language and db: java && postgreSQL Thanks,

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• Unable to create a breakpoint in Eclipse and Tomcat

  - by Traroth

  Since yesterday, I get a strange error message when I start my Tomcat (6.0.35) under Eclipse Juno (build 20120614-1722): Among the things I tried in order to get rid of the error: Check in Preferences - Java - Compiler if all "Classfile Generation" checkboxes where checked. I did that for both general preferences and project preference Uncheck them, build, check them build again (found on another question) Add org.eclipse.jdt.core.compiler.debug.lineNumber=generate to my .settings/org.eclipse.jdt.core.prefs file Use a new CVS checkout (same symptoms) And now, I don't know what to do anymore. The problem is really stopping me from get anything done. I can't work anymore. Crazy is: the problem doesn't happen on every class, only on some of them. Neither does it happen on my other Eclipse projects. And it didn't happen before yesterday, even if I can't remeber having done anything weird. Actually, I have never seen a problem like this in almost 10 years I'm using Eclipse... If you have any idea, I would be really grateful... Edit: I also tried to ignore the message and go on with my tests: If I create another breakpoint upstream from my problematic class, when I enter this problematic class, it tries to open a $Proxy132 class, which means it actually opens an empty page, with a source not found message

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• Streaming content to JSF UI

  - by Mark Lewis

  Hello, I was quite happy with my JSF app which read the contents of MQ messages received and supplied them to the UI like this: <rich:panel> <snip> <rich:panelMenuItem label="mylabel" action="#{MyBacking.updateCurrent}"> <f:param name="current" value="mylog.log" /> </rich:panelMenuItem> </snip> </rich:panel> <rich:panel> <a4j:outputPanel ajaxRendered="true"> <rich:insert content="#{MyBacking.log}" highlight="groovy" /> </a4j:outputPanel> </rich:panel> and in MyBacking.java private String logFile = null; ... public String updateCurrent() { FacesContext context=FacesContext.getCurrentInstance(); setCurrent((String)context.getExternalContext().getRequestParameterMap().get("current")); setLog(getCurrent()); return null; } public void setLog(String log) { sendMsg(log); msgBody = receiveMsg(moreargs); logFile = msgBody; } public String getLog() { return logFile; } until the contents of one of the messages was too big and tomcat fell over. Obviously, I thought, I need to change the way it works so that I return some form of stream so that no one object grows so big that the container dies and the content returned by successive messages is streamed to the UI as it comes in. Am I right in thinking that I can replace the work I'm doing now on a String object with a BufferedOutputStream object ie no change to the JSF code and something like this changing at the back end: private BufferedOutputStream logFile = null; public void setLog(String log) { sendMsg(args); logFile = (BufferedOutputStream) receiveMsg(moreargs); } public String getLog() { return logFile; }

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• Lost in dates and timezones

  - by Sebastien

  I'm working on an application that stores conferences with their start and end date. Up until now, I was developing in Belgium and my server is in France, so everything is in the same timezone, no problem. But today, I'm in San Francisco, my server is in France and I noticed I have a bug. I'm setting dates from a Flex client (ActionScript automatically adapts date display according to client local timezone, which is GMT-8 for me today. My server runs on Hibernate and MySQL in France (GMT+1). So when I look at my database using phpMyAdmin, I see a date set to "2010-06-07 00:00:01" but in my Flex client it displays "2010-06-06 15:00:01". Ultimately, what I want is that the dates are displayed in the local timezone of the event, which is the date I set it to. So when I'm in Belgium and I set the start date of an event to be "2010-06-07 00:00:01" I want to retrieve it that way. But I'm lost as to what layer adapts what. Is timezone stored in DATETIME MySQL columns (I can't see it in MySQL)? Does Hibernate to anything to it when it transfers it to java.lang.Date that has Timezone information? And ultimately, what is the best way to solve this mess?

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• Why I get this error in CXF

  - by Milan

  I want to make dynamic web service invoker in JSF with CXF. But when I load this simple code I get error. The code: JaxWsDynamicClientFactory dcf = JaxWsDynamicClientFactory.newInstance(); Client client = dcf.createClient("http://ws.strikeiron.com/IPLookup2?wsdl"); The error: No Factories configured for this Application. This happens if the faces-initialization does not work at all - make sure that you properly include all configuration settings necessary for a basic faces application and that all the necessary libs are included. Also check the logging output of your web application and your container for any exceptions! If you did that and find nothing, the mistake might be due to the fact that you use some special web-containers which do not support registering context-listeners via TLD files and a context listener is not setup in your web.xml. A typical config looks like this; org.apache.myfaces.webapp.StartupServletContextListener Caused by: java.lang.IllegalStateException - No Factories configured for this Application. This happens if the faces-initialization does not work at all - make sure that you properly include all configuration settings necessary for a basic faces application and that all the necessary libs are included. Also check the logging output of your web application and your container for any exceptions! If you did that and find nothing, the mistake might be due to the fact that you use some special web-containers which do not support registering context-listeners via TLD files and a context listener is not setup in your web.xml. A typical config looks like this; org.apache.myfaces.webapp.StartupServletContextListener Any Idea how to solve the problem?

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• Way to store a large dictionary with low memory footprint + fast lookups (on Android)

  - by BobbyJim

  I'm developing an android word game app that needs a large (~250,000 word dictionary) available. I need: reasonably fast look ups e.g. constant time preferable, need to do maybe 200 lookups a second on occasion to solve a word puzzle and maybe 20 lookups within 0.2 second more often to check words the user just spelled. EDIT: Lookups are typically asking "Is in the dictionary?". I'd like to support up to two wildcards in the word as well, but this is easy enough by just generating all possible letters the wildcards could have been and checking the generated words (i.e. 26 * 26 lookups for a word with two wildcards). as it's a mobile app, using as little memory as possible and requiring only a small initial download for the dictionary data is top priority. My first naive attempts used Java's HashMap class, which caused an out of memory exception. I've looked into using the SQL lite databases available on android, but this seems like overkill. What's a good way to do what I need?

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• Searching in an Arraylist

  - by Puchatek

  Currently I have two classes. A Classroom class and a School class. I would like to write a method in the School class public void showClassRoomDetails which would find the classroom details by only using the teacherName. e.g. teacherName = Daniel className = Science teacherName = Bob className = Maths so when I input Bob, it would print out Bob and Maths many, thanks public class Classroom { private String classRoomName; private String teacherName; public void setClassRoomName(String newClassRoomName) { classRoomName = newClassRoomName; } public String returnClassRoomName() { return classRoomName; } public void setTeacherName(String newTeacherName) { teacherName = newTeacherName; } public String returnTeacherName() { return teacherName; } } import java.util.ArrayList; public class School { private ArrayList<Classroom> classrooms; private String classRoomName; private String teacherName; public School() { classrooms = new ArrayList<Classroom>(); } public void addClassRoom(Classroom newClassRoom, String theClassRoomName) { classrooms.add(newClassRoom); classRoomName = theClassRoomName; } public void addTeacherToClassRoom(int classroomId, String TeacherName) { if (classroomId < classrooms.size() ) { classrooms.get(classroomId).setTeacherName(TeacherName); } } public void showClassRoomDetails { //loop System.out.println(returnClassRoomName); System.out.println(returnTeacherName); } }

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• What is the correct stage to use for Google Guice in production in an application server?

  - by Yishai

  It seems like a strange question (the obvious answer would Production, duh), but if you read the java docs: /** * We want fast startup times at the expense of runtime performance and some up front error * checking. */ DEVELOPMENT, /** * We want to catch errors as early as possible and take performance hits up front. */ PRODUCTION Assuming a scenario where you have a stateless call to an application server, the initial receiving method (or there abouts) creates the injector new every call. If there all of the module bindings are not needed in a given call, then it would seem to have been better to use the Development stage (which is the default) and not take the performance hit upfront, because you may never take it at all, and here the distinction between "upfront" and "runtime performance" is kind of moot, as it is one call. Of course the downside of this would appear to be that you would lose the error checking, causing potential code paths to cause a problem by surprise. So the question boils down to are the assumptions in the above correct? Will you save performance on a large set of modules when the given lifetime of an injector is one call?

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• Open source real life license examples: yours or others

  - by donpal

  I'm aware of the usual list of open source licenses, so I'm not even going to list it here. What I'd like to ask is about your open source projects (whether out or planned for the future), and why you're planning to choose a certain license over the other. Basically say I went for X license because I wanted Y and that other license didn't provide it for me. I understand that the language itself can make a difference in the choice of license: interpreted languages like PHP vs. compiled languages like Java. I'm mostly interested in hearing about PHP projects, but of course additional insights are welcome. You may even have chosen that particular language for a licensing reason. Ideally I want to hear answers from people who were involved in the actual project (i.e. your own project), because that usually means you've put some thought into the license yourself and understand the implications of that license. But examples of existing projects that aren't your own are OK. Please just say why you think that license was good/bad for them. But first-hand experience is preferred. Looking forward to hearing some informative input.

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• Running single test class or group with Surefire and TestNG

  - by Slartibartfast

  I want to run single test class from command line using Maven and TestNG Things that doesn't work: mvn -Dtest=ClassName test I have defined groups in pom.xml, and this class isn't in one of those groups. So it got excluded on those grounds. mvn -Dgroups=skipped-group test mvn -Dsurefire.groups=skipped-group test when config is <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-surefire-plugin</artifactId> <version>2.7.1</version> <configuration> <groups>functest</groups> </configuration> </plugin> Parameters work fine in there are no groups defined in pom.xml. Similarly, when surefire is configured with <configuration> <includes> <include>**/*UnitTest.java</include> </includes> </configuration> I can add another test with -Dtest parameter, but cannot add group. In any combination, I can narrow down tests to be executed with groups, but not expand them. What's wrong with my configuration? Is there a way to run a single test or group outside of those defined in pom.xml? Tried on Ubuntu 10.04 with Maven 2.2.1, TestNG 5.14.6 and Surefire 2.7.1

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• Uva's 3n+1 problem

  - by dmindreader

  I'm solving Uva's 3n+1 problem and I don't get why the judge is rejecting my answer. The time limit hasn't been exceeded and the all test cases I've tried have run correctly so far. import java.io.*; public class NewClass{ /** * @param args the command line arguments */ public static void main(String[] args) throws IOException { int maxCounter= 0; int input; int lowerBound; int upperBound; int counter; int numberOfCycles; int maxCycles= 0; int lowerInt; BufferedReader consoleInput = new BufferedReader(new InputStreamReader(System.in)); String line = consoleInput.readLine(); String [] splitted = line.split(" "); lowerBound = Integer.parseInt(splitted[0]); upperBound = Integer.parseInt(splitted[1]); int [] recentlyused = new int[1000001]; if (lowerBound > upperBound ) { int h = upperBound; upperBound = lowerBound; lowerBound = h; } lowerInt = lowerBound; while (lowerBound <= upperBound) { counter = lowerBound; numberOfCycles = 0; if (recentlyused[counter] == 0) { while ( counter != 1 ) { if (recentlyused[counter] != 0) { numberOfCycles = recentlyused[counter] + numberOfCycles; counter = 1; } else { if (counter % 2 == 0) { counter = counter /2; } else { counter = 3*counter + 1; } numberOfCycles++; } } } else { numberOfCycles = recentlyused[counter] + numberOfCycles; counter = 1; } recentlyused[lowerBound] = numberOfCycles; if (numberOfCycles > maxCycles) { maxCycles = numberOfCycles; } lowerBound++; } System.out.println(lowerInt +" "+ upperBound+ " "+ (maxCycles+1)); } }

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• What good open source programs exist for fuzzing popular image file types?

  - by JohnnySoftware

  I am looking for a free, open source, portable fuzzing tool for popular image file types that is written in either Java, Python, or Jython. Ideally, it would accept specifications for the fuzzable fields using some kind of declarative constraints. Non-procedural grammar for specifying constraints are greatly preferred. Otherwise, might as well write them all in Python or whatever. Just specifying ranges of valid values or expressions for them. Ideally, it would support some kind of generative programming to export the fuzzer into various programming languages to suit cases where more customization was required. If it supported a direct-manipulation GUI for controlling parameter values and ranges, that would be nice too. The file formats that should be supported are: GIF JPEG PNG So basically, it should be sort of a toolkit consisting of ready-to-run utility, a framework or library, and be capable of generating the fuzzed files directly as well as from programs it generates. It needs to be simple so that test images can be created quickly. It should have a batch capability for creating a series of images. Creating just one at a time would be too painful. I do not want a hacking tool, just a QA tool. Basically, I just want to address concerns that it is taking too long to get commonplace image rendering/parsing libraries stable and trustworthy.

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• How to get components from a JFrame with a GridLayout?

  - by NlightNfotis

  I have a question about Java and JFrame in particular. Let's say I have a JFrame that I am using with a GridLayout. Supposing that I have added JButtons in the JFrame, how can I gain access to the one I want using it's position (by position, I mean a x and a y, used to define the exact place on the Grid). I have tried several methods, for instance getComponentAt(int x, int y), and have seen that those methods do not work as intended when combined with GridLayout, or at least don't work as intended in my case. So I tried using getComponent(), which seems fine. The latest method, that seems to be on a right track for me is (assuming I have a JFrame with a GridLayout with 7 rows and 7 columns, x as columns, y as rows): public JButton getButtonByXAndY(int x, int y) { return (JButton) this.getContentPane().getComponent((y-1) * 7 + x); } Using the above, say I want to get the JButton at (4, 4), meaning the 25th JButton in the JFrame, I would index through the first 21 buttons at first, and then add 4 more, finally accessing the JButton I want. Problem is this works like that in theory only. Any ideas? P.S sorry for linking to an external website, but stack overflow won't allow me to upload the image, because I do not have the required reputation.

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• Generate Android Soft Key via Java Code

  - by Shubh

  How can I generate Soft Key using Java Code instead generate using XML, so i can set my own ASCII value array.

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• Connect.registerUsers - Need helping creating array for accounts param

  - by mw_javaguy

  I keep getting the following error when I try to invoke the Facebook REST API Call: Connect.registerUsers Error Code: 100 - param accounts must be an array JSON based response (from Facebook): {"error_code":100,"error_msg":"param accounts must be an array.","request_args": [{"key":"accounts","value":"{email_hash:5232156322_55ddgvc3db5ddcf218049dd564da2x06}"}, {"key":"api_key","value":"23b2c4c6a23445fbffssf8aab96a5e5"}, {"key":"format","value":"JSON"},{"key":"method","value":"Connect.registerUsers"},{"key":"sig","value":"3sd54153a31382fa6e72eecf3c57d7c9"},{"key":"v","value":"1.0"}],"message":"Unknown exception","code":0} I set up the Java code to invoke the REST end point using HttpClient like this: String API_KEY = "23b2c4c6a23445fbffssf8aab96a5e5"; String toConnectRegisterUsersSignature = "accounts=" + "{email_hash:" + emailHash + "}" + "api_key=" + API_KEY + "format=JSON" + "method=Connect.registerUsers" + "v=1.0" + "0c786155bd3cxe8228d924542da5gf2"; String connectRegisterUsersSignature = SimpleMd5.MD5(toConnectRegisterUsersSignature); NameValuePair[] connectRegisterUsersParameters = { new NameValuePair("accounts", "{email_hash:" + emailHash + "}"), new NameValuePair("api_key", API_KEY), new NameValuePair("format", "JSON"), new NameValuePair("method", "Connect.registerUsers"), new NameValuePair("sig", connectRegisterUsersSignature), new NameValuePair("v", "1.0") }; Tried the following combinations and I still get the same error! Signature: "accounts=" + "[email_hash=" + emailHash + "]" new NameValuePair("accounts", "[email_hash=" + emailHash + "]") Signature: "accounts=" + "email_hash[" + emailHash + "]" new NameValuePair("accounts", "email_hash[" + emailHash + "]") Signature: "accounts=" + "email_hash(" + emailHash + ")" new NameValuePair("accounts", "email_hash(" + emailHash + ")") Signature: "accounts=" + "[email_hash=" + emailHash + "]" new NameValuePair("accounts", "[email_hash=" + emailHash + "]") Signature: "accounts=" + "email_hash=" + emailHash new NameValuePair("accounts", "email_hash=" + emailHash) Signature: "accounts=" + "[{email_hash:" + emailHash + "}]" new NameValuePair("accounts", "[{email_hash:" + emailHash + "}]"), Does anyone know how to construct this array that the response is requesting? Happy programming and thank you for taking the time to read this.

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• What is a reasonable OSGi development workflow?

  - by levand

  I'm using OSGi for my latest project at work, and it's pretty beautiful as far as modularity and functionality. But I'm not happy with the development workflow. Eventually, I plan to have 30-50 separate bundles, arranged in a dependency graph - supposedly, this is what OSGi is designed for. But I can't figure out a clean way to manage dependencies at compile time. Example: You have bundles A and B. B depends on packages defined in A. Each bundle is developed as a separate Java project. In order to compile B, A has to be on the javac classpath. Do you: Reference the file system location of project A in B's build script? Build A and throw the jar into B's lib directory? Rely on Eclipse's "referenced projects" feature and always use Eclipse's classpath to build (ugh) Use a common "lib" directory for all projects and dump the bundle jars there after compilation? Set up a bundle repository, parse the manifest from the build script and pull down the required bundles from the repository? No. 5 sounds the cleanest, but also like a lot of overhead.

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• JVM to ignore certificate name mismatch

  - by Heavy Bytes

  I know there were a lot of questions/answers about how to ignore SSL error in the code. On our dev region dev.domain.tld we have configured a app server over SSL. The certificate that is displayed is for somedev.domain.tld. There is no way to change the certificate, it will always be a domain mismatch. So when I deploy a web-service to https://dev.domain.tld and try to connect/call my webservice I get an exception: Caused by: java.security.cert.CertificateException: No name matching dev.domain.tld found And I have the somedev.domain.tld CERT in my trust store. Now, I saw a lot of samples how to change that in the code (using a Trust Manager that accepts all domains), but how do I specify to the JVM to ignore the domain mismatch when connecting to the server? Is there a -Djavax.net.ssl argument or something? Thank you! UPDATE: Or, since I am using Spring-WS, is there a way to set some property in Spring for that? (WebServiceTemplate) UPDATE I guess I'll have to do use something from Spring Security: http://static.springsource.org/spring-ws/sites/1.5/reference/html/security.html

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• Address family not supported by protocol exception

  - by srg

  I'm trying to send a couple of values from an android application to a web service which I've setup. I'm using Http Post to send them but when I run the application I get the error- request time failed java.net.SocketException: Address family not supported by protocol. I get this while debugging with both the emulator as well as a device connected by wifi. I've already added the internet permission using: <uses-permission android:name="android.permission.INTERNET" /> This is the code i'm using to send the values void insertData(String name, String number) throws Exception { String url = "http://192.168.0.12:8000/testapp/default/call/run/insertdbdata/"; HttpClient client = new DefaultHttpClient(); HttpPost post = new HttpPost(url); try { List<NameValuePair> params = new ArrayList<NameValuePair>(2); params.add(new BasicNameValuePair("a", name)); params.add(new BasicNameValuePair("b", number)); post.setEntity(new UrlEncodedFormEntity(params)); HttpResponse response = client.execute(post); }catch(Exception e){ e.printStackTrace(); } Also I know that my web service work fine because when I send the values from an html page it works fine - <form name="form1" action="http://192.168.0.12:8000/testapp/default/call/run/insertdbdata/" method="post"> <input type="text" name="a"/> <input type="text" name="b"/> <input type="submit"/> I've seen questions of similar problems but haven't really found a solution. Thanks

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• Android Layout + Programming

  - by MD

  I'm trying to create a "scrollable" layout in Android. Even using developers.android.com, though, I feel a little bit lost at the moment. I'm somewhat new to Java, but not so much that I feel I should be having these issues--being new to Android is the bigger problem right now. The layout I'm trying to create should scroll in a sort of a "grid". I THINK what I'm looking for is the Gallery view, but I'm really lost as to how to implement it at the moment. I want it to "snap" to center the frame, like in the actual Gallery application. Essentially, if I had a photo gallery of 9 pictures, the idea is to scroll between them up/down AND side to side, in a 3x3 manner. Doesn't need to dynamically adjust, or anything like that, I just want a grid I can scroll through. I'm also not asking for anyone to give me explicit code for it--I'm trying to learn, more than anything. But pointing me in the right direction for helpful layout programming resources would be greatly appreciated, and confirming if it's a Gallery view I'm looking for would also be really helpful. Thanks in advance.

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• Within an aray of objects can one create a new instance of an object at an index?

  - by David

  Here's the sample code: class TestAO { int[] x; public TestAO () { this.x = new int[5] ; for (int i = 0; i<x.length; i++) x[i] = i; } public static void main (String[]arg) { TestAO a = new TestAO (); System.out.println (a) ; TestAO c = new TestAO () ; c.x[3] = 35 ; TestAO[] Z = new TestAO[3] ; Z[0] = a ; Z[1] = (TestAO b = new TestAO()) ; Z[2] = c ; } } When i try to compile this i get an error message at the line Z[1] which reads as follows: TestAO.java:22: ')' expected Z[1] = (TestAO b = new TestAO()) ; ^ What i'm trying to do here is create an instance of the object TestAO that i want to be in that index within the assignment of the value at that index instead of creating the instance of the object outside of the array like i did with a. Is this legal and i'm just making some syntax error that i can't see (thus causing the error message) or can what i'm trying to do just not be done?

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• How to display panels with component in frame

  - by terence6

  Why my JFrame 'frame' is diplaying empty window, when it should give me 3 menu buttons and my own painted JComponent below ? What am I missing here ? import java.awt.*; import javax.swing.*; public class Eyes extends JFrame { public static void main(String[] args) { final JFrame frame = new JFrame("Eyes"); frame.setPreferredSize(new Dimension(450, 300)); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel players = new JPanel(new GridLayout(1, 3)); players.add(new JButton("Eyes color")); players.add(new JButton("Eye pupil")); players.add(new JButton("Background color")); JPanel eyes = new JPanel(); eyes.add(new MyComponent()); JPanel content = new JPanel(); content.setLayout(new BoxLayout(content, BoxLayout.Y_AXIS)); content.add(players); content.add(eyes); frame.getContentPane(); frame.pack(); frame.setVisible(true); } } class MyComponent extends JComponent { public MyComponent(){ } @Override public void paint(Graphics g) { int height = 120; int width = 120; Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON); BasicStroke bs = new BasicStroke(3.0f); g2d.setStroke(bs); g2d.setColor(Color.yellow); g2d.fillOval(200, 200, height, width); g2d.setColor(Color.black); g2d.drawOval(60, 60, height, width); } }

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• Android shared library which is not JNI based

  - by Mondain

  I am developing a library for Android applications which does not use native code (JNI). I have tried suppling the library as an external jar in my Android projects but this method does not include the library contents in the apk and thus throws class not found errors when run in the emulator or device. I have also tried creating the library as an Android project in itself and this does work, but only for public static properties (not methods). With the library and application both being in separate apk's I can see that the VM notices references to the library and can read some properties, but when an attempt to instantiate a class in the library is executed I get class not found even though I can read the public static properties from it (very frustrating!!). I realize that Davlik byte code is not the same as Java byte code but I am having trouble even finding good information about how to solve what would seem to be a very simple issue in Android. I am looking into the old PlatformLibrary stuff right now but I am not convinced this will work either since the sample has been removed from the Android site :( So help me out if you can, if I find the answer before this happens I will share it. viva la Android!

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• JPA/Hibernate Parent/Child relationship

  - by NubieJ

  Hi I am quite new to JPA/Hibernate (Java in general) so my question is as follows (note, I have searched far and wide and have not come across an answer to this): I have two entities: Parent and Child (naming changed). Parent contains a list of Children and Children refers back to parent. e.g. @Entity public class Parent { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "PARENT_ID", insertable = false, updatable = false) private int id; /* ..... */ @OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", nullable = true) private Set<child> children; /* ..... */ } @Entity public class Child { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "CHILD_ID", insertable = false, updatable = false) private int id; /* ..... */ @ManyToOne(cascade = { CascadeType.REFRESH }, fetch = FetchType.EAGER, optional = false) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID") private Parent parent; /* ..... */ } I want to be able to do the following: Retrieve a Parent entity which would contain a list of all its children (List), however, when listing Parent (getting List, it of course should omit the children from the results, therefore setting FetchType.LAZY. Retrieve a Child entity which would contain an instance of the Parent entity. Using the code above (or similar) results in two exceptions: Retrieving Parent: A cycle is detected in the object graph. This will cause infinitely deep XML... Retrieving Child: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxxxxxxxxxx, no session or session was closed When retrieving the Parent entity, I am using a named query (i.e. calling it specifically) @NamedQuery(name = "Parent.findByParentId", query = "SELECT p FROM Parent AS p LEFT JOIN FETCH p.children where p.id = :id") Code to get Parent (i.e. service layer): public Parent findByParentId(int parentId) { Query query = em.createNamedQuery("Parent.findByParentId"); query.setParameter("id", parentId); return (Parent) query.getSingleResult(); } Why am I getting a LazyInitializationException event though the List property on the Parent entity is set as Lazy (when retrieving the Child entity)?

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• How do I check if a variable has been initialized

  - by Javier Parra

  First of all, I'm fairly new to Java, so sorry if this question is utterly simple. The thing is: I have a String[] s made by splitting a String in which every item is a number. I want to cast the items of s into a int[] n. s[0] contains the number of items that n will hold, effectively s.length-1. I'm trying to do this using a foreach loop: int[] n; for(String num: s){ //if(n is not initialized){ n = new int[(int) num]; continue; } n[n.length] = (int) num; } Now, I realize that I could use something like this: int[] n = new int[(int) s[0]]; for(int i=0; i < s.length; i++){ n[n.length] = (int) s[i]; } But I'm sure that I will be faced with that "if n is not initialized initialize it" problem in the future.

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• Parameterized SPARQL query with JENA

  - by sandra

  I'm trying to build a small semantic web application using Jena framework, JSP and JAVA. I have a remote SPARQL endpoint and I've already written a simple query which works fine but now I need to use some parameters. Here is my code so far: final static String serviceEndpoint = "http://fishdelish.cs.man.ac.uk/sparql/"; String comNameQuery = "PREFIX fd: <http://fishdelish.cs.man.ac.uk/rdf/vocab/resource/> " + "SELECT ?name ?language ?type" + "WHERE { ?nameID fd:comnames_ComName ?name ;" + "fd:comnames_Language ?language ;" + "fd:comnames_NameType ?type ." + "}"; Query query = QueryFactory.create(comNameQuery); QueryExecution qe = QueryExecutionFactory.sparqlService(serviceEndpoint,query); try { ResultSet rs = qe.execSelect(); if ( rs.hasNext() ) { System.out.println(ResultSetFormatter.asText(rs)); } } catch(Exception e) { System.out.println(e.getMessage()); } finally { qe.close(); } What I want to do is to parameterized ?name. I'm new to Jena and I'm not really sure how to use parameters in a SPARQL query. I would appreciate it if someone could help me with this.

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