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  • "Abstract static" method - how?

    - by polyglot
    There are already several SO questions on why there is not abstract static method/field as such, but I'm wondering about how one would go about implementing the following psuedo-code: class Animal { abstract static int getNumberOfLegs(); // not possible } class Chicken inherits Animal { static int getNumberOfLegs() { return 2; } class Dog inherits Animal { static int getNumberOfLegs() { return 4; } Here is the problem: Assuming that I want make sure that every class that inherits Animal to contain getNumberOfLegs() method (i.e. almost like an interface, except I do want the abstract class to implement several methods that are common to all child classes, hence pure interface does not work here). getNumberOfLegs() obviously should be a static method (assuming that in a perfect world we dont' have crippled chicken and dogs so getNumberOfLegs is not instance-dependent). Without an "abstract static" method/field, one can either leave the method out from Animal class, then there is the risk that some child class do not have that method. Or one can make getNumberOfLegs an instance method, but then one would have to instantiate a class to find out how many legs that animal has - even though it is not necessary. How do one usually go about implementing this situation?

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  • adding elements in to the doubly linked list

    - by user329820
    Hi this is my code for main class and doubly linked class and node class but when I run the program ,in the concole will show this"datastructureproject.DoublyLinkedList@19ee1ac" instead of the random numbers .please help me thanks! main class: public class Main { public static int getRandomNumber(double min, double max) { Random random = new Random(); return (int) (random.nextDouble() * (max - min) + min); } public static void main(String[] args) { int j; int i = 0; i = getRandomNumber(10, 10000); DoublyLinkedList listOne = new DoublyLinkedList(); for (j = 0; j <= i / 2; j++) { listOne.add(getRandomNumber(10, 10000)); } System.out.println(listOne); } } doubly linked list class: public class DoublyLinkedList { private Node head ; private Node tail; private long size = 0; public DoublyLinkedList() { head= new Node(0, null, null); tail = new Node(0, head, null); } public void add(int i){ head.setValue(i); Node newNode = new Node(); head.setNext(newNode); newNode.setPrev(head); newNode = head; } } and the node class is like the class that you have seen before (Node prev,Node next,int value)

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  • Making an efficient algorithm

    - by James P.
    Here's my recent submission for the FB programming contest (qualifying round only requires to upload program output so source code doesn't matter). The objective is to find two squares that add up to a given value. I've left it as it is as an example. It does the job but is too slow for my liking. Here's the points that are obviously eating up time: List of squares is being recalculated for each call of getNumOfDoubleSquares(). This could be precalculated or extended when needed. Both squares are being checked for when it is only necessary to check for one (complements). There might be a more efficient way than a double-nested loop to find pairs. Other suggestions? Besides this particular problem, what do you look for when optimizing an algorithm? public static int getNumOfDoubleSquares( Integer target ){ int num = 0; ArrayList<Integer> squares = new ArrayList<Integer>(); ArrayList<Integer> found = new ArrayList<Integer>(); int squareValue = 0; for( int j=0; squareValue<=target; j++ ){ squares.add(j, squareValue); squareValue = (int)Math.pow(j+1,2); } int squareSum = 0; System.out.println( "Target=" + target ); for( int i = 0; i < squares.size(); i++ ){ int square1 = squares.get(i); for( int j = 0; j < squares.size(); j++ ){ int square2 = squares.get(j); squareSum = square1 + square2; if( squareSum == target && !found.contains( square1 ) && !found.contains( square2 ) ){ found.add(square1); found.add(square2); System.out.println( "Found !" + square1 +"+"+ square2 +"="+ squareSum); num++; } } } return num; }

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  • What is an appropriate way to separate lifecycle events in the logging system?

    - by Hanno Fietz
    I have an application with many different parts, it runs on OSGi, so there's the bundle lifecycles, there's a number of message processors and plugin components that all can die, can be started and stopped, have their setup changed etc. I want a way to get a good picture of the current system status, what components are up, which have problems, how long they have been running for etc. I think that logging, especially in combination with custom appenders (I'm using log4j), is a good part of the solution and does help ad-hoc analysis as well as live monitoring. Normally, I would classify lifecycle events as INFO level, but what I really want is to have them separate from what else is going on in INFO. I could create my own level, LIFECYCLE. The lifecycle events happen in various different areas and on various levels in the application hierarchy, also they happen in the same areas as other events that I want to separate them from. I could introduce some common lifecycle management and use that to distinguish the events from others. For instance, all components that have a lifecycle could implement a particular interface and I log by its name. Are there good examples of how this is done elsewhere? What are considerations?

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  • Twitter rss feed 401 - unauthorisation

    - by RenegadeAndy
    Hey. I have a public twitter account and this is the rss feed for it: http://twitter.com/statuses/friends_timeline/150784631.rss The problem is, im getting an http 401 whenever im trying to access it. Can anybody explain how to stop this - and get it to work either with authentication or without! Cheers

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  • BeanUtils getPropertyOfMapBean

    - by dx-cp
    Hi, Im wondering if it is possible to get data from property which is map cotaining pairs Key-StringArray (Map) in BeanUtils library. I just simply need to access one of array elements by calling propertyName=string[0]. Current version (1.8.3) does not support indexed properties. If you look into their code you will find in class PropertyUtilsBean in method getPropertyOfMapBean: if (resolver.isIndexed(propertyName) || resolver.isMapped(propertyName)) { throw new IllegalArgumentException( "Indexed or mapped properties are not supported on" + " objects of type Map: " + propertyName); } way too bad:-( Have any of you any tip how to do it somehow differently?

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  • Complete list of Fonts which support

    - by Yan Cheng CHEOK
    Currently, if I change the locale setting of my application by Locale.setDefault(Locale.ENGLISH); Locale.setDefault(Locale.SIMPLIFIED_CHINESE); What I understand from this JFreeChart forum is that, I am not using correct font. Once you get the reference of the LegentTitle, you can set it to any font. Apparently, JFreeChart's default is "Tahoma" and it doesn't support Chinese characters. May I know, how I can programmatic determine, as list of available Fonts in my system, which support Chinese? I can hard code it to Serif (It fully support Chinese, doesn't it?), its look n feel doesn't looks good to me. I would like to have more choices.

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  • Eclipselink and update trigger on multiple access to the database

    - by Raven
    Hi, in my project I have a database which many clients connect to. Concurrent access and writing works well. The problem now is not to reload the data every second from the database to always have the current status of the data. Does Eclipselink provide a trigger mechanism on (automatically?) reload the data if the database is changed? How would one use this trigger? Thanks!

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  • What happens if an exception is thrown during finalize()

    - by Psykocyber
    What would happen if an exception is thrown during the execution of finalize()? Is the stack unwind like normally? Does it continue finalize() and ignore the exception? Does it stop finalize() and continue GC the object? Or something else? I'm not looking for guidelines of using finalize() there are plently of pages explaining that.

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  • I have a feeling that adding fields marked with @Transient annotation to entity is very bug-prone. A

    - by Roman
    I have some philosophical feeling that adding to an entity fields which doesn't mapped to the DB is a wrong way of solving problems. But are there any concrete situations where using @Transient fields leads to implicit and hard fixing problems? For example, is it possible that adding/removing 2nd level cache will break our app when there are @Transient fields in our entities?

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  • Is there programming language with better approach for switch's break statements ?

    - by Vitaly Polonetsky
    It's the same syntax in a way too many languages: switch (someValue) { case OPTION_ONE: case OPTION_LIKE_ONE: case OPTION_ONE_SIMILAR: doSomeStuff1(); break; // EXIT the switch case OPTION_TWO_WITH_PRE_ACTION: doPreActionStuff2(); // the default is to CONTINUE to next case case OPTION_TWO: doSomeStuff2(); break; // EXIT the switch case OPTION_THREE: doSomeStuff3(); break; // EXIT the switch } Now all you know that break statements are required, because the switch will continue to the next case when break statement is missing. We have an example of that with OPTION_LIKE_ONE, OPTION_ONE_SIMILAR and OPTION_TWO_WITH_PRE_ACTION. The problem is that we only need this "skip to next case" very very very rarely. And very often we put break at the end of case. It very easy for a beginner to forget about it. And one of my C teachers even explained it to us as if it was a bug in C language (don't want to talk about it :) I would like to ask if there are any other languages that I don't know of (or forgot about) that handle switch/case like this: switch (someValue) { case OPTION_ONE: continue; // CONTINUE to next case case OPTION_LIKE_ONE: continue; // CONTINUE to next case case OPTION_ONE_SIMILAR: doSomeStuff1(); // the default is to EXIT the switch case OPTION_TWO_WITH_PRE_ACTION: doPreActionStuff2(); continue; // CONTINUE to next case case OPTION_TWO: doSomeStuff2(); // the default is to EXIT the switch case OPTION_THREE: doSomeStuff3(); // the default is to EXIT the switch } The second question: is there any historical meaning to why it is like this in C? May be continue to next case was used far more often than we use it these days ?

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  • Must JDBC Resultsets and Statements be closed separately although the Connection is closed afterwards?

    - by Mulmoth
    It is said to be a good habit to close all JDBC resources after usage. But if I have the following code, is it necessary to close the Resultset and the Statement? Connection conn = null; PreparedStatement stmt = null; ResultSet rs = null; try { conn = // Retrieve connection stmt = conn.prepareStatement(// Some SQL); rs = stmt.executeQuery(); } catch { // Error Handling } finally { try { if (rs != null) rs.close(); } catch (Exception e) {}; try { if (stmt != null) stmt.close(); } catch (Exception e) {}; try { if (conn != null) conn.close(); } catch (Exception e) {}; } The question is if the closing of the connection does the job or if it leaves some resources in use.

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  • graphing amplitude

    - by John
    I was wondering if someone could point me to a good tutorial or show me how to graph the amplitude from a bytearray. The audio format I am using is: ULAW 8000.0 Hz, 8 bit, mono, 1 bytes/frame.

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  • How do I limit JPQ output?

    - by den-javamaniac
    I need to limit number of entities returned by a query to some certain value inside a JPA query (through JPQL). Particularly: select m from Manual m //constraint e.g. in sql (mysql syntax) I would do it like: select * from Manual limit 1 The only solution that comes up is simply to get all entities and then choose first one, which is out of the issue. Any ideas?

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  • JUnit : Is there a way to skip a test belonging to a Test class's parent?

    - by Jon
    I have two classes: public abstract class AbstractFoobar { ... } and public class ConcreteFoobar extends AbstractFoobar { ... } I have corresponding test classes for these two classes: public class AbstractFoobarTest { ... } and public class ConcreteFoobarTest extends AbstractFoobarTest { ... } When I run ConcreteFoobarTest (in JUnit), the annotated @Test methods in AbstractFoobarTest get run along with those declared directly on ConcreteFoobarTest because they are inherited. Is there anyway to skip them?

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  • custom ListView --Null pointer exception

    - by raghs
    this code throws a Null pointer exception. It was thrown by getChildAt(i). The getCount() returns the number of items in listView. But getChildAt(i) returns only if item is present in current list view. For example in a scrollable list view assume that there are 20 items. The getCount() returns 20. But getChildAt(20) returns null. Because it doesnot fit in listview. How to solve this problem?? int i,j=object.getCount(); View v=getListView(); CheckBox chk=null; for(i=0;i<j;i++) { chk=((CheckBox)((ViewGroup) v).getChildAt(i).findViewById(R.id.checkBox1)); if(chk.isChecked()) { //download the contents to specific folder in sd card } }

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  • Iterate over a list and put data in hashmap

    - by sarah
    I am having a list where i need to loop over it and put its data in hashmap,i am using this approach for(int i=0;i<list.size();i++) { HashMap hMap=new HashMap(); hMap.put("Data", list); } But when i need to read the value from hMap i am doing in this way Collection c = hMap.values(); Iterator itr = c.iterator(); while(itr.hasNext()) { System.out.println("next val is--"+itr.next()); } next vali is--- is printed in com.bean.xyz@23032bc[id=1] format ,i need the exact data,how will i do this ?

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  • Android Sqlite - obtaining the correct database row id

    - by Dan_Dan_Man
    I'm working on an app that allows the user to create notes while rehearsing a play. The user can view the notes they have created in a listview, and edit and delete them if they wish. Take for example the user creates 3 notes. In the database, the row_id's will be 1, 2 and 3. So when the user views the notes in the listview, they will also be in the order 1, 2, 3 (intially 0, 1, 2 before I increment the values). So the user can view and delete the correct row from the database. The problem arises when the user decides to delete a note. Say the user deletes the note in position 2. Thus our database will have row_id's 1 and 3. But in the listview, they will be in the position 1 and 2. So if the user clicks on the note in position 2 in the listview it should return the row in the database with row_id 3. However it tries to look for the row_id 2 which doesn't exist, and hence crashes. I need to know how to obtain the corresponding row_id, given the user's selection in the listview. Here is the code below that does this: // When the user selects "Delete" in context menu public boolean onContextItemSelected(MenuItem item) { AdapterContextMenuInfo info = (AdapterContextMenuInfo) item .getMenuInfo(); switch (item.getItemId()) { case DELETE_ID: deleteNote(info.id + 1); return true; } return super.onContextItemSelected(item); } // This method actually deletes the selected note private void deleteNote(long id) { Log.d(TAG, "Deleting row: " + id); mNDbAdapter.deleteNote(id); mCursor = mNDbAdapter.fetchAllNotes(); startManagingCursor(mCursor); fillData(); // TODO: Update play database if there are no notes left for a line. } // When the user clicks on an item, display the selected note protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); viewNote(id, "", "", true); } // This is where we display the note in a custom alert dialog. I've ommited // the rest of the code in this method because the problem lies in this line: // "mCursor = mNDbAdapter.fetchNote(newId);" // I need to replace "newId" with the row_id in the database. private void viewNote(long id, String defaultTitle, String defaultNote, boolean fresh) { final int lineNumber; String title; String note; id++; final long newId = id; Log.d(TAG, "Returning row: " + newId); mCursor = mNDbAdapter.fetchNote(newId); lineNumber = (mCursor.getInt(mCursor.getColumnIndex("number"))); title = (mCursor.getString(mCursor.getColumnIndex("title"))); note = (mCursor.getString(mCursor.getColumnIndex("note"))); . . . } Let me know if you would like me to show anymore code. It seems like something so simple but I just can't find a solution. Thanks!

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