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  • Are Thread.stop and friends ever safe in Java?

    - by Stephen C
    The stop(), suspend(), and resume() in java.lang.Thread are deprecated because they are unsafe. The Sun recommended work around is to use Thread.interrupt(), but that approach doesn't work in all cases. For example, if you are call a library method that doesn't explicitly or implicitly check the interrupted flag, you have no choice but to wait for the call to finish. So, I'm wondering if it is possible to characterize situations where it is (provably) safe to call stop() on a Thread. For example, would it be safe to stop() a thread that did nothing but call find(...) or match(...) on a java.util.regex.Matcher? (If there are any Sun engineers reading this ... a definitive answer would be really appreciated.) EDIT: Answers that simply restate the mantra that you should not call stop() because it is deprecated, unsafe, whatever are missing the point of this question. I know that that it is genuinely unsafe in the majority of cases, and that if there is a viable alternative you should always use that instead. This question is about the subset cases where it is safe. Specifically, what is that subset?

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  • Cant we use a Set or collection as a return type in GAE?

    - by user273422
    In my code i have used Set<Employees> as a return type to my function addEmp(). So, i m gettin an Compilation error. The Error is: Compiling module com.employeedepartmentgae.Employeedepartmentgae Refreshing module from source Validating newly compiled units Removing units with errors [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingServiceAsync.java' [ERROR] Line 6: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 18: Employee cannot be resolved to a type [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingService.java' [ERROR] Line 6: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 20: Employee cannot be resolved to a type [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/EmployeeWidget.java' [ERROR] Line 12: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 75: The method addEmp(String, String, String, AsyncCallback) from the type GreetingServiceAsync refers to the missing type Employee [ERROR] Line 75: The type new AsyncCallback(){} must implement the inherited abstract method AsyncCallback.onSuccess(Set) [ERROR] Line 75: Employee cannot be resolved to a type [ERROR] Line 94: The method onSuccess(Set) of type new AsyncCallback(){} must override or implement a supertype method [ERROR] Line 94: Employee cannot be resolved to a type [ERROR] Line 96: Employee cannot be resolved to a type [ERROR] Line 96: Employee cannot be resolved to a type [ERROR] Line 98: Employee cannot be resolved to a type Removing invalidated units [WARN] Compilation unit 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/Employeedepartmentgae.java' is removed due to invalid reference(s): [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/EmployeeWidget.java [WARN] Compilation unit 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/DepartmentWidget.java' is removed due to invalid reference(s): [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingService.java [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingServiceAsync.java Computing all possible rebind results for 'com.employeedepartmentgae.client.Employeedepartmentgae' Rebinding com.employeedepartmentgae.client.Employeedepartmentgae Checking rule [ERROR] Unable to find type 'com.employeedepartmentgae.client.Employeedepartmentgae' [ERROR] Hint: Previous compiler errors may have made this type unavailable [ERROR] Hint: Check the inheritance chain from your module; it may not be inheriting a required module or a module may not be adding its source path entries properly So please help me.....

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Database design (MySql)::should we put html data in text field inside database table or more efficie

    - by meyosef
    Hi, We building big Web Application and we use mysql, we want to make mysql database more fast. Some of us think if we will put message html body inside table and not inside text.txt in will make database heavy and not fast. Thanks, *Part of main table that hold message: option 1:hold html message body inside database message { id (int) subject (varchar) body (text) } option 2: hold html message body inside body1.txt file message { id (int) subject (varchar) file_body_path (varchar) } *

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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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  • database design: table with large amount of columns (50+) or many sub tables with small amount of co

    - by Guillaume
    In our oroject we already have a lots of tables (100+). Some of them contains a lot of columns (50-100) and we are facing the need of adding more columns from time to time. What do you think is best - from maintenance and performance point of view - to split these huge tables in smaller entities or to keep the tables the way they are ? We are using an ORM tools, so we don't need to write custom request.

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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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  • Having to insert a record, then update the same record warrants 1:1 relationship design?

    - by dianovich
    Let's say an Order has many Line items and we're storing the total cost of an order (based on the sum of prices on order lines) in the orders table. -------------- orders -------------- id ref total_cost -------------- -------------- lines -------------- id order_id price -------------- In a simple application, the order and line are created during the same step of the checkout process. So this means INSERT INTO orders .... -- Get ID of inserted order record INSERT into lines VALUES(null, order_id, ...), ... where we get the order ID after creating the order record. The problem I'm having is trying to figure out the best way to store the total cost of an order. I don't want to have to create an order create lines on an order calculate cost on order based on lines then update record created in 1. in orders table This would mean a nullable total_cost field on orders for starters... My solution thus far is to have an order_totals table with a 1:1 relationship to the orders table. But I think it's redundant. Ideally, since everything required to calculate total costs (lines on an order) is in the database, I would work out the value every time I need it, but this is very expensive. What are your thoughts?

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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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  • Design guide-lines for writing a Typed SQL Statement API ?

    - by this. __curious_geek
    Last night I came up to sometihng intersting while designing my new project that brought me to ask this qustion here. My project is supposed to follow Table Gateway pattern using tradional ADO.Net datasets for data access. I don't want to write plain queries in my data-access classes. So I came up with an idea of writing a parser kindaa api that exposes objects and methods to generate queries on the move based on my domain objects. Later I want this api to hook up to my Business objects and provide Typed SQL generator api right on the business object instances. Any idea or references how can I do this ? This seems very wide to start with that I'm compelled take your opinions here. Does there anything already exists that can do 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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  • Is there a standard SQL Table design for overriding 'big picture' default values with lower level de

    - by RichardHowells
    Here's an example. Suppose we are trying to calculate a service charge. Say sales in the USA attract a 10 dollar charge, sales in the UK attract a 20 dollar charge So far it's easy - we are starting to imagine a table that lists charges by country. Now lets assume that Alaska and Hawaii are treated as special cases they are both 15 dollars That suggests a table with states, Alaska and Hawaii are charged at 15, but presumably we need 48 (redundant) rows all saying 10. This gives us a maintainance problem, our user only wants to type 10 once NOT 48 times. It does not sit well with the UK either. The UK does not have states. Suppose we throw in another couple of cross cutting rules. If you order by phone there is a 10% supplement on the charge. If you order via the web there is a 10% discount. But for some reason best known to the owners of the business the web/phone supplement/discount are not applied in Hawaii. It seems to me that this is quite a common kind of problem and there is probably a well known arrangement of tables to store the data. Most cases get handled by broad brush answers, but there are some very detailed low level variations that give rise to a huge number of theoretical combinations, most of which are not used.

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