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  • Java - multithreaded access to a local value store which is periodically cleared

    - by Telax
    I'm hoping for some advice or suggestions on how best to handle multi threaded access to a value store. My local value storage is designed to hold onto objects which are currently in use. If the object is not in use then it is removed from the store. A value is pumped into my store via thread1, its entry into the store is announced to listeners, and the value is stored. Values coming in on thread1 will either be totally new values or updates for existing values. A timer is used to periodically remove any value from the store which is not currently in use and so all that remains of this value is its ID held locally by an intermediary. Now, an active element on thread2 may wake up and try to access a set of values by passing a set of value IDs which it knows about. Some values will be stored already (great) and some may not (sadface). Those values which are not already stored will be retrieved from an external source. My main issue is that items which have not already been stored and are currently being queried for may arrive in on thread1 before the query is complete. I'd like to try and avoid locking access to the store whilst a query is being made as it may take some time.

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  • Java Swing: Expanding TreeNode

    - by sarav
    Is there any way to get a reference to the JTree component from a DefaultMutableTreeNode? All I need is to expand the given treenode and its child nodes. I am planning to use the JTree.expandPath() but I only have the reference to the treenode. I'm new to Swing and any suggestions to achieve this are welcome.

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  • Many-to-Many Relationship (with properties) in Google App Engine for Java

    - by rvandervort
    I understand from the official documentation on unowned relationships that the app must use sets of Key objects on either side of the relationship. This makes perfect sense. Coming from many years of RDBM-style programming, though, I'm pretty confused about how I can model properties of that relationship itself. For example, if I have entities Category and Entry in my many-to-many relationship and would like to persist a dateAdded property, or some other data that are only relevant when both sides of the relationship are known. I suppose it would be possible to create a third class : CategoryEntry that links the two, but this seems like a kludge. What is the proposed way to model this kind of situation ?

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  • Java: Writing a DOM to an XML file (formatting issues)

    - by Vhaerun
    I'm using org.w3c XML API to open an existing XML file. I'm removing some nodes , and I'm adding others instead . The problem is that the new nodes that are added are written one after another , with no newline and no indentation what so ever. While it's true that the XML file is valid , it is very hard for a human to examnine it. Is there anyway to add indentation , or at least a newline after each node ?

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  • Java iterative vs recursive

    - by user1389813
    Can anyone explain why the following recursive method is faster than the iterative one (Both are doing it string concatenation) ? Isn't the iterative approach suppose to beat up the recursive one ? plus each recursive call adds a new layer on top of the stack which can be very space inefficient. private static void string_concat(StringBuilder sb, int count){ if(count >= 9999) return; string_concat(sb.append(count), count+1); } public static void main(String [] arg){ long s = System.currentTimeMillis(); StringBuilder sb = new StringBuilder(); for(int i = 0; i < 9999; i++){ sb.append(i); } System.out.println(System.currentTimeMillis()-s); s = System.currentTimeMillis(); string_concat(new StringBuilder(),0); System.out.println(System.currentTimeMillis()-s); } I ran the program multiple time, and the recursive one always ends up 3-4 times faster than the iterative one. What could be the main reason there that is causing the iterative one slower ?

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  • Help making a button open another app with Java/Android

    - by user569503
    I am trying to learn to make a simple app that opens a couple of other apps to eliminate the need for another apps. I just can't figure it out. From reading here and other places it seems this should work. Button batteryhistory = (Button)findViewById(R.string.BatteryHistoryButtonDialog); batteryhistory.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Intent i = new Intent(); ComponentName n = new ComponentName("com.android.settings", "com.android.settings.BatteryHistory"); i.setComponent(n); startActivity(i); Thanks so much for the help :D

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  • Java code compression and decompression of a string

    - by user1822710
    I am having a problem figuring how to check a string for the same characters in a row then count that same character in a row then printing it out then giving the location of the last occorance of that character count then printing it out then moving to the next character in the string that is different then the previous character and the program is case sensitive. So the input could be: aaaaAAAbbbddccc How would I compress this string to: a4A3b3d2c3 ? and then decompress it?

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  • Time not entered in mysql ? Java

    - by Nitesh Panchal
    Hello, I have a datetime field in mysql table and i am using JPA for persisting data but only date goes in database. Time always shows 00:00:00. What should i do? I am not doing any manipulation with Date. All i do is to assign new Date() to a variable and store it in database. What am i doing wrong?

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  • Rotation in a Vector2d class in Java

    - by wanstein
    I've been working on this for one hour, just can't get it. I have a Vector2d class: public class Vector2d { public double x = 0.0; public double y = 0.0; .... } This vector class has a rotate() method which is causing me trouble. The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here? public void rotate(double n) { this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); } This works: public void rotate(double n) { rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); x = rx; y = ry; } I just can't spot any difference there

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  • Container of Generic Types in java

    - by Cyker
    I have a generic class Foo<T> and parameterized types Foo<String> and Foo<Integer>. Now I want to put different parameterized types into a single ArrayList. What is the correct way of doing this? Candidate 1: public class MMM { public static void main(String[] args) { Foo<String> fooString = new Foo<String>(); Foo<Integer> fooInteger = new Foo<Integer>(); ArrayList<Foo<?> > list = new ArrayList<Foo<?> >(); list.add(fooString); list.add(fooInteger); for (Foo<?> foo : list) { // Do something on foo. } } } class Foo<T> {} Candidate 2: public class MMM { public static void main(String[] args) { Foo<String> fooString = new Foo<String>(); Foo<Integer> fooInteger = new Foo<Integer>(); ArrayList<Foo> list = new ArrayList<Foo>(); list.add(fooString); list.add(fooInteger); for (Foo foo : list) { // Do something on foo. } } } class Foo<T> {} In a word, it is related to the difference between Foo<?> and the raw type Foo. Update: Grep What is the difference between the unbounded wildcard parameterized type and the raw type? on this link may be helpful.

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  • question about timestamp with timezone in postgresql+java?

    - by ylazez
    hey guys i have a column in the database(postgresql) i want to insert the current time in GMT in this column when getting the current time and inserting it into the DB it's inserted in the server timezone GMT-5 although that time was in GMT+0 any ideas how to insert this time in the database in GMT timezone ?

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  • concurrentmodificationexception hashmap in java

    - by chetan
    I write following code but when this run it generate concurrentmodificationexception if( attendancePolicy.getType().equals( AttendanceConstants.EMPLOYEE_ATTENDANCE_POLICY ) ) { synchronized( attendancePolicy.getListEmployee() ) { for( EmployeeAttendancePolicy employeeAttendancePolicy : attendancePolicy.getListEmployee() ) { employeeInfo = employeeInfoSessionBeanLocal.findEmployeeInfoEntityByEmployeeInfoId( employeeAttendancePolicy.getEmployeeId() ); if( employeeInfo != null ) { employeeAttendancePolicy.setEmpName( employeeInfo.getFirstName() + " " + employeeInfo.getMiddleName() + " " + employeeInfo.getLastName() ); company = companySessionBeanLocal.findCompanyById( employeeInfo.getCompanyId() ); employeeAttendancePolicy.setCompanyName( company.getName() ); department = departmentSessionBeanLocal.findDepartmentEntityByDepartmentId( employeeInfo.getDepartmentId() ); employeeAttendancePolicy.setDepartmentName( department.getName() ); } else { attendancePolicy.getListEmployee().remove( employeeAttendancePolicy ); } } } }

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  • pls give reason why this java program always comes to the else part

    - by Anbu
    public class Test { public static void main(String[] args){ if (5.0 5) // (5.0<5) for both case it is going to else System.out.println("5.0 is greater than 5"); else System.out.println("else part always comes here"); /another sample/ if (5.0 == 5) System.out.println("equals"); else System.out.println("not equal"); } } can any one explain the first "if statement" why it always come to else part

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  • Simple Java web application on Tomcat

    - by EugeneP
    If we only need to graphically authorize a user, view a few tables representation (from database), ability to change data in the database visually what tools to use to write such a web application that will run on Tomcat? What framework allows to do that in the most straightforward, easy-to-manage and elegant way?

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  • Web Service Security java

    - by WhoAmI
    My web service was created some time back using IBM JAX-RPC. As a part of enhancement, I need to provide some security to the existing service. One way is to provide a handler, all the request and response will pass through that handler only. In the request I can implement some authentication rules for each and every application/user accessing it. Other than this, What are the possible ways for securing it? I have heard someting called wsse security for web service. Is it possible to implement it for the JAX-RPC? Or it can be implemented only for JAX-WS? Need some helpful inputs on the wsse security so that i can jump learning it. Other than handler and wsse security, any other possible way to make a service secure? Please help.

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  • How to tell if there is an available thread in a thread pool in java

    - by Gormcito
    I am trying to proccess a queue of tasks from a database table as fast as possible while also limiting the number of threads to process the tasks. I am using a fixed sized thread pool with Executors.newFixedThreadPool(N); I want to know if there is a way of knowing if the thread pool is full, by that I mean are there currently 50 threads running, if so then I'll wait for a thread to be available before starting a new one instead of sleeping the main thread. Code of what I would like to do: ExecutorService executor = Executors.newFixedThreadPool(N); ResultSet results; while( true ) { results = getWaitingTasksStmt.executeQuery(); while( results.next() && executor.notFull() ) { executor.submit( new thread( new runnableInheritedClass(results) ) ); } }

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  • Regular expression one or more times JAVA

    - by user1381564
    Hi i am trying to match a string against a pattern this is the possible string signal CS, NS, dl: stateType := writeOrRead0; signal CS, pS : stateType := writeOrRead0; signal dS : stateType := writeOrRead0; i am only concerned with the pattern as far as the first colon. but the number of signals define can be more than one it could be three or four even this is the regular expression i have ^signal\\s*(\\w+),*\\s*(\\w+)\\s*: it will pick up the second two signal but and for the second one it picks up CS and pS and but the d and S in the next signal when i use matcher.group() come up seperately Can anyone give me an expression that will pick up all signal names whether there is one two three or more?

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  • Java: How to store Vector<String[]> in XML (or save in any other way)

    - by hatboysam
    Basically I have a proof-of-concept application that is a digital recipe book. Each Recipe is an object and each object has, among other fields, a Vector containing arrays. The Vector is the list of all ingredients in the Recipe while each ingredient has an array showing the name of the ingredient, the amount, and the unit for that amount. I want to save each Recipe to XML so that they can be accessed by the user. How can I store a Vector of String arrays in XML or any other sort of file so that it can later be recalled and accessed?

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  • Java: GatheringByteChannel advantages?

    - by Jason S
    I'm wondering when the GatheringByteChannel's write methods (taking in an array of ByteBuffers) have advantages over the "regular" WritableByteChannel write methods. I tried a test where I could use the regular vs. the gathering write method on a FileChannel, with approx 400KB/sec total in ByteBuffers of between 23-27 bytes in length in both cases. Gathering writes used an array of 64. The regular method used up approx 12% of my CPU, and the gathering method used up approx 16% of my CPU (worse than the regular method!) This tells me it's NOT useful to use gathering writes on a FileChannel around this range of operating parameters. Why would this be the case, and when would you ever use GatheringByteChannel? (on network I/O?) Relevant differences here: public void log(Queue<Packet> packets) throws IOException { if (this.gather) { int Nbuf = 64; ByteBuffer[] bbufs = new ByteBuffer[Nbuf]; int i = 0; Packet p; while ((p = packets.poll()) != null) { bbufs[i++] = p.getBuffer(); if (i == Nbuf) { this.fc.write(bbufs); i = 0; } } if (i > 0) { this.fc.write(bbufs, 0, i); } } else { Packet p; while ((p = packets.poll()) != null) { this.fc.write(p.getBuffer()); } } }

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  • Java Wicket - Calling javascript ( JQuery ) before AJAX

    - by user1428051
    I got this thing i'm trying to solve: I got a ListView created using Wicket ( 1.5 ) with a lot of elements and a scroll. When new items are available, the user is asked if he would like to refresh the list via a message backed by an AjaxLink: public void onClick(AjaxRequestTarget ajaxTarget) { /* do something ... */ ajaxTarget.addComponent(_list); } So on click the list gets reloaded and the scroll position is reset to zero. Is there any way i can call JavaScript before the list reloads the save the scroll position? (I know how to get/save the scroll position ( .scrollTop() ) , i just don't know how to call a function right before AJAX ).

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  • how to get the PageFormat from a Java.awt.print.PrinterJob

    - by Alex
    Hi, I'm trying to use the PageFormat information to modify my javax.swing based printout prior to printing it. I am stumped as to how I can get the PageFormat from the PrintJob (which is obtained using getPrinterJob() and printDialog()). I know there is the getPageFormat method, but I can't figure out how to get the PrintRequestAttributeSet (which is not the printJob.getPrintService().getPrintAttributes()). Honestly, all I really want to know is the width and height of the page. Any ideas on how I can do that? Thanks.

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