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  • How to find out efficiently the auto-generated id for a new object when using JPA?

    - by webstarg
    Hello, I have an attribute which is annotated with @Id. The ID is going to be generated automatically when persisting the object. That means that the ID-value is not defined before I persist the object. After persisting it, it has an ID (in the database), but unfortunately the field still remains null as long as I don't reload it from the DB. is there any easy way to find out the generated id? Or better: To configure that it will be written into the field? Thanks in advance

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  • Does march have 32 days?

    - by santhan
    Once I found march showing 32 days in JCalendar. The critical part here is this condition seems to be transient. I couldn't reproduce this in a consistent fashion. Has anyone seen this before?? Any fixes possible?? Many thanks in advance!

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  • Help choosing the right data structure

    - by devoured elysium
    I need a data structure with the following requirements: Needs to be able to get elements by index (like a List). I will always just add / remove elements from the end of the structure. I am inclined to use an ArrayList. In this situation, it seems to be O(1) both to read elements (they always are?), remove elements (I only need to remove them at the end of the list) and to add(I only add to the end of the list). There is only the problem that time to time the ArrayList will have a performance penalty when it's completly full and I need to add more elements to it. Is there any other better idea? I don't think of a data structure that'd beat the ArrayList here. Thanks

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  • Find messages from certain key till certain key while being able to remove stale keys.

    - by Alfred
    My problem Let's say I add messages to some sort of datastructure: 1. "dude" 2. "where" 3. "is" 4. "my" 5. "car" Asking for messages from index[4,5] should return: "my","car". Next let's assume that after a while I would like to purge old messages because they aren't useful anymore and I want to save memory. Let's say at time x messages[1-3] became stale. I assume that it would be most efficient to just do the deletion once every x seconds. Next my datastructure should contain: 4. "my" 5. "car" My solution? I was thinking of using a concurrentskiplistset or concurrentskiplist map. Also I was thinking of deleting the old messages from inside a newSingleThreadScheduledExecutor. I would like to know how you would implement(efficiently/thread-safe) this or maybe use a library?

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  • Where should I put interface?

    - by Roman
    I program a class in which I have a method which takes an callback object from an external software. At the moment Eclipse says that it does not know the type of the object I gave as argument (it is expectable since I do not specify this type, it's done by the external software). So, I think I need to write an interface for the object which I give as an argument to my method. In this respect I have two questions. Is it really so? Can I solve the mentioned problem in the mentioned way. If it is the case, where should I put this interface? In the same file where my class is? In the class? Outside of the class?

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  • JNI - native method with ByteBuffer parameter

    - by Ajan
    I've got a method: public native void doSomething(ByteBuffer in, ByteBuffer out); Generated by javah C/C++ header of this method is: JNIEXPORT void JNICALL Java__MyClass_doSomething (JNIEnv *, jobject, jobject, jobject, jint, jint); How can I get a data array from jobject (that is a ByteBuffer instance) ?

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  • How do I change the build's SDK version in Xcode?

    - by Kavon Farvardin
    I'm using Xcode 2.5 on Mac 10.4.11 PPC. javac -version returns 1.5.x yet when I imported my source code and tried to build it in Xcode, I get errors all over because generics, annotations, and for-each loops are not supported in -source 1.3. I thought I found the setting to change the source version in Xcode in the above but it doesn't work. Any ideas?

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  • create an hotspot and set an image without background (like earth icon) to my panel

    - by sirvan
    Hi I try to create an hotspot by Extends of canvas and I try to add it on a panel witch painted by images , so I must to draw an icon (image) instead of clear rectangle of the screen, to do that I override the paint method to draw the icon I want to use, so far there is no problem, the hotspot work true and the icon painted in true size I want(32,24 pixel) I try to add this hotspot after painting image on the my panel in mypanel.paint(g) that override too. The problem , I use an car icon that have no background !!(I hope you can understand me) just car icon must be show on the panel that painted with my images; But an unwanted rectangle created around the icon and made bad view, How I can paint may icon on panel without that background? Please help me.

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  • Blackberry Contacts Photo

    - by Farhan
    Hi, I am currently working on the Application named (Blackberry Contacts Sync) and i am stuck at this point that how i sync Contact's Image. Please tell me how to store images in Database(MySQL) and how to retrieve it.

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  • Can we instantiate abstract class?

    - by satheesh.droid
    I don't understand whether we can instantiate abstract class by any means because I have read we can inherit the abstract class but in have found we can create an object by calling method of other class.For example LocationProvider is an abstract class but we can create object for the same by calling getProvider() function in LocationManager class. By the following code LocationManager lm=getSystemService(Context.LOCATION_PROVIDER) LocationProvider lp=lm.getProvider("gps");

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  • replace capturing group

    - by Don
    Hi, If I have a regex with a capturing group, e.g. foo(_+f). If I match this against a string and want to replace the first capturing group in all matches with baz so that foo___f blah foo________f is converted to: foobaz blah foobaz There doesn't appear to be any easy way to do this using the standard libraries. If I use Matcher.replaceAll() this will replace all matches of the entire pattern and convert the string to baz blah baz Obviously I can just iterate through the matches, store the start and end index of each capturing group, then go back and replace them, but is there an easier way? Thanks, Don

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  • How to remove an element from set using Iterator?

    - by ankit
    I have a scenario that I am iterating over a set using iterator. Now I want to remove 1st element while my iterator is on 2nd element. How can I do it. I dont want to convert this set to list and using listIterator. I dont want to collect all objects to be removed in other set and call remove all sample code. Set<MyObject> mySet = new HashSet<MyObject>(); mySet.add(MyObject1); mySet.add(MyObject2); ... Iterator itr = mySet.iterator(); while(itr.hasNext()) { // Now iterator is at second element and I want to remove first element }

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  • Does allocation speed depend on the garbage collector being used?

    - by jkff
    My app is allocating a ton of objects (1mln per second; most objects are byte arrays of size ~80-100 and strings of the same size) and I think it might be the source of its poor performance. The app's working set is only tens of megabytes. Profiling the app shows that GC time is negligibly small. However, I suspect that perhaps the allocation procedure depends on which GC is being used, and some settings might make allocation faster or perhaps make a positive influence on cache hit rate, etc. Is that so? Or is allocation performance independent on GC settings under the assumption that garbage collection itself takes little time?

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  • Passing.getText() String to another class

    - by DanMc
    I'm currently working on a first year university project and I have a problem, although I doubt it's a very complicated one, but I've been searching and I just can't find a suitable answer to it. The problem concerns two classes. A gui class (class1) and another class (class2). I have a JTextField in class1 and am trying to pass through the .getText() value to class2 and store it in a String type variable. The current code I'm trying to achieve this with is the following: (Class1) private JTextField textField = new JTextField("Something"); ... public String getTextFieldString() { return textField.getText(); } (Class2) private c1 Class1 = new Class1(); private String s = new String(); ... s = c1.getTextFieldString(); I'm pretty new to coding, I've read that maybe I need to pass through an argument somewhere and I assume that's because textField is not static in itself, it changes when somebody enters a new value. (sorry for stating the obvious there.) Anyway, help is appreciated. Thanks a lot!

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  • How to trigger an application in mobile automatically

    - by san6086
    My idea is to make an application start automatically when a message from a specific user reaches the inbox of the mobile . For example if my friend sends some numbers to my mobile, the sms has to be read and validated first and then calculator ( inbuilt mobile application) has to be triggered and process the numbers from the message. Please help me with the above query.

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  • doubt in Exceptions

    - by Ajay Singh
    class MyException extends Exception { MyException() {} MyException(String msg) { super(msg);} } public class NewException { static void f() throws MyException { System.out.println("throwing exception from f()"); throw new ClassCastException(); } static void g() throws MyException { System.out.println("throwing exception from g()"); throw new MyException("parametrized "); } public static void main(String ...strings ) { try { f(); } catch(MyException e) { e.printStackTrace(System.out); } try { g(); } catch(MyException e) { e.printStackTrace(System.out); } } } In the function f() iam specifying that "MyException " exception will be thrown and actually iam throwing some other exception which has no relation with MyException but still the compiler does not report any complain.Why is it so??

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  • What are the suggested alternatives for Class<T>.isAssignableFrom(Class<?> cls)?

    - by Wing C. Chen
    Currently I am doing the profiling to a piece of code. During the profiling, I discovered that this very method call, Class<T>.isAssignableFrom(Class<?> cls) takes up to quite amount of the entire time. Because this is a method from reflection, it takes a lot of time compared to normal keywords or method calls. I am wondering if there are some good alternatives for this method calls?

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  • Does it mean JVM Suspended?

    - by Joe.wang
    When my application run . I got a message says : Ping: Timed out waiting for signal from JVM. The JVM was launched with debug options so this may be because the JVM is currently suspended by a debugger. Any future timeouts during this JVM invocation will be silently ignored. What does that mean? It seems it will block any web request from outside? because when I upload a file to it, it failed. help me .

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  • Does thread pool size keep growing for scheduledthreadpoolexecutor?

    - by Sourajit Basak
    Imagine a situation where tasks are being added to scheduledthreadpoolexecutor. Each of these tasks will keep on running at different periodic intervals. Although all such tasks will not be running at the same time because each is set at different intervals, there may be a situation where a high number of threads are competing for execution. Is there any restriction on total number of threads ? It seems there is a restriction on the total number of idle threads. And does this concept of idle thread imply that long running tasks (thread) may be destroyed and recreated when needed ?

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  • Interview question : What is the fastest way to generate prime number recursively ?

    - by hilal
    Generation of prime number is simple but what is the fastest way to find it and generate( prime numbers) it recursively ? Here is my solution. However, it is not the best way. I think it is O(N*sqrt(N)). Please correct me, if I am wrong. public static boolean isPrime(int n) { if (n < 2) { return false; } else if (n % 2 == 0 & n != 2) { return false; } else { return isPrime(n, (int) Math.sqrt(n)); } } private static boolean isPrime(int n, int i) { if (i < 2) { return true; } else if (n % i == 0) { return false; } else { return isPrime(n, --i); } } public static void generatePrimes(int n){ if(n < 2) { return ; } else if(isPrime(n)) { System.out.println(n); } generatePrimes(--n); } public static void main(String[] args) { generatePrimes(200); }

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  • Extract elements from list based on object property type

    - by Dustin Digmann
    Often, I have a list of objects. Each object has properties. I want to extract a subset of the list where a specific property has a predefined value. Example: I have a list of User objects. A User has a homeTown. I want to extract all users from my list with "Springfield" as their homeTown. I normally see this accomplished as follows: List users = getTheUsers(); List returnList = new ArrayList(); for (User user: users) { if ("springfield".equalsIgnoreCase(user.getHomeTown()) returnList.add(user); } I am not particularly satisfied with this solution. Yes, it works, but it seems so slow. There must be a non-linear solution. Suggestions?

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