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  • interface as a method parameter in Java

    - by PeterYu
    Hi all, I had an interview days ago and was thrown a question like this. Q: Reverse a linked list. Following code is given: public class ReverseList { interface NodeList { int getItem(); NodeList nextNode(); } void reverse(NodeList node) { } public static void main(String[] args) { } } I was confused because I did not know an interface object could be used as a method parameter. The interviewer explained a little bit but I am still not sure about this. Could somebody enlighten me?

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  • Java - JPA - @Version annotation

    - by Yatendra Goel
    I am new to JPA. I am cofused about the @Version annotation. How it works? I have googled it and found various answers whose extract is as follows: JPA uses a version field in your entities to detect concurrent modifications to the same datastore record. When the JPA runtime detects an attempt to concurrently modify the same record, it throws an exception to the transaction attempting to commit last. But still I am not sure how it works? ================================================================================== Also as from the following lines: You should consider version fields immutable. Changing the field value has undefined results. Does it mean that we should declare our version field as final

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  • java overloaded method

    - by Sean Nguyen
    Hi, I have an abstract template method: class abstract MyTemplate { public void something(Object obj) { doSomething(obj) } protected void doSomething(Object obj); } class MyImpl extends MyTemplate { protected void doSomething(Object obj) { System.out.println("i am dealing with generic object"); } protected void doSomething(String str) { System.out.println("I am dealing with string"); } } public static void main(String[] args) { MyImpl impl = new MyImpl(); impl.something("abc"); // --> this return "i am dealing with generic object" } How can I print "I am dealing with string" w/o using instanceof in doSomething(Object obj)? Thanks,

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  • StringBufferInputStream Question in Java

    - by JJG
    I want to read an input string and return it as a UTF8 encoded string. SO I found an example on the Oracle/Sun website that used FileInputStream. I didn't want to read a file, but a string, so I changed it to StringBufferInputStream and used the code below. The method parameter jtext, is some Japanese text. Actually this method works great. The question is about the deprecated code. I had to put @SuppressWarnings because StringBufferInputStream is deprecated. I want to know is there a better way to get a string input stream? Is it ok just to leave it as is? I've spent so long trying to fix this problem that I don't want to change anything now I seem to have cracked it. @SuppressWarnings("deprecation") private String readInput(String jtext) { StringBuffer buffer = new StringBuffer(); try { StringBufferInputStream sbis = new StringBufferInputStream (jtext); InputStreamReader isr = new InputStreamReader(sbis, "UTF8"); Reader in = new BufferedReader(isr); int ch; while ((ch = in.read()) > -1) { buffer.append((char)ch); } in.close(); return buffer.toString(); } catch (IOException e) { e.printStackTrace(); return null; } }

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  • java: how to parse html-like xml

    - by Yang
    I have an html-like xml, basically it is html. I need to get the elements in each . Each element looks like this: <line tid="744476117"> <attr>1414</attr> <attr>31</attr><attr class="thread_title">title1</attr><attr>author1</attr><attr>date1</attr></line> My code is as below, it does recognize that there are 50 in the file, but it gives me NULLPointException when parsing NodeList fstNmElmntLst = fstElmnt.getElementsByTagName("attr"); Any idea why this is happening? The same code has been used for other applications without problems. DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); InputSource is = new InputSource(); is.setCharacterStream(new StringReader(cleanxml)); Document doc = db.parse(is); doc.getDocumentElement().normalize(); System.out.println("Root element " + doc.getDocumentElement().getNodeName()); NodeList nodeLst = doc.getElementsByTagName("line"); for (int s = 0; s < nodeLst.getLength(); s++) { System.out.println(nodeLst.getLength()); Node fstNode = nodeLst.item(s); if (fstNode.getNodeType() == Node.ELEMENT_NODE) { Element fstElmnt = (Element) fstNode; NodeList fstNmElmntLst = fstElmnt.getElementsByTagName("attr"); Element fstNmElmnt = (Element) fstNmElmntLst.item(0); NodeList fstNm = fstNmElmnt.getChildNodes(); System.out.println("attr : " + ((Node) fstNm.item(0)).getNodeValue()); } }

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  • Java/Android get array from xml

    - by Ashley
    I have a list of longitude and longitude points in an xml file that is used throughout my application. I find my self repeating this code to get points often and think there must be a better way? String[] mTempArray = getResources().getStringArray(R.array.stations); int len = mTempArray.length; mStationArray = new ArrayList<Station>(); for(int i = 0; i < len; i++){ Station s = new Station(); String[] fields = mTempArray[i].split("[\t ]"); s.setValuesFromArray(fields); Log.i("ADD STATION", ""+s); mStationArray.add(s); } XML is in the format of: <?xml version="1.0" encoding="utf-8"?> <resources> <array name="stations"> <item> <name>Station name</name> <longitude>1111111</longitude> <latitude>11111</latitude> <code>1</code> </item> And another (possible) problem is that to get just one station I have to get all of them and pull the one I want from the array. Is this going to be considerably slower? Can I make this array consistent throughout the app? (But keeping the separate Intent methodology)

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  • Output Parameter in java

    - by soclose
    Hi, could u give me a sample code of using output parameter in function? I tried to google it but just found it in function. I'd like to use this output value in another function. I will use this code in Android.

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  • How do I alias the scala setter method 'myvar_$eq(myval)' to something more pleasing when in java?

    - by feydr
    I've been converting some code from java to scala lately trying to teach myself the language. Suppose we have this scala class: class Person() { var name:String = "joebob" } Now I want to access it from java so I can't use dot-notation like I would if I was in scala. So I can get my var's contents by issuing: person = Person.new(); System.out.println(person.name()); and set it via: person = Person.new(); person.name_$eq("sallysue"); System.out.println(person.name()); This holds true cause our Person Class looks like this in javap: Compiled from "Person.scala" public class Person extends java.lang.Object implements scala.ScalaObject{ public Person(); public void name_$eq(java.lang.String); public java.lang.String name(); public int $tag() throws java.rmi.RemoteException; } Yes, I could write my own getters/setters but I hate filling classes up with that and it doesn't make a ton of sense considering I already have them -- I just want to alias the _$eq method better. (This actually gets worse when you are dealing with stuff like antlr because then you have to escape it and it ends up looking like person.name_\$eq("newname"); Note: I'd much rather have to put up with this rather than fill my classes with more setter methods. So what would you do in this situation?

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  • What are the alternatives for Java authentication?

    - by Crusader
    Preferably something that integrates well with a Flex front end. Yes the Spring Security guys say this is possible, but all examples seem to use legacy jsp tag libraries making them half useless as examples. I don't want to spend a month setting up and learning how to use a security tool. I would like a tool which supports using annotations (@RolesAllowed etc), MINIMAL XML, and 'remember-me' features (not cookie based). Apache Shiro seems to support Flex/Silverlight/Swing as well but I'd like to know if there are any other alternatives that are NOT container specific.

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  • How does file creation work in Java

    - by Ankur
    I am trying to create a file using File newFile = new File("myFile"); However no file called "myFile" is created. This is within a Web application Project i.e. proper form to be pakaged as a WAR but I am calling it as part of a main method (just to see how this works). How can I make it so that a new file is created at a location relative to the current one i.e not have to put in an absolute path.

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  • delete item from array in java

    - by davit-datuashvili
    hello can anybody tell me what is wrong here? i want delete item from array but it shows me error ArrayIndexOutBound exception public class delete{ public static void main(String[]args){ int i; //delete item from array int k[]=new int[]{77,99,44,11,00,55,66,33,10}; //delete 55 int searchkey=55; int nums=k.length; for ( i=0;i<nums;i++) if (k[i]==searchkey) break; for (int t=i;t<nums;t++) k[t]=k[t+1]; nums--; for (int m=0;m<nums;m++){ System.out.println(k[m]); } } }

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  • Java Font Display Problem

    - by Yan Cheng CHEOK
    I realize that, in my certain customer side, when I use the font provided by Graphics2D itself, and decrease the size by 1, it cannot display properly. private void drawInformationBox(Graphics2D g2, JXLayer<? extends V> layer) { if (MainFrame.getInstance().getJStockOptions().getYellowInformationBoxOption() == JStockOptions.YellowInformationBoxOption.Hide) { return; } final Font oldFont = g2.getFont(); final Font paramFont = new Font(oldFont.getFontName(), oldFont.getStyle(), oldFont.getSize()); final FontMetrics paramFontMetrics = g2.getFontMetrics(paramFont); final Font valueFont = new Font(oldFont.getFontName(), oldFont.getStyle() | Font.BOLD, oldFont.getSize() + 1); final FontMetrics valueFontMetrics = g2.getFontMetrics(valueFont); /* * This date font cannot be displayed properly. Why? */ final Font dateFont = new Font(oldFont.getFontName(), oldFont.getStyle(), oldFont.getSize() - 1); final FontMetrics dateFontMetrics = g2.getFontMetrics(dateFont); Rest of the font is OK. Here is the screen shoot (See the yellow box. There are 3 type of different font within the yellow box) :

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  • implementing keepalives with Java

    - by Bilal
    Hi All, I am biulding a client-server application where I have to implement a keepalive mechanism in order to detect that the client has crashed or not. I have separate threads on both client and server side. the client thread sends a "ping" then sleeps for 3 seconds, while the server reads the BufferedInput Stream and checks whether ping is received, if so it makes the ping counter eqauls zero, else it increments the counter by +1, the server thread then sleeps for 3 seconds, if the ping counter reaches 3, it daclares the client as dead. The problem is that when the server reads the input stream, its a blocking call, and it blocks untill the next ping is received, irrespective of how delayed it is, so the server never detects a missed ping. any suggestions, so that I can read the current value of the stream and it doesn't block if there is nothing on the incoming stream. Thanks,

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  • Using enums in Java across multiple classes

    - by Richard Mar.
    I have the following class: public class Card { public enum Suit { SPACES, HEARTS, DIAMONDS, CLUBS }; public Card(Suit nsuit, int nrank) { suit = nsuit; rank = nrank; } private Suit suit; private int rank; } I want to instantiate it in another class, but that class doesn't understand the Suit enum. Where should I put the enum to make it publicly visible?

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  • What is an Enterprise Java Bean really?

    - by HDave
    On the Tomcat FAQ it says: "Tomcat is not an EJB server. Tomcat is not a full J2EE server." But if I: use Spring to supply an application context annotate my entities with JPA annotations (and use Hibernate as a JPA provider) configure C3P0 as a connection pooling data source annotate my service methods with @Transactional (and use Atomikos as JTA provider) Use JAXB for marshalling and unmarshalling and possibly add my own JNDI capability then don't I effectively have a JEE application server? And then aren't my beans EJBs? Or is there some other defining characteristic? What is it that a JEE compliant app server gives you that you can't easily/readily get from Tomcat with some 3rd party subsystems?

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  • Issue with WatchService in java 7

    - by user972590
    I'm using jdk7's WatchService API for monitoring the folder on file system.I'm sending a new file through email to that folder, when the file comes into that folder i m triggering the ENTRY_CRATE option. its working fine. But the issue is its generating two events of ENTRY_CREATE instead of one event which i'm invoking. BELOW IS THE CODE: Path dir = Paths.get(/var/mail); WatchService watcher = dir.getFileSystem().newWatchService(); dir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE); System.out.println("waiting for new file"); WatchKey watckKey = watcher.take(); List<WatchEvent<?>> events = watckKey.pollEvents(); System.out.println(events.size()); for(WatchEvent<?> event : events){ if(event.kind() == StandardWatchEventKinds.ENTRY_CREATE){ String fileCreated=event.context().toString().trim(); } } In the above code I'm gettng the events size as 2. Can any one please help me in finding out the reason why i'm getting two events.

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  • Java, merging two arrays evenly

    - by user2435044
    What would be the best way to merge two arrays of different lengths together so they are evenly distributed in the new array? Say I have the following arrays String[] array1 = new String[7]; String[] array2 = new String[2]; String[] mergedArray = new String[array1.length + array2.length]; I would want mergedArray to have the following elements array1 array1 array1 array2 array1 array1 array1 array2 array1 but if I were to change the size of the arrays to String[] array1 = new String[5]; String[] array2 = new String[3]; String[] mergedArray = new String[array1.length + array2.length]; then I would want it to be array1 array2 array1 array2 array1 array2 array1 array1 basically if it can be helped each array2 element shouldn't be touching each other; exception if array2 has a size larger than array1.

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  • Maven easyb plugin java heap space settings?

    - by vinnu
    Hi, I attempted to change my heap size for maven easyb plugin http://www.easyb.org/maven-easyb-plugin/. In my easyb test I added standard code to print the heap size using the code Runtime.getFreeMemory() and Runtime.getTotalMemory(). I tried setting the MAVEN_OPTS=-Xmx1024m -Xms1024m and also set the maven opts in Maven surefire plugin. Now when I run the same class from the Junit I can see the getTotalMemory() displaying a number close 1Gig but the when the same classes are invoked from easyb plugin they do not reflect the memory size. Shouldn't there be a way of passing JVM opts to maven easyb plugin when it runs these easyb tests? At the very minimum it should atleast pick up the MAVEN_OPTS settings from the environment. Has someone bumped into problems like this? (A search on this group's archive does not reveal much)

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  • Java - Regex problem

    - by Yatendra Goel
    I have a list of urls of type http://www.abc.com/pk/ca and http://www.abc.com/pk Now, I want to find out only those urls that ends with /pk or /pk/ and don't have anything in between .com and /pk

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  • Java - Regex problem

    - by Yatendra Goel
    I have list of urls of types: http://www.abc.com/pk/etc http://www.abc.com/pk/etc/ http://www.abc.com/pk/etc/etc where etc can be anything. So I want to search only those urls that contains www.abc.com/pk/etc or www.abc.com/pk/etc/

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  • Singleton & Multithreading in Java

    - by vivek jagtap
    What is the preferred way to work with Singleton class in multithreaded environment? Suppose if I have 3 thread, and all they try to access getInstance() method of singleton class at the same time - What would happen if no synchronization is maintained? Is it good practice to use synchronized getInstance() method or use synchronized block inside getInstance(). Please advise if there is any other way out.

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  • Revalidate and repaint - Java Swing

    - by bosra
    I have a JPanel that I am adding JLabel's to. I then want to remove all the JLabels and add some new ones. So I do the following: panel.removeAll();panel.repaint(); panel.add(new JLabel("Add something new"); panel.revalidate(); This works fine. My problem arises when I start a new thread after this like: panel.removeAll();panel.repaint(); (1)panel.add(new JLabel("Add something new"); panel.revalidate(); //new thread to start - this thread creates new JLabels that should appear under (1) firstProducer.start(); try { firstProducer.join(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Then the output from the original JLabels is still visible. I have read that the revalidate process is a long running task and hence the firstProducer thread is getting started while the revalidation is going on and a conflict is arising. What is the best way to deal with this?

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