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• Java - Reg. Ex. File Question

  - by aloh

  I'm grabbing lines from a text file and sifting line by line using regular expressions. I'm trying to search for blank lines, meaning nothing or just whitespace. However, what exactly is empty space? I know that whitespace is \s but what is a line that is nothing at all? null (\0)? newline (\n)? I tried the test harness in the Java tutorial to try and test to see what an empty space is but no luck so far.

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• Java - jar with librairies included

  - by kozher

  I am currently trying to make a Jar with all my librairies included. What I have done. I have created folders like this : - main folder - class (which contain all my classes) - ressources (containing all my librairies : mongo, jedis...) - MANIFEST.MF My main class is named process. My manifest is like this : Main-Class: processEAN Class-Path: ressources\commons-pool-1.5.6.jar ressources\jedis-2.0.0.jar resources\mongo-2.6.3.jar class - I have generated the JAR with this command : jar cvmf MANIFEST.MF processEAN.jar class/*.class ressources/*.jar My problem : When executing the JAR I have still the message "Exception in thread "main" java.lang.NoClassDefFoundError: processEAN" Any ideas ? Thanks

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• INSERT SQL in Java

  - by Pierre

  Hello. I have a Java application and I want to use SQL database. I have a class for my connection : public class SQLConnection{ private static String url = "jdbc:postgresql://localhost:5432/table"; private static String user = "postgres"; private static String passwd = "toto"; private static Connection connect; public static Connection getInstance(){ if(connect == null){ try { connect = DriverManager.getConnection(url, user, passwd); } catch (SQLException e) { JOptionPane.showMessageDialog(null, e.getMessage(), "Connection Error", JOptionPane.ERROR_MESSAGE); } } return connect; } } And now, in another class I succeeded to print my values but when I attempt to insert a value nothing is happening ... Here's my code : try { Statement state = SQLConnection.getInstance().createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY); Statement state2 = SQLConnection.getInstance().createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE); state2.executeUpdate("INSERT INTO table(field1) VALUES (\"Value\")"); // Here's my problem ResultSet res = state.executeQuery("SELECT * FROM plateau");

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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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• Saving object state on Java without using external memory

  - by TryHarder

  Good day. I know that in order to save object state in Java I should use serialization. But in every single topic about serialization states that I must save my object somewhere (disk, network). My problem is that I'm not allowed to do so. I need a way to save and recover object state without writing it on "external" memory. Maybe to save it on heap or stack... Please don't offer to clone it, I'm not allowed to do so as well. Thanks.

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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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• C++ / Java: Toggle boolean statement?

  - by Martijn Courteaux

  Hi, Is there a short way to toggle a boolean? With integers we can do operations like this: int i = 4; i *= 4; // equals 16 /* Which is equivalent to */ i = i * 4; So is there also something for booleans (like the *= operator for ints)? In C++: bool booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something? In Java: boolean booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something?

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• How to load modules in Java

  - by gerardorn

  I'm building a server that loads modules. Each module is a .jar file. Inside the jar there's all the classes that the module needs. The server needs to read the jar, find the main class (it doesnt have the main method on it is just the class that makes the module work but not as a different program), build an object of that class and store it in a vector of modules so that it can acces to a specific module depending on the job to be done. How can I do that? As far as the server, it is listening and receiving request, but there's no modules to delegate the job to, since my vector of modules is empty.

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• are Hierarchical SIngletons in Java possible?

  - by Zach H

  I've been toying with an interesting idea (No idea if I'll include it in any code, but it's fun to think about) Let's say we have a program that requires a large number of classes, all of a certain subclass. And those classes all need to be singletons. Now, we could write the singleton pattern for each of those classes, but it seems wasteful to write the same code over and over, and we already have a common base class. It would be really nice to create a getSingleton method of A that when called from a subclass, returns a singleton of the B class (cast to class A for simplicity) class A{ public A getSingleton(){ //Wizardry } } class B extends A{ } A blargh = B.getSingleton() A gish = B.getSingleton() if(A == B) System.out.println("It works!") It seems to me that the way to do this would be to recognize and call B's default constructor (assuming we don't need to pass anything in.) I know a little of the black magic of reflection in Java, but i'm not sure if this can be done. Anyone interested in puzzling over this?

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• Duel Masters game in Java

  - by Arun Ramasubramanian

  I was trying to make a Duel Masters card game in Java using BlueJ, and came up with a lot of ideas. However, I could not exactly figure out how to sort a deck on basis of the card names in the game. I have an array of Card objects(each has, as its instance variables: String name, int cost, int civ), and I want to sort them based on name. ie: if I have the cards "Pyrofighter Magnus", "Bazagazeal Dragon" and another "Pyrofighter Magnus" in the array, the cards should be sorted on basis of their names. I know that I could use compareTo(), but is there an easier method? Anyone? Remember, the method that sorts the cards should be a modifier.

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• Java JFrame is very strange

  - by rodion

  When I am running this, JLabel is not visible, but when I resize window (with mouse) JLabel is showed. Why? import javax.swing.*; import java.awt.*; public class FrmTaoLogin extends JFrame { private JPanel pnlLeft = new JPanel(); public FrmTaoLogin() { super(); pnlLeft.setBorder(BorderFactory.createEtchedBorder()); pnlLeft.add(new JLabel("test1")); getContentPane().add(pnlLeft,BorderLayout.SOUTH); setDefaultCloseOperation(EXIT_ON_CLOSE); setSize(200, 200); } public static void main(String[] args) { FrmTaoLogin FrmLogin = new FrmTaoLogin(); FrmLogin.setVisible(true); } }

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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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• Adding Timestamp to Java's GC messages in Tomcat 6

  - by ripper234

  I turned on Java's GC log options -XX:+PrintGC -XX:+PrintGCTimeStamps -XX:+PrintGCDetails Which print out these messages to standard output (catalina.out): 314.884: [CMS-concurrent-mark-start] 315.014: [CMS-concurrent-mark: 0.129/0.129 secs] [Times: user=0.14 sys=0.00, real=0.13 secs] 315.014: [CMS-concurrent-preclean-start] 315.016: [CMS-concurrent-preclean: 0.003/0.003 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 315.016: [CMS-concurrent-abortable-preclean-start] 332.055: [GC 332.055: [ParNew: 17128K->84K(19136K), 0.0017700 secs] 88000K->70956K(522176K) icms_dc=4 , 0.0018660 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] CMS: abort preclean due to time 352.253: [CMS-concurrent-abortable-preclean: 0.023/37.237 secs] [Times: user=0.78 sys=0.02, real=37.23 secs] How can I make these log lines appear with an actual timestamp (including date) instead of these numbers, which presumably mean "time since JVM started" ?

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• Circle class in java

  - by user292395

  I need to get the Java code for the below problem asap. Create a class Circle that will allow us to define a circle with a specific radius. Your class should include the following methods: A constructor that can create a circle with a specified radius. A method setRadius that sets a specific value as a new radius for an existing circle. A method getRadius that returns the radius of an existing circle. A method toString that returns a String with all the information about an existing circle. A method computeArea that computes the area of a circle A method computePerimeter that computes the perimeter of a circle.

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• Simulating python's With statement in java

  - by drozzy

  Is there something like Python with context manager in Java? For example say I want to do something like the following: getItem(itemID){ Connection c = C.getConnection(); c.open(); try{ Item i = c.query(itemID); }catch(ALLBunchOfErrors){ c.close(); } c.close(); return c; } where in python I just have: with( C.getConnection().open() as c): Item i = c.query(itemID); return i;

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• Is this valid Java code?

  - by Eric

  I'm using Eclipse, and it is perfectly happy with the following code: public interface MessageType { public static final byte KICK = 0x01; public static final byte US_PING = 0x02; public static final byte GOAL_POS = 0x04; public static final byte SHUTDOWN = 0x08; public static final byte[] MESSAGES = new byte[] { KICK, US_PING, GOAL_POS, SHUTDOWN }; } public class MessageTest implements MessageType { public static void main(String[] args) { int b = MessageType.MESSAGES.length; //Not happy } } However, the platform that I'm running it on crashes at the line marked above. By crash, think an equivalent of a BSOD. Is there anything wrong with my code, or do I need to pursue the developers of the Java VM for my platform?

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• Cant communicate with server in java

  - by cerq

  i m trying to write server to client program but i cant communicate with server in java. Below there is code block in my main. InetAddress addr = InetAddress.getLocalHost(); ipAddress = "78.162.206.164"; ServerSocket serverSocket = new ServerSocket(0); String randomStringForPlayerName = RandomStringGenerator.generateRandomString(); baseForReqOpp += ipAddress + " " + serverSocket + " " + randomStringForPlayerName; Socket socket = new Socket(host,2050); socket.setSoTimeout(100); in = new BufferedReader(new InputStreamReader(socket.getInputStream())); out = new PrintWriter(socket.getOutputStream()); out.write(baseForReqOpp); out.flush(); System.out.println(in.read()); i know there is no problem in server code and all the ports in communication are ok. But i cant read anything from server. What can be the problem?

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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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• Java how to load modules

  - by gerardorn

  heres my problem: im building a server that loads modules. each module is a .jar file. inside the jar theres all the classes that the module need. the server needs to read the jar, find the main class (it doesnt have the main method on it is just the class that makes the module work but not as a different program), build an object of that class and store it in a vector of modules so that it can acces to a specific module depending on the job to be done. how can i do that? as far as the server, it is listening and reciving request, but thes no modules to delegate the job to, since my vector of modules is empty

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• removing the first value in an array c# or java

  - by MrCode

  hey there i was working on a program and was thinking is it possible was to remove the value from the first element in an array. Has anyone any ideas on how this could be done ? thanks for all input is much appreciated. i have only tried removing from the last element wasnt sure on how i would remove the first this is how i done the last element try { if (isEmpty()) { throw new Exception("list is empty"); } size = size -1; return values[size]; } catch(Exception e) { System.out.println(e); return -1; }

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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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• 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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• 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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• Java input Letter

  - by xyvyre

  I'm doing an java activity that if Name start with letter A-G and Ends with Letter H-z the output is invalid heres my code: System.out.print("Enter your name: "); String str = in.readLine(); if(str.startsWith("a" )){ System.out.print("INVALID!"); } if(str.endsWith("h")){ System.out.print("INVALID!"); } This works but how can i implement letter a to g and h to z i already try this [a-g] and it not WORK!

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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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