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  • Implementing java FixedTreadPool status listener

    - by InsertNickHere
    Hi there, it's about an application which is supposed to process (VAD, Loudness, Clipping) a lot of soundfiles (e.g. 100k). At this time, I create as many worker threads (callables) as I can put into memory, and then run all with a threadPool.invokeAll(), write results to file system, unload processed files and continue at step 1. Due to the fact it's an app with a GUI, i don't want to user to feel like the app "is not responding" while processing all soundfiles. (which it does at this time cause invokeAll is blocking). Im not sure what is a "good" way to fix this. It shall not be possible for the user to do other things while processing, but I'd like to show a progress bar like "10 of 100000 soundfiles are done". So how do I get there? Do I have to create a "watcher thread", so that every worker hold a callback on it? I'm quite new to multi threading, and don't get the idea of such a mechanisem.. If you need to know: I'm using SWT/JFace. Regards, InsertNickHere

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  • Java HashSet using a specified method

    - by threenplusone
    I have a basic class 'HistoryItem' like so: public class HistoryItem private Date startDate; private Date endDate; private Info info; private String details; @Override public int hashCode() { int hash = (startDate == null ? 0 : startDate.hashCode()); hash = hash * 31 + (endDate == null ? 0 : endDate.hashCode()); return hash; } } I am currently using a HashSet to remove duplicates from an ArrayList on the startDate & endDate fields, which is working correctly. However I also need to remove duplicates on different fields (info & details). My question is this. Is there a way to specify a different method which HashSet will use in place of hashCode()? Something like this: public int hashCode_2() { int hash = (info == null ? 0 : info.hashCode()); hash = hash * 31 + (details == null ? 0 : details.hashCode()); return hash; } Set<HistoryItem> removeDups = new HashSet<HistoryItem>(); removeDups.setHashMethod(hashCode_2); Or is there another way that I should be doing this?

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  • Read Java in as Hex

    - by James
    Hi, I have tried to solve this but I keep coming up with stuff that is no help I'm sure this is easy (when you know how of course ;) ) What I would like to do is read in a file using a byte stream like below: while((read = in.read()) != -1){ //code removed to save space Integer.toHexString(read); System.out.println(read); } When it prints out the Hex to the screen it will print out numbers fine e.g 31 13 12 0 but when it comes to a hex code that should be 01 31 it will print 0 131. I want to read it in to a variable like you would see in a hex editor i.e 00 11 21 31 no single numbers as i need to scan the whole file and look for patterns which I know how to do I'm just stuck on this :/ so in short i need a variabe to contain the two hex characters i.e int temp = 01 not int temp = 0 , I hope this all makes sense, I'm a little confused as it's 3am! If anyone knows how to do this I would be most greatful, p.s thanks for the help in advance this site has saved me loads of research and have learnt a lot! Many thanks.

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  • java singleton instantiation

    - by jurchiks
    I've found three ways of instantiating a Singleton, but I have doubts as to whether any of them is the best there is. I'm using them in a multi-threaded environment and prefer lazy instantiation. Sample 1: private static final ClassName INSTANCE = new ClassName(); public static ClassName getInstance() { return INSTANCE; } Sample 2: private static class SingletonHolder { public static final ClassName INSTANCE = new ClassName(); } public static ClassName getInstance() { return SingletonHolder.INSTANCE; } Sample 3: private static ClassName INSTANCE; public static synchronized ClassName getInstance() { if (INSTANCE == null) INSTANCE = new ClassName(); return INSTANCE; } The project I'm using ATM uses Sample 2 everywhere, but I kind of like Sample 3 more. There is also the Enum version, but I just don't get it. The question here is - in which cases I should/shouldn't use any of these variations? I'm not looking for lengthy explanations though (there's plenty of other topics about that, but they all eventually turn into arguing IMO), I'd like it to be understandable with few words.

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  • Java Clock Assignment

    - by Mike S
    For my assignment we are suppose to make a clock. We need variables of hours, minutes, and seconds and methods like setHours/getHours, setMinutes/getMinutes, setSeconds/getSeconds. Now the parts of the assignment that I am having trouble on is that we need a addClock() method to make the sum of two clock objects and a tickDown() method which decrements the clock object and a tick() method that increments a Clock object by one second. Lastly, the part where I am really confused on is, I need to write a main() method in the Clock class to test the functionality of your objects with a separate Tester class with a main() method. Here is what I have so far... public class Clock { private int hr; //store hours private int min; //store minutes private int sec; //store seconds //Default constructor public Clock () { setClock (0, 0, 0); } public Clock (int hours, int minutes, int seconds) { setTimes (hours, minute, seconds); } public void setClock (int hours, int minutes, int seconds) { if(0 <= hours && hours < 24) { hr = hours; } else { hr = 0; } if(0 <= minutes && minutes < 60) { min = minutes; } else { min = 0; } if(0 <= seconds && seconds < 60) { sec = seconds; } else { sec = 0; } } public int getHours ( ) { return hr; } public int getMinutes ( ) { return min; } public int getSeconds ( ) { return sec; } //Method to increment the time by one second //Postcondition: The time is incremented by one second //If the before-increment time is 23:59:59, the time //is reset to 00:00:00 public void tickSeconds ( ) { sec++; if(sec > 59) { sec = 0; tickMinutes ( ); //increment minutes } } public void tickMinutes() { min++; If (min > 59) { min = 0; tickHours(); //increment hours } } public void tickHours() { hr++; If (hr > 23) hr = 0; } }

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  • How is Java Process.getOutputStream() Implemented?

    - by Amit Kumar
    I know the answer depends on the particular JVM, but I would like to understand how it is usually implemented? Is it in terms of popen (posix)? In terms of efficiency do I need to keep something in mind (other than using a Buffered stream as suggested by the javadoc). I would be interested to know if there is a general reference about implementations of JVMs which answers such questions.

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  • java: how to convert a file to utf8

    - by Enrique San Martín
    Hi, i have a file that have some non-utf8 caracters (like "ISO-8859-1"), and so i want to convert that file (or read) to UTF8 encoding, how i can do it? The code it's like this: File file = new File("some_file_with_non_utf8_characters.txt"); /* some code to convert the file to an utf8 file */ ... edit: Put an encoding example

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  • java: relationship of the Runnable and Thread interfaces

    - by Karl Patrick
    I realize that the method run() must be declared because its declared in the Runnable interface. But my question comes when this class runs how is the Thread object allowed if there is no import call to a particular package? how does runnable know anything about Thread or its methods? does the Runnable interface extend the Thread class? Obviously I don't understand interfaces very well. thanks in advance. class PrimeFinder implements Runnable{ public long target; public long prime; public boolean finished = false; public Thread runner; PrimeFinder(long inTarget){ target = inTarget; if(runner == null){ runner = new Thread(this); runner.start() } } public void run(){ } }

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  • How to combine array list string in java ?

    - by tiendv
    I have some arraylist string with keyword inside like that ! A windows is arraylist string with keyword is bold Struct of window : 9 words before + keyword + 9 words after You can see some window overlaping How to i combine that arraylist to receive like that : Thanks

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  • Cookie questions in Java

    - by user220201
    Hi, How do I differentiate between multiple cookies set through my site? I am setting two kinds of cookies one to see if the user has visited the site or not and an other one for authentication. How do I differentiate between these two? I get both of them when someone accesses a page after authentication. Do I add extra information to the Cookie Value or is there some other way? I understand the setName() function will change the name (from jsessionid) for every cookie from then on. Am I correct? Pav

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  • how to generate a random String? in java

    - by chandra wibowo
    hi everyone, i have an object called Student, and it has studentName, studentId, studentAddress, etc. for the studentId, i have to generate random string consist of seven numeric charaters, eg. studentId = getRandomId(); studentId = "1234567" <-- from the random generator. and i have to make sure that there is no duplicate id. thanks in advance

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  • Should I catch exceptions thrown when closing java.sql.Connection

    - by jb
    Connection.close() may throw SqlException, but I have always assumed that it is safe to ignore any such exceptions (and I have never seen code that does not ignore them). Normally I would write: try{ connection.close(); }catch(Exception e) {} Or try{ connection.close(); }catch(Exception e) { logger.log(e.getMessage(), e); } The question is: Is it bad practice (and has anyone had problems when ignoring such exeptions). When Connection.close() does throw any exception. If it is bad how should I handle the exception. Comment: I know that discarding exceptions is evil, but I'm reffering only to exceptions thrown when closing a connection (and as I've seen this is fairly common in this case). Does anyone know when Connection.close() may throw anything?

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  • Dijkstra's Algorithm explanation java

    - by alchemey89
    Hi, I have found an implementation for dijkstras algorithm on the internet and was wondering if someone could help me understand how the code works. Many thanks private int nr_points=0; private int[][]Cost; private int []mask; private void dijkstraTSP() { if(nr_points==0)return; //algorithm=new String("Dijkstra"); nod1=new Vector(); nod2=new Vector(); weight=new Vector(); mask=new int[nr_points]; //initialise mask with zeros (mask[x]=1 means the vertex is marked as used) for(int i=0;i<nr_points;i++)mask[i]=0; //Dijkstra: int []dd=new int[nr_points]; int []pre=new int[nr_points]; int []path=new int[nr_points+1]; int init_vert=0,pos_in_path=0,new_vert=0; //initialise the vectors for(int i=0;i<nr_points;i++) { dd[i]=Cost[init_vert][i]; pre[i]=init_vert; path[i]=-1; } pre[init_vert]=0; path[0]=init_vert; pos_in_path++; mask[init_vert]=1; for(int k=0;k<nr_points-1;k++) { //find min. cost in dd for(int j=0;j<nr_points;j++) if(dd[j]!=0 && mask[j]==0){new_vert=j; break;} for(int j=0;j<nr_points;j++) if(dd[j]<dd[new_vert] && mask[j]==0 && dd[j]!=0)new_vert=j; mask[new_vert]=1; path[pos_in_path]=new_vert; pos_in_path++; for(int j=0;j<nr_points;j++) { if(mask[j]==0) { if(dd[j]>dd[new_vert]+Cost[new_vert][j]) { dd[j]=dd[new_vert]+Cost[new_vert][j]; } } } } //Close the cycle path[nr_points]=init_vert; //Save the solution in 3 vectors (for graphical purposes) for(int i=0;i<nr_points;i++) { nod1.addElement(path[i]); nod2.addElement(path[i+1]); weight.addElement(Cost[path[i]][path[i+1]]); } }

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  • Java Concurrency : Volatile vs final in "cascaded" variables?

    - by Tom
    Hello Experts, is final Map<Integer,Map<String,Integer>> status = new ConcurrentHashMap<Integer, Map<String,Integer>>(); Map<Integer,Map<String,Integer>> statusInner = new ConcurrentHashMap<Integer, Map<String,Integer>>(); status.put(key,statusInner); the same as volatile Map<Integer,Map<String,Integer>> status = new ConcurrentHashMap<Integer, Map<String,Integer>>(); Map<Integer,Map<String,Integer>> statusInner = new ConcurrentHashMap<Integer, Map<String,Integer>>(); status.put(key,statusInner); in case the inner Map is accessed by different Threads? or is even something like this required: volatile Map<Integer,Map<String,Integer>> status = new ConcurrentHashMap<Integer, Map<String,Integer>>(); volatile Map<Integer,Map<String,Integer>> statusInner = new ConcurrentHashMap<Integer, Map<String,Integer>>(); status.put(key,statusInner); In case the it is NOT a "cascaded" map, final and volatile have in the end the same effect of making shure that all threads see always the correct contents of the Map... But what happens if the Map iteself contains a map, as in the example... How do I make shure that the inner Map is correctly "Memory barriered"? Tanks! Tom

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  • Override Java System.currentTimeMillis

    - by Mike Clark
    Is there a way, either in code or with JVM arguments, to override the current time, as presented via System.currentTimeMillis, other than manually changing the system clock on the host machine? A little background: We have a system that runs a number of accounting jobs that revolve much of their logic around the current date (ie 1st of the month, 1st of the year, etc) Unfortunately, a lot of the legacy code calls functions such as new Date() or Calendar.getInstance(), both of which eventually call down to System.currentTimeMillis. For testing purposes, right now, we are stuck with manually updating the system clock to manipulate what time and date the code thinks that the test is being run. So my question is: Is there a way to override what is returned by System.currentTimeMillis? For example, to tell the JVM to automatically add or subtract some offset before returning from that method? Thanks in advance!

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  • Cast element in Java For Each statement

    - by Carl Summers
    Is it possible (or even advisable) to cast the element retrieved from a for each statement in the statement itself? I do know that each element in list will be of type . I.E.: List<BaseType> list = DAO.getList(); for(<SubType> element : list){ // Cannot convert from element type <BaseType> to <SubType> ... } rather than: List <BaseType> list = DAO.getList(); for(<BaseType> el : list){ <SubType> element = (<SubType>)el; ... }

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  • Quickest way to write to file in java

    - by user1097772
    I'm writing an application which compares directory structure. First I wrote an application which writes gets info about files - one line about each file or directory. My soulution is: calling method toFile Static PrintWriter pw = new PrintWriter(new BufferedWriter( new FileWriter("DirStructure.dlis")), true); String line; // info about file or directory public void toFile(String line) { pw.println(line); } and of course pw.close(), at the end. My question is, can I do it quicker? What is the quickest way? Edit: quickest way = quickest writing in the file

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