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• Embedded Java Databases for Large Data Sets

  - by ExAmerican

  I would like to port a PHP/MySQL-based client/server application to be a standalone desktop application written in Java. The database has grown to be fairly large, with several tables with hundreds of thousands of rows. I expect these could grow to over a million entries for certain tables. What embedded database would best handle this? HSQLDB and Sqlite seem to be the obvious choices, though I'm guessing there are others out there as well. My main priorities are the ability to perform queries on large amounts of data efficiently (this thread seems to confirm Sqlite can handle this) and the ease with which I can import old data from MySQL (I remember HSQLDB being kind of a pain for that). Note: I am aware that similar questions comparing embedded databases have been posted before (for example here and here) but as my priorities differ somewhat from most applications considering the large data migration I thought it justified a new question.

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• Use of class definitions inside a method in Java

  - by Bragaadeesh

  Hi public class TestClass { public static void main(String[] args) { TestClass t = new TestClass(); } private static void testMethod(){ class TestMethodClass{ int a; int b; int c; } TestMethodClass testMethodClass = new TestMethodClass(); } } I found out that the above piece of code is perfectly legal in Java. I have the following questions. What is the use of ever having a class definition inside a method? Will a class file be generated for TestMethodClass Its hard for me to imagine this concept in an Object Oriented manner. Having a class definition inside a behavior. Probably can someone tell me with equivalent real world examples. Thanks

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• Java : VolatileImage slower than BufferedImage.

  - by Norswap

  I'm making a game in java and in used BufferedImages to render content to the screen. I had performance issues on low end machines where the game is supposed to run, so I switched to VolatileImage which are normally faster. Except they actually slow the whole thing down. The images are created with GraphicsConfiguration.createCompatibleVolatileImage(...) and are drawn to the screen with Graphics.drawImage(...) (follow link to see which one specifically). They are drawn upon a Canvas using double buffering. Does someone has an idea of what is going wrong here ?

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• On demand population of dropdown menu Java/Swing?

  - by Cookie Monster

  When I code a popup menu, I can check the mouse event and then before calling show() prepare the menu. Now I want a similar functionality for drop down menus, that live in the menu bar. For example I have the following menu bar layout: Menu 1 MenuItem 1.1 MenuItem 1.1.1 MenuItem 1.1.2 .. MenuItem 1.1.n Menu 2 Basically I want to generate the list MenuItem 1.1.1, MenuItem 1.1.2, ..., MenuItem 1.1.n dynamically when the drop down menu is invoked and before it is shown. How could I do this in Java/Swing? Best Regards

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• Web Development In Java Using Netbeans

  - by GigaPr

  Hi I am trying to implement a web application(university project) in java using the following Frameworks Spring Dependency Injection Spring AOP (Logging and Transaction Management) Spring DAO JDBC or HIBERNATE Spring MVC Log4J I create a new Web Application in Netbeans and it gives me a bunch of Files and folders by default. Could anyone explain me what are the files ? Where shall i put the code for the data access layer and business Logic? Or where can i found a basic tutorial to get started(with data access layer, business layer and possibly code example)? Thanks

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• outlook calendar connectivity with java web service

  - by Isisagate

  We currently have a java/jsp online web service that includes it's own custom calendar. I am trying to do some research into the possibility of connecting it to a users outlook. Our basic needs that are most simple is some way to sent the person a meeting request that can be added to their outlook from our service. I know the ideal solution is to sync back and forth but simply being able to import the data from our calendar into someone's outlook would be sufficient. Does anyone have any resources they can point me to that might help with information gathering, or any example/comments?

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• How do I instantiate Class Dynamically in Java?

  - by kunjaan

  I have the class name stored in a property file. I know that the classes store will implement IDynamicLoad. How do I instantiate the class dynamically? Right now I have Properties foo = new Properties(); foo.load(new FileInputStream(new File("ClassName.properties"))); String class_name = foo.getProperty("class","DefaultClass"); //IDynamicLoad newClass = Class.forName(class_name).newInstance(); Does the newInstance only load compiled .class files? How do I load a Java Class that is not compiled?

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• What is/are the Scala way(s) to implement this Java "byte[] to Hex" class

  - by nicerobot

  I'm specifically interested in Scala (2.8) techniques for building strings with formats as well as interesting ways to make such a capability easily accessible where it's useful (lists of bytes, String, ...?).. public class Hex { public static String valueOf (final byte buf[]) { if (null == buf) { return null; } final StringBuilder sb = new StringBuilder(buf.length * 2); for (final byte b : buf) { sb.append(String.format("%02X", b & 0xff)); } return sb.toString(); } public static String valueOf (final Byteable o) { return valueOf(o.toByteArray()); } } This is only a learning exercise (so the utility and implementation of the Java isn't a concern.) Thanks

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• strange bug - how to pause a java program?

  - by TerraNova993

  I'm trying to: display a text in a jLabel, wait for two seconds, then write a new text in the jLabel this should be simple, but I get a strange bug: the first text is never written, the application just waits for 2 seconds and then displays the final text. here is the example code: private void testButtonActionPerformed(java.awt.event.ActionEvent evt) { displayLabel.setText("Clicked!"); // first method with System timer /* long t0= System.currentTimeMillis(); long t1= System.currentTimeMillis(); do{ t1 = System.currentTimeMillis(); } while ((t1 - t0) < (2000)); */ // second method with thread.sleep() try { Thread.currentThread().sleep(2000); } catch (InterruptedException e) {} displayLabel.setText("STOP"); } with this code, the text "Clicked!" is never displayed. I just get a 2 seconds - pause and then the "STOP" text. I tried to use System timer with a loop, or Thread.sleep(), but both methods give the same result.

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• How to get value from Java object

  - by JSF User

  I have this Java object private List<NewAccountObj> dataList; public class NewAccountObj { private int userid; public NewAccountObj(int userid) { this.userid = userid; } public int getUserid() { return userid; } public void setUserid(int userid) { this.userid = userid; } public List<NewAccountObj> getdataList() { return dataList; } What is the proper way to access a value from the object? Is this correct? <h:inputText id="userid" value="#{NewAccountController.dataList.userid}" validator="#{ValidatorAccountController.validateUserID}" autocomplete="off"> <f:ajax event="blur" render="useridvalidator" /> </h:inputText> Is there any other solution?

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• JAVA bytecode optimization

  - by Idob

  This is a basic question. I have code which shouldn't run on metadata beans. All metadata beans are located under metadata package. Now, I use reflection API to find out whether a class is located in the the metadata package. if (newEntity.getClass().getPackage().getName().contains("metadata")) I use this If in several places within this code. The question is: Should I do this once with: boolean isMetadata = false if (newEntity.getClass().getPackage().getName().contains("metadata")) { isMetadata = true; } C++ makes optimizations and knows that this code was already called and it won't call it again. Does JAVA makes optimization? I know reflection API is a beat heavy and I prefer not to lose expensive runtime.

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• How to implement a unit converter in java

  - by Mohit Deshpande

  How could I possibly implement a unit converter in Java??? I was thinking of having a abstract base class: public abstract class Unit { ... public void ConvertTo(Unit unit); } Then having each class like Meter Kilometer Inch Centimeter Millimeter ... derive from that base Unit class. All the units of length would be in a package called com.unitconverter.distance, then a package, com.unitconverter.energy, for energy etc. etc. So is this the best way to implement a unit converter? Or is there a better or more easier way?

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• Java Authenticator on a per connection basis?

  - by Martijn Laarman

  I'm building an Eclipse plugin that talks to a REST interface which uses Basic Authentication. When the authentication fails I would like to popup my plugin's settings dialog and retry. Normally I could use the static Authenticator.setDefault() to setup an authenticator for all HttpURLConnection's for this, but since I am writing a plugin I don't want to overwrite Eclipse's default Authenticator (org.eclipse.ui.internal.net.auth); I thought of setting my custom Authenticator before loading and putting Eclipse's default back afterwards, but I imagine this will cause all sorts of race issues with multithreading so I quickly lost that notion. Google searches yield all sorts of results basically telling me it's not possible: The Java URLConnection API should have a setAuthenticator(Authenticator) method for making it easier to use this class in multi-threaded context where authentication is required. Source If applications contains few third party plugins and each plugin use its own Authenticator what we should do? Each invocation of "Authenticator.setDefault()" method rewrite previously defined Authenticator... Source Are there any different approaches that might help me overcome this issue?

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• Question marks in Java generics.

  - by gnucom

  I tried to make sure this wasn't a duplicate post, sorry if I was blind. This is a small snippet of code taken from some of the examples that accompany the Stanford Parser. I've been developing in Java for about 4 years, but have never had a very strong understanding of what this style of code is supposed to indicate. List<? extends HasWord> wordList = toke.tokenize(); I'm not worried about the details of the code. What I'm confusing about is what exactly the generic expression is supposed to convey, in English. Can someone explain this to me? Thanks!

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• Java - Set Color by switch case function

  - by user369150

  I want to set the color of the TextView by the function getcolorss. I tried a lot of different ways but i cant get in it. Please help me i think the solution is easy. import java.awt.*; import android.graphics.Color; public class test extends Activity { TextView text1 = (TextView) findViewById(R.id.text1); text1.setTextColor(getcolorss(1)); public Color getcolorss(int x) { switch(x) { case 1: return Color.BLUE; case 2: return Color.RED; } } }

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• Java PreparedStatement Throws MySQLSyntaxErrorException

  - by sqlBugs

  I have the following Java code: String query = "Select 1 from myTable where name = ? and age = ?"; PreparedStatement stmt = conn.prepareStatement(query); stmt.setString(1, name); stmt.setInt(2, age); ResultSet rs = stmt.executeQuery(); Whenever I run the above code, it throws an exception on line 2 (where the PreparedStatement is declared): Error 0221202: SQLException = com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '? AND age = ?' at line 1 Does anyone have any suggestions about what I am doing wrong? Thanks!

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• Print number series in java

  - by user1898282

  I have to print the series shown below in java: ***1*** **2*2** *3*3*3* 4*4*4*4 My current implementation is: public static void printSeries(int number,int numberOfCharsinEachLine){ String s="*"; for(int i=1;i<=number;i++){ int countOfs=(numberOfCharsinEachLine-(i)-(i-1))/2; if(countOfs<0){ System.out.println("Can't be done"); break; } for(int j=0;j<countOfs;j++){ System.out.print(s); } System.out.print(i); for(int k=1;k<i;k++){ System.out.print(s); System.out.print(i); } for(int j=0;j<countOfs;j++){ System.out.print(s); } System.out.println(); } } But there are lot of for loops, so I'm wondering whether this can be done in a better way or not?

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• Method to concatenate 2 Strings in Java

  - by GooF

  I have a method in Java that concatenates 2 Strings. It currently works correctly, but I think it can be written better. public static String concat(String str1, String str2) { String rVal = null; if (str1 != null || str2 != null) { rVal = ""; if (str1 != null) { rVal += str1; } if (str2 != null) { rVal += str2; } } return rVal; } Here are some of the requirements: If both str1 and str2 are null, the method returns null If either str1 or str2 is null, it will just return the not null String If str1 and str2 are not null, it will concatenate them It never adds "null" to the result Can anyone do this with less code?

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• Java ServerSocketChannel SocketChannel (Callback)

  - by ikurtz

  I am trying to learn Java. I would like to implement a simple networked connect 4 game as well as a chat feature. I want my network logic to be non blocking so after much study I found that SocketChannel is what I am after regrading my needs. What has not made sense still is the lack of CallBack functions in SocketChannels.. Like one finds in C#. My query for this time is: How do I deliver the data received to the Chat or Game form (JFrame)? Some guidance is most welcome.

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• Updating a database periodically with Java

  - by MSR

  I would like to perform updates to a MySQL database using two separate classes (that do different things) -- one doing so every 10 seconds, and the second every minute. I have a few gaps in my Java knowledge and I'm wondering what the best way to achieve it is. Importantly, if connectivity to the database is lost, I need reconnection attempts to occur indefinitely, and I'm guessing the use of Prepared Statements will make queries more efficient. Should the connection to the database be left open all the time or closed between the updates being run? Maybe I also need to think about clearing objects/resources out of memory if the class instances are going to be run indefinitely.

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• Deploy Java application on MacOSX (from a Windows system)

  - by Matías

  Hello, Here's the deal. I'm just starting with Java programming, I've made a simple application that uses SWT graphic library and I want to deploy it on a Mac (running the latest version of MacOS X). I did all the programming in my Windows 7 machine, so here are my questions: Q1) Can I make an executable file for MacOS X from my Windows machine? How? (I saw that it's possible to create .exe files on Windows, instead of using .jar; I want to do the same for the Mac, of course it won't be an .exe) Q2) If I export my project in Eclipse and I choose Runnable JAR File and then on Library Handling I pick Extract required libraries into generated JAR or Package required libraries into generated JAR I end up with a huge .JAR (about 15MB of size, my application consist in just a button on a Window and a tiny method that doesn't do much). Is that considered normal? Here's the list of libraries that my project appears to be using: Thanks in advance.

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• Thread Jobs in Java

  - by Bragaadeesh

  Hi, I want to spawn 200 threads simultaneously in Java. What I'm doing right now is running into a loop and creating 200 threads and starting them. After these 200 gets completed, I want to spawn another 200 set of threads and so on. The gist here is that the first 200 threads I spawned need to be FINISHED before spawning the next set. I tried the code below, but its not working for(int i=0;i<200;i++){ Thread myThread = new Thread(runnableInstance); myThread.start(); } for(int i=0;i<200;i++){ Thread myThread = new Thread(runnableInstance); myThread.start(); } Note: I have intentionally put the for loop Twice, but the desired effect I intend is not happening simply because the second for loop is executed before the first set of threads end their execution. Please advise

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• Java: ListA.addAll(ListB) fires NullPointerException?

  - by HH

  The err part is Capitalized in the code, it also comes in foreaching. Because of the abstract list, it cannot be initialized, declaration is in a static field. The lists have the same type. import java.util.*; public class Test { public static final List<String> highPrio = Arrays.asList("*","/"); public static List<String> ops; public static void main(String[] args) { //ERROR HERE, why do it throw nullPointer? ops.addAll(highPrio); for(String s : ops) { System.out.println(s); } } }

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• [java] How to get ALL the information from a socket

  - by raven

  Hello, I'll begin this question with the claim that I have read the java networking guide before asking you. I do not understand how to READ the socket and get all the info summed up into a string. the socket might contains more than 1 line [trying to make a chat]. Please do no refer me to any other site unless it clearly states "this exact line does this.." because I failed to understand what this code part does BufferedReader stdIn = new BufferedReader( new InputStreamReader(System.in)); String userInput; while ((userInput = stdIn.readLine()) != null) { out.println(userInput); System.out.println("echo: " + in.readLine()); } Please, I just want to make a loop that will receive information from a socket, get all the content together into one string [I also want it to know where to add another line]. Thanks allot for anyone who helps, I have been trying to get an answer from tuts for hours and just failed to understand!

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• Java: Get current Date and Time from Server not System clock

  - by Insectatorious

  In my Java program, I need to create an instance of the current moment in time. I use Date date = new Date(); This gives me the current date and time as per the host machine's system clock. Is there any way I can get the current date and time from an online server? The world time server perhaps? I have seen this post and it describes what I want but I'm afraid I need more help than what's provided there. In a nutshell, I want to get a date and time that is not dependant on the host machine's system clock. Thanks!

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