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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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• 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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• Java Inheritance Concept Understanding

  - by Nirmal

  Hello All.... I am just refreshing the oops features of the java. So, I have a little confusion regarding inheritance concept. For that I have a following sample code : class Super{ int index = 5; public void printVal(){ System.out.println("Super"); } } class Sub extends Super{ int index = 2; public void printVal(){ System.out.println("Sub"); } } public class Runner { public static void main(String args[]){ Super sup = new Sub(); System.out.println(sup.index+","); sup.printVal(); } } Now above code is giving me output as : 5,Sub. Here, we are overriding printVal() method, so that is understandable that it is accessing child class method only. But I could not understand why it's accessing the value of x from Super class... Thanks in advance....

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• Java Applet : Nested Loops color change

  - by Bader

  Hello I have like a table to make a nested loop in Java applet , during this loop i should change the colors like the picture said. now i successed to make the table but i cannot change the colors because every time i try a forumla , it doesn't work. Here is my code int x = 63; for (int r=1; r<=10;r++) { Color C = new Color(0,10 +(x * 2),0); for (int c=0; c<=4; c++) { Color C2 = new Color(10 + (x * 2) ,0,0); g.setColor(C2); Font F = new Font("Arial",Font.BOLD, 24); g.setFont(F); g.drawString("Hello",10 + ( c * 60), r * 25 ); } } what should i do to make it work ?

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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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• NoSuchMethodException while using JAVA Reflection

  - by Appps

  Hi I'm trying to use reflection to invoke a method and update the setter value of that method. But I'm getting NoSuchMethodException while ivoking that method. com.test.Test.setAddress1(java.lang.Double) .But I've this method defined in my Class. Is the problem with my code. Can someone please help me? Thanks in advance. I've my code below. Class[] doubleArrayParamTypes = new Class[ 1 ]; doubleArrayParamTypes[ 0 ] = Double.class; Class class=Class.forName( "com.test.Test"); Object voObject = class.newInstance(); String data="TestData"; performMapping(class,"setAddress1",doubleArrayParamTypes ,voObject,data); /* Reflection to set the data */ private void performMapping(Class class,String methodName,Class[] clazz,Object voObject,Object data) { class.getMethod( "set" + methodName, clazz ).invoke( voObject, data ); }

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• while loop / string input not working java

  - by Mikeecb

  I have looked online and all of the tutorials / questions have pointed me to this. I can't see why this isn't working. Any help would be much appreciated. Thanks import java.util.*; public class test { static Scanner userInput = new Scanner(System.in); public static void main(String[] args) { String textEntered = userInput.next(); if (textEntered == "hello") { System.out.println("Hello to you too!"); } } } I enter "hello" but nothing is printed. Also I have tried next() and nextLine();

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• Java Sql Udate error, data type missmatch

  - by codo

  I have created a table in ms access. I have set the data type of ID to Auto Number in MS-access. In java when I try to update a record. the netBeans IDE gives me the error of " data type missmatch in criteria expression". But when I changed the ID number that was not in the table already it works well. The code is below. String sql = "Update table1 set price ='" + txtPrice.getText() + "', quantity='" + txtQuantity.getText() + "', description='" + txtDescription.getText() + "' where id= " + txtid.getText() + ""; try { pst = conn.prepareStatement(sql); pst.executeUpdate(); JOptionPane.showMessageDialog(null, "Updated"); UpdateJTable(); } catch (Exception e) { JOptionPane.showMessageDialog(null, e); }

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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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• 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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• How to avoid recursion in Java SecurityManager checkConnect?

  - by Zilupe

  I'm trying to take control of a Java code base that does lots of un-documented things. I'm using a custom SecurityManager to check permission requests. Specifically, my code is checking SocketPermission checks -- checkConnect. checkConnect is called when the application tries to resolve a host name to IP address and to connect to a specific IP address. The problem is that I don't know how to properly call host name resolution (InetAddress.getAddressByName) without falling into infinite recursion, because normally checkConnect is called even when I resolve the name from inside the SecurityManager.checkConnect. I have read on the web that I have to call the address resolution from a doPrivileged block, but no idea how. P.S. Is this possible without writing any policy files?

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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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• Authenticating a SOAP service in Java (password security)

  - by user1686448

  I am writing an application, in Java, which needs to log in to a remote SOAP service (JIRA) prior to calling methods on that service. I have looked at examples of how to do this, for example http://www.j-tricks.com/1/post/2010/8/jira-soap-client.html, however I am concerned that I need to put the password in memory at some point. I've read that I should store the password as a char[] but still, I'm concerned about storing the password in the clear at all. How should I store the password used by my client to log into the SOAP service? And how should I read it and pass it to JIRA?

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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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• How do I calculate someone's age in Java?

  - by nojevive

  I want to return an age in years as an int in a Java method. What I have now is the following where getBirthDate() returns a Date object (with the birth date ;-)): public int getAge() { long ageInMillis = new Date().getTime() - getBirthDate().getTime(); Date age = new Date(ageInMillis); return age.getYear(); } But since getYear() is deprecated I'm wondering if there is a better way to do this? I'm not even sure this works correctly, since I have no unit tests in place (yet).

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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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• 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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• Java - Optimize finding a string in a list

  - by Mark

  I have an ArrayList of objects where each object contains a string 'word' and a date. I need to check to see if the date has passed for a list of 500 words. The ArrayList could contain up to a million words and dates. The dates I store as integers, so the problem I have is attempting to find the word I am looking for in the ArrayList. Is there a way to make this faster? In python I have a dict and mWords['foo'] is a simple lookup without looping through the whole 1 million items in the mWords array. Is there something like this in java? for (int i = 0; i < mWords.size(); i++) { if ( word == mWords.get(i).word ) { mLastFindIndex = i; return mWords.get(i); } }

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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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• 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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• 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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• [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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• How to implement low pass filter using java

  - by chai

  Hello Everyone, I am trying to implement a low pass filter in Java. My requirement is very simple,I have to eliminate signals beyond a particular frequency (Single dimension). Looks like Butterworth filter would suit my need. Now the important thing is that CPU time should be as low as possible. There would be close to a million sample the filter would have to process and our users don't like waiting too long. Are there any readymade implementation of Butterworth filters which has optimal algorithms for filtering. Regards, Chaitannya

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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: 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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