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  • java.lang.ClassNotFoundException in Netbeans. 5 hours to fix

    - by user1304281
    Hi I've got to submit an interpreter assignment tonight and all of a sudden it stopped working! It was working yesterday but now when I try to create a class instance at runtime I get classnotfoundexception. My project has no libraries or dependencies, I've written everything myself. I've googled around and it seems to be an issue with classpath but I've had no luck fooling with the project properties on netbeans. Here's some code: package interpreter; import interpreter.bytecode.ByteCode; import java.io.*; import java.lang.reflect.*; class ByteCodeLoader { //.... String codeClass = CodeTable.CodeTable.get(args[0]); ByteCode bytecode = (ByteCode)(Class.forName("interpreter.bytecode."+codeClass).newInstance()); //this throws exception } all of my ByteCodes are contained within a subpackage of interpreter called interpreter.bytecode. I'll be watching this thread so I can answer/clarify any questions immediately. Thanks for your time!

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  • Velocity engine fails to load template from a remote shared folder

    - by performanceuser
    I have following code File temlateFile = new File( "D:/config/emails/MailBody.vm" ); temlateFile.exists(); VelocityEngine velocityEngine = new VelocityEngine(); velocityEngine.setProperty(RuntimeConstants.RESOURCE_LOADER, "file"); velocityEngine.setProperty("file.resource.loader.class", FileResourceLoader.class.getName()); velocityEngine.setProperty("file.resource.loader.path", temlateFile.getParentFile().getAbsolutePath()); velocityEngine.init(); template = velocityEngine.getTemplate( temlateFile.getName() ); This works because it is loading a file from local file system. Once I change the first like to: File temlateFile = new File( "//remote/config/emails/MailBody.vm" ); It doesn't work. org.apache.velocity.exception.ResourceNotFoundException: Unable to find resource 'MailBody.vm' at org.apache.velocity.runtime.resource.ResourceManagerImpl.loadResource(ResourceManagerImpl.java:474) at org.apache.velocity.runtime.resource.ResourceManagerImpl.getResource(ResourceManagerImpl.java:352) at org.apache.velocity.runtime.RuntimeInstance.getTemplate(RuntimeInstance.java:1533) at org.apache.velocity.runtime.RuntimeInstance.getTemplate(RuntimeInstance.java:1514) at org.apache.velocity.app.VelocityEngine.getTemplate(VelocityEngine.java:373) at com.actuate.iserver.mail.VelocityContent.<init>(VelocityContent.java:33) at com.actuate.iserver.mail.VolumeCreationMail.<init>(VolumeCreationMail.java:40) at com.actuate.iserver.mail.VolumeCreationMail.main(VolumeCreationMail.java:67) In both cases temlateFile.exists() always return true. Any ideas?

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  • Can JMX operations take interfaces as parameters?

    - by Thor84no
    I'm having problems with an MBean that takes a Map<String, Object> as a parameter. If I try to execute it via JMX using a proxy object, I get an Exception: Caused by: javax.management.ReflectionException at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:231) at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:668) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) Caused by: java.lang.IllegalArgumentException: Unable to find operation updateProperties(java.util.HashMap) It appears that it attempts to use the actual implementation class rather than the interface, and doesn't check if this is a child of the required interface. The same thing happens for extended classes (for example declare HashMap, pass in LinkedHashMap). Does this mean it's impossible to use an interface for such methods? At the moment I'm getting around it by changing the method signature to accept a HashMap, but it seems odd that I wouldn't be able to use interfaces (or extended classes) in my MBeans. Edit: The proxy object is being created by an in-house utility class called JmxInvocationHandler. The (hopefully) relevant parts of it are as follows: public class JmxInvocationHandler implements InvocationHandler { ... public static <T> T createMBean(final Class<T> iface, SFSTestProperties properties, String mbean, int shHostID) { T newProxyInstance = (T) Proxy.newProxyInstance(iface.getClassLoader(), new Class[] { iface }, (InvocationHandler) new JmxInvocationHandler(properties, mbean, shHostID)); return newProxyInstance; } ... private JmxInvocationHandler(SFSTestProperties properties, String mbean, int shHostID) { this.mbeanName = mbean + MBEAN_SUFFIX + shHostID; msConfig = new MsConfiguration(properties.getHost(0), properties.getMSAdminPort(), properties.getMSUser(), properties.getMSPassword()); } ... public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (management == null) { management = ManagementClientStore.getInstance().getManagementClient(msConfig.getHost(), msConfig.getAdminPort(), msConfig.getUser(), msConfig.getPassword(), false); } final Object result = management.methodCall(mbeanName, method.getName(), args == null? new Object[] {} : args); return result; } }

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  • Iterating over member typed collection fails when using untyped reference to generic object

    - by Alexander Pavlov
    Could someone clarify why iterate1() is not accepted by compiler (Java 1.6)? I do not see why iterate2() and iterate3() are much better. This paragraph is added to avoid silly "Your post does not have much context to explain the code sections; please explain your scenario more clearly." protection. import java.util.Collection; import java.util.HashSet; public class Test<T> { public Collection<String> getCollection() { return new HashSet<String>(); } public void iterate1(Test test) { for (String s : test.getCollection()) { // ... } } public void iterate2(Test test) { Collection<String> c = test.getCollection(); for (String s : c) { // ... } } public void iterate3(Test<?> test) { for (String s : test.getCollection()) { // ... } } } Compiler output: $ javac Test.java Test.java:11: incompatible types found : java.lang.Object required: java.lang.String for (String s : test.getCollection()) { ^ Note: Test.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 1 error

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  • java.net.BindException How can I clear the sockets or what ever is causing it?

    - by user2266067
    I need some help with, I guess a simple networking related problem I'm having. It will also help me better understand how all this works by knowing what isn't being .close()'ed. I'm sure this is pretty simple, but for me its all very new. This is the client program. I can most likely append the server then, if I can figure this out. Thanks public class Server { public static void main(String[] args) { start(); } static int start = 0; public static void start() { try { ServerSocket serverSocket = new ServerSocket(4567); Socket socket = serverSocket.accept(); //1) Take and echo input (In this case a message) BufferedReader bf = new BufferedReader(new InputStreamReader(socket.getInputStream())); String message = bf.readLine(); System.out.println("Message recieved from Client:" + message); //2) Response of client message PrintWriter printWriter = new PrintWriter(socket.getOutputStream(), true); printWriter.println("Server echoing back the message ' " + message + " ' from Client"); } catch (IOException e) { System.out.println("e " + e); System.exit(-1); } start++; clearUp(); if (start < 5) { System.out.println("Closing binds and Restarting" + start); start(); } } public void clearUp(){ //How would I clear the stuff that is left bound so I can restart via start() and avoid the java.net.BindException: Address already in use: JVM_Bind ? } } How would I clear the stuff that is left bound so I can restart via start() and avoid java.net.BindException: Address already in use: JVM_Bind ?

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  • em.createQuery keeps returning null

    - by Developer106
    I have this application which i use JSF 2.0 and EclipseLink, i have entities created for a database made in MySQL, Created these entities using netbeans 7.1.2, it gets created automaticly. Then i use session beans to work with these entities, the thing is the em.createQuery always returns a null, though I checked NamedQueries in the entities and they perfectly match a sample from the entities named queries:- @NamedQueries({ @NamedQuery(name = "Users.findAll", query = "SELECT u FROM Users u"), @NamedQuery(name = "Users.findByUserId", query = "SELECT u FROM Users u WHERE u.userId = :userId"), @NamedQuery(name = "Users.findByUsername", query = "SELECT u FROM Users u WHERE u.username = :username"), @NamedQuery(name = "Users.findByEmail", query = "SELECT u FROM Users u WHERE u.email = :email"), notice how i use this findByEmail query in the session bean :- public Users findByEmail(String email){ em.getTransaction().begin(); String find = "Users.findByEmail"; Query query = em.createNamedQuery(find); query.setParameter("email", email); Users user = (Users) query.getSingleResult(); but it always returns null from this em.createNamedQuery, i tried using .createQuery first but it also was no good. the stacktrace of the exception Caused by: java.lang.NullPointerException at com.readme.entities.sessionBeans.UsersFacade.findByEmail(UsersFacade.java:48) at com.readme.user.signup.SignupBean.checkAvailability(SignupBean.java:137) at com.readme.user.signup.SignupBean.save(SignupBean.java:146) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) What Seems To Be The Problem Here ?

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  • Recursive breadth-first travel function in Java or C++?

    - by joejax
    Here is a java code for breadth-first travel: void breadthFirstNonRecursive(){ Queue<Node> queue = new java.util.LinkedList<Node>(); queue.offer(root); while(!queue.isEmpty()){ Node node = queue.poll(); visit(node); if (node.left != null) queue.offer(node.left); if (node.right != null) queue.offer(node.right); } } Is it possible to write a recursive function to do the same? At first, I thought this would be easy, so I came out with this: void breadthFirstRecursive(){ Queue<Node> q = new LinkedList<Node>(); breadthFirst(root, q); } void breadthFirst(Node node, Queue<Node> q){ if (node == null) return; q.offer(node); Node n = q.poll(); visit(n); if (n.left != null) breadthFirst(n.left, q); if (n.right != null) breadthFirst(n.right, q); } Then I found it doesn't work. It is actually does the same thing as this: void preOrder(Node node) { if (node == null) return; visit(node); preOrder(node.left); preOrder(node.right); } Has any one thought about this before?

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  • Why do you have to call URLConnection#getInputStream to be able to write out to URLConnection#getOutputStream?

    - by John
    I'm trying to write out to URLConnection#getOutputStream, however, no data is actually sent until I call URLConnection#getInputStream. Even if I set URLConnnection#doInput to false, it still will not send. Does anyone know why this is? There's nothing in the API documentation that describes this. Java API Documentation on URLConnection: http://download.oracle.com/javase/6/docs/api/java/net/URLConnection.html Java's Tutorial on Reading from and Writing to a URLConnection: http://download.oracle.com/javase/tutorial/networking/urls/readingWriting.html import java.io.IOException; import java.io.OutputStreamWriter; import java.net.URL; import java.net.URLConnection; public class UrlConnectionTest { private static final String TEST_URL = "http://localhost:3000/test/hitme"; public static void main(String[] args) throws IOException { URLConnection urlCon = null; URL url = null; OutputStreamWriter osw = null; try { url = new URL(TEST_URL); urlCon = url.openConnection(); urlCon.setDoOutput(true); urlCon.setRequestProperty("Content-Type", "text/plain"); //////////////////////////////////////// // SETTING THIS TO FALSE DOES NOTHING // //////////////////////////////////////// // urlCon.setDoInput(false); osw = new OutputStreamWriter(urlCon.getOutputStream()); osw.write("HELLO WORLD"); osw.flush(); ///////////////////////////////////////////////// // MUST CALL THIS OTHERWISE WILL NOT WRITE OUT // ///////////////////////////////////////////////// urlCon.getInputStream(); ///////////////////////////////////////////////////////////////////////////////////////////////////////// // If getInputStream is called while doInput=false, the following exception is thrown: // // java.net.ProtocolException: Cannot read from URLConnection if doInput=false (call setDoInput(true)) // ///////////////////////////////////////////////////////////////////////////////////////////////////////// } catch (Exception e) { e.printStackTrace(); } finally { if (osw != null) { osw.close(); } } } }

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  • What is the error in this java code ? What changes should I do to remove it ?

    - by mekasperasky
    import javax.swing.*; // For JPanel, etc. import java.awt.*; // For Graphics, etc. import java.awt.geom.*; // For Ellipse2D, etc. public class ShapeExample extends JPanel { private Ellipse2D.Double circle = new Ellipse2D.Double(10, 10, 350, 350); private Rectangle2D.Double square = new Rectangle2D.Double(10, 10, 350, 350); public void paintComponent(Graphics g) { clear(g); Graphics2D g2d = (Graphics2D)g; g2d.fill(circle); g2d.draw(square); } // super.paintComponent clears offscreen pixmap, // since we're using double buffering by default. protected void clear(Graphics g) { super.paintComponent(g); } protected Ellipse2D.Double getCircle() { return(circle); } public static void main(String[] args) { WindowUtilities.openInJFrame(new ShapeExample(), 100, 100); } } The error I am getting is this . symbol : variable WindowUtilities location: class ShapeExample WindowUtilities.openInJFrame(new ShapeExample(), 100, 100); ^ 1 error What is wrong in the code? r

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  • Intelligent search and generation of Java code, preferrably using Python?

    - by Ipsquiggle
    Basically, I do lots of one-off code generation, large-scale refactorings, etc. etc. in Java. My tool language of choice is Python, but I'll take whatever solutions you can offer. Here is a simplified illustration of what I would like, in a pseudocode Generating an implementation for an interface search within my project: for each Interface as iName: write class(name=iName+"Impl", implements=iName) search within the body of iName: for each Method as mName: write method(name=mName, body="// TODO implement this...") Basically, the tool I'm searching for would allow me to: parse files according to their Java structure ("search for interfaces") search for words contextualized by language elements and types ("variables of type SomeClass", "doStuff() method calls on SomeClass instances") to run searches with structural context ("within the body of the current result") easily replace or generate code (with helpers to generate, as above, or functions for replacing, "rename the interface to Foo", "insert the line Blah.Blah()", etc.) The point is, I don't want to spend a lot of time writing these things, as they are usually throwaway. But sometimes I need something just a little smarter than what grep offers. It wouldn't be too hard to write up a simplistic version of this, but if I'm going to use something like this at all, I'd expect it to be robust. Any suggestions of a tool/library that will help me accomplish this?

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  • MidiSystem.getSequencer() returns Audio Device Unavailable

    - by ksemeks
    I've keep having an exception thrown, on and on. When i try to make a new Sequencer object, i keep getting the javax.sound.midi.MidiUnavailableException: Audio Device Unavailable exception. So, here's the code: import javax.sound.midi.*; public class MiniMusicPlayer1 { public static void main(String[] args) { try { Sequencer sequencer = MidiSystem.getSequencer(); sequencer.open(); Sequence seq = new Sequence(Sequence.PPQ, 4); Track track = seq.createTrack(); for (int i = 5; i < 61; i += 4) { track.add(makeEvent(144, 1, i, 100, i)); track.add(makeEvent(128, 1, i, 100, (i+2))); } sequencer.setSequence(seq); sequencer.setTempoInBPM(220); sequencer.start(); } catch (Exception e) { e.printStackTrace(); } } public static MidiEvent makeEvent(int comd, int chan, int one, int two, int tick) { MidiEvent event = null; try { ShortMessage a = new ShortMessage(); a.setMessage(comd, chan, one, two); event = new MidiEvent(a, tick); } catch (Exception e) { e.printStackTrace(); } return event; } } And here's the complete error (at compile): javax.sound.midi.MidiUnavailableException: Audio Device Unavailable at com.sun.media.sound.MixerSynth.implOpen(MixerSynth.java:165) at com.sun.media.sound.AbstractMidiDevice.doOpen(AbstractMidiDevice.java:144) at com.sun.media.sound.AbstractMidiDevice.openInternal(AbstractMidiDevice.java:134) at com.sun.media.sound.AbstractMidiDevice.getReceiverReferenceCounting(AbstractMidiDevice.java:339) at javax.sound.midi.MidiSystem.getReceiver(MidiSystem.java:243) at javax.sound.midi.MidiSystem.getSequencer(MidiSystem.java:442) at javax.sound.midi.MidiSystem.getSequencer(MidiSystem.java:348) at MiniMusicPlayer1.main(MiniMusicPlayer1.java:9) First i was unable to play MIDI files on my pc, but then i got it to work, so now i can play MIDI files, that's okay. I tried even to close every process which uses my sound card, but the error is still there. Anyone can help me?

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  • Does the Java Memory Model (JSR-133) imply that entering a monitor flushes the CPU data cache(s)?

    - by Durandal
    There is something that bugs me with the Java memory model (if i even understand everything correctly). If there are two threads A and B, there are no guarantees that B will ever see a value written by A, unless both A and B synchronize on the same monitor. For any system architecture that guarantees cache coherency between threads, there is no problem. But if the architecture does not support cache coherency in hardware, this essentially means that whenever a thread enters a monitor, all memory changes made before must be commited to main memory, and the cache must be invalidated. And it needs to be the entire data cache, not just a few lines, since the monitor has no information which variables in memory it guards. But that would surely impact performance of any application that needs to synchronize frequently (especially things like job queues with short running jobs). So can Java work reasonably well on architectures without hardware cache-coherency? If not, why doesn't the memory model make stronger guarantees about visibility? Wouldn't it be more efficient if the language would require information what is guarded by a monitor? As i see it the memory model gives us the worst of both worlds, the absolute need to synchronize, even if cache coherency is guaranteed in hardware, and on the other hand bad performance on incoherent architectures (full cache flushes). So shouldn't it be more strict (require information what is guarded by a monitor) or more lose and restrict potential platforms to cache-coherent architectures? As it is now, it doesn't make too much sense to me. Can somebody clear up why this specific memory model was choosen? EDIT: My use of strict and lose was a bad choice in retrospect. I used "strict" for the case where less guarantees are made and "lose" for the opposite. To avoid confusion, its probably better to speak in terms of stronger or weaker guarantees.

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  • Is there a nice way of having static generic parameters is Java?

    - by Chris
    Hello, recently I'm writing some functions that I take from Haskell and translate into Java. One of the main problems I have is I cannot easily create a static property with a generic type. Let me explain by a little example... // An interface to implement functions public interface Func<P, R> { public R apply(P p); } // What I want to do... (incorrect in Java) public class ... { public static <T> Func<T, T> identity = new Func<T, T>() { public T apply(T p) { return p; } } } // What I do right now public class ... { private static Func<Object, Object> identity = new Func<Object, Object>() { public Object apply(Object p) { return p; } } @SuppressWarnings("unchecked") public static <T> Func<T, T> getIdentity() { return (Func<T, T>)identity; } } Are there any easier ways to do something like that? What kind of problems might arise if the syntax I used would be valid?

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  • declare decision structure inside of a System.out.println

    - by user2899249
    So I am working on an assignment where I have to have a print method in a constructor that displays a distance. I also have to have three separate get methods depending on what the input is in the demo class. My question is that I am trying to write the print method to contain a decision structure based on which get is used. public void prt() { DecimalFormat formatter = new DecimalFormat("#,##0.00"); System.out.println("The time it takes the sound to travel " + distance + " feet through air is " + if (getSpeedInAir() > 0) { formatter.format(getSpeedInAir()); } else if (getSpeedInWater() > 0) { formatter.format(getSpeedInWater()); } else if (getSpeedInSteel() > 0) { formatter.format(getSpeedInSteel()); } else "error";) } After trying to compile I am getting the following errors. Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. All rights reserved. C:\Users\GlaDOS\Desktop\JavaStuffj Speed C:\Users\GlaDOS\Desktop\JavaStuffdel *.class C:\Users\GlaDOS\Desktop\JavaStuffjavac Speed.java Speed.java:43: error: illegal start of expression " feet through air is " + if (getSpeedInAir() 0) ^ Speed.java:43: error: ';' expected " feet through air is " + if (getSpeedInAir() 0) ^ Speed.java:43: error: not a statement " feet through air is " + if (getSpeedInAir() 0) ^ Speed.java:43: error: ';' expected " feet through air is " + if (getSpeedInAir() 0) ^ Speed.java:47: error: 'else' without 'if' else if (getSpeedInWater() > 0) ^ Speed.java:56: error: not a statement "error";) ^ Speed.java:56: error: illegal start of expression "error";) ^ 7 errors C:\Users\GlaDOS\Desktop\JavaStuffjava Speed Error: Could not find or load main class Speed Any help on why this is happening would be greatly appreciated.

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  • Can a Java HashMap's size() be out of sync with its actual entries' size ?

    - by trix
    I have a Java HashMap called statusCountMap. Calling size() results in 30. But if I count the entries manually, it's 31 This is in one of my TestNG unit tests. These results below are from Eclipse's Display window (type code - highlight - hit Display Result of Evaluating Selected Text). statusCountMap.size() (int) 30 statusCountMap.keySet().size() (int) 30 statusCountMap.values().size() (int) 30 statusCountMap (java.util.HashMap) {40534-INACTIVE=2, 40526-INACTIVE=1, 40528-INACTIVE=1, 40492-INACTIVE=3, 40492-TOTAL=4, 40513-TOTAL=6, 40532-DRAFT=4, 40524-TOTAL=7, 40526-DRAFT=2, 40528-ACTIVE=1, 40524-DRAFT=2, 40515-ACTIVE=1, 40513-DRAFT=4, 40534-DRAFT=1, 40514-TOTAL=3, 40529-DRAFT=4, 40515-TOTAL=3, 40492-ACTIVE=1, 40528-TOTAL=4, 40514-DRAFT=2, 40526-TOTAL=3, 40524-INACTIVE=2, 40515-DRAFT=2, 40514-ACTIVE=1, 40534-TOTAL=3, 40513-ACTIVE=2, 40528-DRAFT=2, 40532-TOTAL=4, 40524-ACTIVE=3, 40529-ACTIVE=1, 40529-TOTAL=5} statusCountMap.entrySet().size() (int) 30 What gives ? Anyone has experienced this ? I'm pretty sure statusCountMap is not being modified at this point. There are 2 methods (lets call them methodA and methodB) that modify statusCountMap concurrently, by repeatedly calling incrementCountInMap. private void incrementCountInMap(Map map, Long id, String qualifier) { String key = id + "-" + qualifier; if (map.get(key) == null) { map.put(key, 0); } synchronized (map) { map.put(key, map.get(key).intValue() + 1); } } methodD is where I'm getting the issue. methodD has a TestNG @dependsOnMethods = { "methodA", "methodB" } so when methodD is executing, statusCountMap is pretty much static already. I'm mentioning this because it might be a bug in TestNG. I'm using Sun JDK 1.6.0_24. TestNG is testng-5.9-jdk15.jar Hmmm ... after rereading my post, could it be because of concurrent execution of outside-of-synchronized-block map.get(key) == null & map.put(key,0) that's causing this issue ?

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  • how to transfer a time which was zero at year of 0000(maybe) to java.util.Date

    - by hguser
    I have a gps time in the database,and when I do some query,I have to use the java.util.Date,however I found that I do not know how to change the gps time to java.util.Date. Here is a example: The readable time === The GPS time 2010-11-15 13:10:00 === 634254192000000000 2010-11-15 14:10:00 === 634254228000000000 The period of the two date is "36000000000",,obviously it stands for one hour,so I think the unit of the gps time in the db must be nanosecond. 1 hour =3600 seconds= 3600*1000 milliseconds == 3600*1000*10000 nanoseconds Then I try to convert the gps time: Take the " 634254228000000000" as example,it stands for("2010-11-15 14:10:00"); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ssZ"); Date d = new Date(63425422800000L); System.out.println(sdf.format(d)); The result is 3979-11-15 13:00:00+0000. Of course it is wrong,then I try to calculate : 63425422800000/3600000/24/365=2011.xxx So it seems that the gps time here is not calcuated from Epoch(1970-01-01 00:00:00+0000). It maybe something like (0001-01-01 00:00:00+0000). Then I try to use the following method: Date date_0=sdf.parse("0001-01-01 00:00:00+0000"); Date d = new Date(63425422800000L); System.out.println(sdf.format(d.getTime() + date_0.getTime())); The result is: 2010-11-13 13:00:00+0000. :( Now I am confusing about how to calculate this gps time. Any suggestion?

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  • implementing interface

    - by 1ace1
    hello guys so i have this assignment that i need to implement interface to go over an ArrayList and sort it (ascending or descnding).I dont want "the" answer i just need some suggestions on my approach and why i get this error Exception in thread "main" java.lang.ClassCastException: Week7.Check cannot be cast to java.lang.Comparable at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at java.util.Collections.sort(Unknown Source) at Week7.TestCheck.main(TestCheck.java:18) This is how i did it: comparable had one method called public int compairTo(Object o) public class Check implements comparable { private Integer checkNumber; public Check(Integer newCheckNumber) { setCheckNumber(newCheckNumber); } public String toString() { return getCheckNumber().toString(); } public void setCheckNumber(Integer checkNumber) { this.checkNumber = checkNumber; } public Integer getCheckNumber() { return checkNumber; } @Override public int compairTo(Object o) { Check compair = (Check)o; int result = 0; if (this.getCheckNumber() > compair.getCheckNumber()) result = 1; else if(this.getCheckNumber() < compair.getCheckNumber()) result = -1; return result; } } in my main i had this import java.util.ArrayList; import java.util.Collections; public class TestCheck { public static void main(String[] args) { ArrayList checkList = new ArrayList(); checkList.add(new Check(445)); checkList.add(new Check(101)); checkList.add(new Check(110)); checkList.add(new Check(553)); checkList.add(new Check(123)); Collections.sort(checkList); for (int i =0; i < checkList.size(); i++){ System.out.println(checkList.get(i)); } } }

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  • question about Ackermann function

    - by davit-datuashvili
    i am doing to write recursive program which calculates Ackemann function http://en.wikipedia.org/wiki/Ackermann_function here is code public class Ackermann{ public static long ackermann( long m,long n){ return (m==0)? n+1: (m>0 && n==0)? ackermann(m-1,1): (m>0 && n>0)? ackermann(m-1, ackermann(m,n-1)); } public static void main(String[]args){ long m=4; long n=2; System.out.println(ackermann(m,n)); } } but it shows me mistakes Ackermann.java:7: : expected (m>0 && n>0)? ackermann(m-1, ackermann(m,n-1)); ^ Ackermann.java:7: ';' expected (m>0 && n>0)? ackermann(m-1, ackermann(m,n-1)); ^ Ackermann.java:18: illegal start of expression public static void main(String[]args){ ^ Ackermann.java:18: ';' expected public static void main(String[]args){ ^ Ackermann.java:18: illegal start of expression public static void main(String[]args){ ^ Ackermann.java:18: ';' expected public static void main(String[]args){ ^ Ackermann.java:18: ';' expected public static void main(String[]args){ ^ Ackermann.java:26: reached end of file while parsing } ^ 8 errors please help

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  • (Java) Get value of string loaded into dynamic-type object?

    - by Michael
    I'm very new to Java (~10 days), so my code is probably pretty bad, but here's what I've got: ArgsDataHolder argsData = new ArgsDataHolder(); // a class that holds two // ArrayList's where each element // representing key/value args Class thisArgClass; String thisArgString; Object thisArg; for(int i=2; i< argsString.length; i++) { thisToken = argsString[i]; thisArgClassString = getClassStringFromToken(thisToken).toLowerCase(); System.out.println("thisArgClassString: " + thisArgClassString); thisArgClass = getClassFromClassString(thisArgClassString); // find closing tag; concatenate middle Integer j = new Integer(i+1); thisArgString = getArgValue(argsString, j, "</" + thisArgClassString + ">"); thisArg = thisArgClass.newInstance(); thisArg = thisArgClass.valueOf(thisArgString); argsData.append(thisArg, thisArgClass); } The user basically has to input a set of key/value arguments into the command prompt in this format: <class>value</class>, e.g. <int>62</int>. Using this example, thisArgClass would be equal to Integer.class, thisArgString would be a string that read "62", and thisArg would be an instance of Integer that is equal to 62. I tried thisArg.valueOf(thisArgString), but I guess valueOf(<String>) is only a method of certain subclasses of Object. For whatever reason, I can't seem to be able to cast thisArg to thisArgClass (like so: thisArg = (thisArgClass)thisArgClass.newInstance();, at which point valueOf(<String>) should become accessible. There's got to be a nice, clean way of doing this, but it is beyond my abilities at this point. How can I get the value of the string loaded into a dynamically-typed object (Integer, Long, Float, Double, String, Character, Boolean, etc.)? Or am I just overthinking this, and Java will do the conversion for me? :confused:

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  • byte and short data types in Java can accept the value outside the range by explicit cast. The higher data types however can not. Why?

    - by Lion
    Let's consider the following expressions in Java. byte a = 32; byte b = (byte) 250; int i = a + b; This is valid in Java even though the expression byte b = (byte) 250; is forced to assign the value 250 to b which is outside the range of the type byte. Therefore, b is assigned -6 and consequently i is assigned the value 26 through the statement int i = a + b;. The same thing is possible with short as follows. short s1=(short) 567889999; Although the specified value is outside the range of short, this statement is legal. The same thing is however wrong with higher data types such int, double, folat etc and hence, the following case is invalid and causes a compile-time error. int z=2147483648; This is illegal, since the range of int in Java is from -2,147,483,648 to 2147483647 which the above statement exceeds and issues a compile-time error. Why is such not wrong with byte and short data types in Java?

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  • How to account for non-prime numbers 0 and 1 in java?

    - by shady
    I'm not sure if this is the right place to be asking this, but I've been searching for a solution for this on my own for quite some time, so hopefully I've come to the right place. When calculating prime numbers, the starting number that each number has to be divisible by is 2 to be a non-prime number. In my java program, I want to include all the non-prime numbers in the range from 0 to a certain number, so how do I include 0 and 1? Should I just have separate if and else-if statements for 0 and 1 that state that they are not prime numbers? I think that maybe 0 and 1 should be included in the java for loop, but I don't know how to go about doing that. for (int i = 2; i < num; i++){ if (num % i == 0){ System.out.println(i + " is not a prime number. "); } else{ System.out.println(i + " is a prime number. "); } }

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  • How to get java singleton object manager to return any type of object?

    - by Robert
    I'm writing an interactive fiction game in java from scratch. I'm currently storing all of my game object references in a hashmap in a singleton called ObjectManager. ObjectManager has a function called get which takes an integer ID and returns the appropriate reference. The problem is that it returns a BaseObject when I need to return subclasses of BaseObject with more functionality. So, what I've done so far is I've added a getEntity function which returns BaseEntity (which is a subclass of BaseObject). However, when I need the function to return to an object that is a subclass of BaseEntity that has added, required functionality, I will need to make another function. I know there is a better way, but I don't know what it is. I know very little of design patterns, and I'm not sure which one to use here. I tried passing 'class' as a parameter, but that didn't get me anywhere. public BaseObject get(int ID){ return (BaseObject)refMap.get(ID); } public BaseEntity getEntity(int ID){ return (BaseEntity)refMap.get(ID); } Thanks, java ninjas!

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  • Inheritance not working

    - by Pendo826
    Hey im just practicing inheritance and i encountered a problem. Im getting an error in my car class(sub-class) that the variables in Vehicle(parent) are not visible. i didnt do anything to change this and i dont even know how to make it invisible. Can anyone help me with this. public class Vehicle { private String make, model, colour; private int registrationNumber; public Vehicle() { this.make = ""; this.model = ""; this.colour = ""; this.registrationNumber = 0; } public Vehicle(String make, String model, String colour, int registrationNumber) { this.make = make; this.model = model; this.colour = colour; this.registrationNumber = registrationNumber; } public String getMake() { return make; } public void setMake(String make) { this.make = make; } public String getModel() { return model; } public void setModel(String model) { this.model = model; } public String getColour() { return colour; } public void setColour(String colour) { this.colour = colour; } public int getRegistrationNumber() { return registrationNumber; } public void setRegistrationNumber(int registrationNumber) { this.registrationNumber = registrationNumber; } public String toString() { return "Vehicle [make=" + make + ", model=" + model + ", colour=" + colour + ", registrationNumber=" + registrationNumber + "]"; } } public Car() { super(); this.doors = 0; this.shape = ""; } public Car(int doors, String shape, String make, String model, String colour, int registrationNumber) { super(); this.doors = doors; this.shape = shape; this.make = make;//Error this.model = model;//Error this.colour = colour;//Error this.registrationNumber = registrationNumber;//Error } The error message: Description Resource Path Location Type The field Vehicle.make is not visible Car.java /VehicleApp/src line 19 Java Problem The field Vehicle.model is not visible Car.java /VehicleApp/src line 20 Java Problem The field Vehicle.colour is not visible Car.java /VehicleApp/src line 21 Java Problem The field Vehicle.registrationNumber is not visible Car.java /VehicleApp/src line 22 Java Problem

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  • How to check whether a default browser is opened in the operating system (Java)?

    - by stempel1984
    Hi, I am newbie here. During my work, I faced an interesting problem. I need to: check whether a default html browser is opened; check whether the browser is minimized/maximized (simply, a window's state); get an url address typed in the browser. If any of these conditions is not met, I have to open the browser in a maximized view with a desired url address. I primarily wanted to do all this in Java, but it came to my mind that I should employ many techniques/technologies and combine them appropriately to complete the functionality. But, which ones? That's the problem. I just recalled Windows API, but I'm not sure if it is of any help... Some users on another forum suggested that I should consider JNI (no experience at all)... I only know how to open a default browser (e.g. with use of the 'browse(URI uri)' method of the 'java.awt.Desktop' class) - that's too little to be proud of. Please give me some hints, maybe links to reasonable discussions, I would greatly appreciate any suggestions how to approach the problem.

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  • Adding objects to the environment at timed intervals

    - by david
    I am using an ArrayList to handle objects and at each interval of 120 frames, I am adding a new object of the same type at a random location along the z-axis of 60. The problem is, it doesn't add just 1. It depends on how many are in the list. If I kill the Fox before the time interval when one is supposed to spawn comes, then no Fox will be spawned. If I don't kill any foxes, it grows exponentially. I only want one Fox to be added every 120 frames. This problem never happened before when I created new ones and added them to the environment. Any insights? Here is my code: /**** FOX CLASS ****/ import env3d.EnvObject; import java.util.ArrayList; public class Fox extends Creature { private int frame = 0; public Fox(double x, double y, double z) { super(x, y, z); // Must use the mutator as the fields have private access // in the parent class setTexture("models/fox/fox.png"); setModel("models/fox/fox.obj"); setScale(1.4); } public void move(ArrayList<Creature> creatures, ArrayList<Creature> dead_creatures, ArrayList<Creature> new_creatures) { frame++; setX(getX()-0.2); setRotateY(270); if (frame > 120) { Fox f = new Fox(60, 1, (int)(Math.random()*28)+1); new_creatures.add(f); frame = 0; } for (Creature c : creatures) { if (this.distance(c) < this.getScale()+c.getScale() && c instanceof Tux) { dead_creatures.add(c); } } for (Creature c : creatures) { if (c.getX() < 1 && c instanceof Fox) { dead_creatures.add(c); } } } } import env3d.Env; import java.util.ArrayList; import org.lwjgl.input.Keyboard; /** * A predator and prey simulation. Fox is the predator and Tux is the prey. */ public class Game { private Env env; private boolean finished; private ArrayList<Creature> creatures; private KingTux king; private Snowball ball; private int tuxcounter; private int kills; /** * Constructor for the Game class. It sets up the foxes and tuxes. */ public Game() { // we use a separate ArrayList to keep track of each animal. // our room is 50 x 50. creatures = new ArrayList<Creature>(); for (int i = 0; i < 10; i++) { creatures.add(new Tux((int)(Math.random()*10)+1, 1, (int)(Math.random()*28)+1)); } for (int i = 0; i < 1; i++) { creatures.add(new Fox(60, 1, (int)(Math.random()*28)+1)); } king = new KingTux(25, 1, 35); ball = new Snowball(-400, -400, -400); } /** * Play the game */ public void play() { finished = false; // Create the new environment. Must be done in the same // method as the game loop env = new Env(); // Make the room 50 x 50. env.setRoom(new Room()); // Add all the animals into to the environment for display for (Creature c : creatures) { env.addObject(c); } for (Creature c : creatures) { if (c instanceof Tux) { tuxcounter++; } } env.addObject(king); env.addObject(ball); // Sets up the camera env.setCameraXYZ(30, 50, 55); env.setCameraPitch(-63); // Turn off the default controls env.setDefaultControl(false); // A list to keep track of dead tuxes. ArrayList<Creature> dead_creatures = new ArrayList<Creature>(); ArrayList<Creature> new_creatures = new ArrayList<Creature>(); // The main game loop while (!finished) { if (env.getKey() == 1 || tuxcounter == 0) { finished = true; } env.setDisplayStr("Tuxes: " + tuxcounter, 15, 0); env.setDisplayStr("Kills: " + kills, 140, 0); processInput(); ball.move(); king.check(); // Move each fox and tux. for (Creature c : creatures) { c.move(creatures, dead_creatures, new_creatures); } for (Creature c : creatures) { if (c.distance(ball) < c.getScale()+ball.getScale() && c instanceof Fox) { dead_creatures.add(c); ball.setX(-400); ball.setY(-400); ball.setZ(-400); kills++; } } // Clean up of the dead tuxes. for (Creature c : dead_creatures) { if (c instanceof Tux) { tuxcounter--; } env.removeObject(c); creatures.remove(c); } for (Creature c : new_creatures) { creatures.add(c); env.addObject(c); } // we clear the ArrayList for the next loop. We could create a new one // every loop but that would be very inefficient. dead_creatures.clear(); new_creatures.clear(); // Update display env.advanceOneFrame(); } // Just a little clean up env.exit(); } private void processInput() { int keyDown = env.getKeyDown(); int key = env.getKey(); if (keyDown == 203) { king.setX(king.getX()-1); } else if (keyDown == 205) { king.setX(king.getX()+1); } if (ball.getX() <= -400 && key == Keyboard.KEY_S) { ball.setX(king.getX()); ball.setY(king.getY()); ball.setZ(king.getZ()); } } /** * Main method to launch the program. */ public static void main(String args[]) { (new Game()).play(); } } /**** CREATURE CLASS ****/ /* (Parent class to Tux, Fox, and KingTux) */ import env3d.EnvObject; import java.util.ArrayList; abstract public class Creature extends EnvObject { private int frame; private double rand; /** * Constructor for objects of class Creature */ public Creature(double x, double y, double z) { setX(x); setY(y); setZ(z); setScale(1); rand = Math.random(); } private void randomGenerator() { rand = Math.random(); } public void move(ArrayList<Creature> creatures, ArrayList<Creature> dead_creatures, ArrayList<Creature> new_creatures) { frame++; if (frame > 12) { randomGenerator(); frame = 0; } // if (rand < 0.25) { // setX(getX()+0.3); // setRotateY(90); // } else if (rand < 0.5) { // setX(getX()-0.3); // setRotateY(270); // } else if (rand < 0.75) { // setZ(getZ()+0.3); // setRotateY(0); // } else if (rand < 1) { // setZ(getZ()-0.3); // setRotateY(180); // } if (rand < 0.5) { setRotateY(getRotateY()-7); } else if (rand < 1) { setRotateY(getRotateY()+7); } setX(getX()+Math.sin(Math.toRadians(getRotateY()))*0.5); setZ(getZ()+Math.cos(Math.toRadians(getRotateY()))*0.5); if (getX() < getScale()) setX(getScale()); if (getX() > 50-getScale()) setX(50 - getScale()); if (getZ() < getScale()) setZ(getScale()); if (getZ() > 50-getScale()) setZ(50 - getScale()); // The move method now handles collision detection if (this instanceof Fox) { for (Creature c : creatures) { if (c.distance(this) < c.getScale()+this.getScale() && c instanceof Tux) { dead_creatures.add(c); } } } } } The rest of the classes are a bit trivial to this specific problem.

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