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  • How do I ensure my abstract class's function can only operate on extenders of the same type as the c

    - by incrediman
    For example, let's say this is my abstract class: abstract class A{ int x; int y; void foo(A fooMe); } ...and B and C are two classes which extend A. What I want is for B to only be able to call foo() on other Bs, and for C to only be able to call foo() on other Cs. But I want this to be out of the hands of the programmer who's extending my A class - that is, I want a way to ensure this functionality within As code alone. What can I do? (If possible) I'd like to avoid any hack or generics solution that's too messy - I still want foo to be able to be called like this, for example: B b=new B(); B bb=new B(); bb.foo(b);

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  • Why the generated key size is not constant?

    - by Tom Brito
    The following code prints randomly 634, 635, 636, each time I run it. Why its not constant? public static void main(String[] args) throws Exception { KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA", "BC"); keyPairGen.initialize(1024); RsaKeyPair keyPair = new RsaKeyPair(keyPairGen.generateKeyPair()); System.out.println(keyPair.getPrivate().getEncoded().length); }

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  • does anyone see any issues with this thread pattern?

    - by prmatta
    Here is a simple thread pattern that I use when writing a class that needs just one thread, and needs to a specific task. The usual requirements for such a class are that it should be startable, stopable and restartable. Does anyone see any issues with this pattern that I use? public class MyThread implements Runnable { private boolean _exit = false; private Thread _thread = null; public void start () { if (_thread == null) { _thread = new Thread(this, "MyThread"); _thread.start(); } } public void run () { while (_exit) { //do something } } public void stop () { _exit = true; if (_thread != null) { _thread.interrupt(); _thread = null; } } } I am looking for comments around if I am missing something, or if there is a better way to write this.

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  • troubles reading other apps config files

    - by Aivlis
    Hi guys, I have a problem. I have to access to the data folder of other applications from my application to read configuration's file and so on but it seems it's possible only to read data from the sdcard and my application's data folder. Can you suggest me how to solve this problem?

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  • Maven + Tomcat acceleration

    - by Bar
    I am writing a web application with Maven in the Eclipse IDE, and use Tomcat servlet container. So, I run Maven like this: mvn clean compile. It is reasonable that after this oepration I must re-run Tomcat so it can reinitialize the context (Sysdeo Tomcat launcher helps a lot). The problem is Maven execution and subsequebt Tomcat re-running takes noticable amount of time (like 10+ seconds for Maven and 20+ sec. for Tomcat, because of logging, Hibernate mappings, etc.) every time I do it. Is there any automated and more faster solution for these two operatioins? As I see it, a way better solution can be moving re-compiled classes only to the target dir.

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  • Trouble deciding return type of a method that returns a SortedSet

    - by devoured elysium
    I am supposed to make a class that should be a container for an interval of values (like in mathematics). I have already decided that I'll use internally a SortedSet. One of the the things I'm supposed to implement is a method that "gets an ordered set with all the elements in the interval". class Interval { private SortedSet sortedSet = new something(); ... <<method that should return an ordered set of values>> } My question resides in what should be both the method's return type and name. Several hypothesis arise: SortedSet getSortedElements(); I am internally using a SortedSet, so I should return that type. I should state that intent in the method's name. SortedSet getElements(); I am internally using a SortedSet, but there's no point in stating that in the method name(I don't see a big point in this one). Set getElements(); I should try to always return the most basic type, thus I am returning a Set. By the contract and definition of the method, people already know all the elements are in order. Set getSortedElements(); For the method return type, the same as above. About the method name, you are stating clearly what this method is going to return: a set of elements that are sorted. I'm inclined to use 4. , but the others also seem alright. Is there a clear winner? Why?

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  • String.split() - matching leading empty String prior to first delimiter?

    - by tehblanx
    I need to be able to split an input String by commas, semi-colons or white-space (or a mix of the three). I would also like to treat multiple consecutive delimiters in the input as a single delimiter. Here's what I have so far: String regex = "[,;\\s]+"; return input.split(regex); This works, except for when the input string starts with one of the delimiter characters, in which case the first element of the result array is an empty String. I do not want my result to have empty Strings, so that something like, ",,,,ZERO; , ;;ONE ,TWO;," returns just a three element array containing the capitalized Strings. Is there a better way to do this than stripping out any leading characters that match my reg-ex prior to invoking String.split? Thanks in advance!

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  • Synchronize JTextFields Values by PropertyChangeListener

    - by gt_ebuddy
    I want to copy the value of a jTextField - TXTFLD1 to another jTextField -TXTFLD2 when the value at TXTFLD1 changes. I choose propertychangelistener because i cannot detect when the value at TXTFLD1 is changed, Because it is changed by some external code which i cannot modify now. The test code is as follows : public class TxtFldSync extends JFrame { private JButton BTN1 = null; private JTextField TXTFLD1 = null; private JTextField TXTFLD2 = null; public static void main(String[] args) { TxtFldSync thisClass = new TxtFldSync(); thisClass.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); thisClass.setVisible(true); } public TxtFldSync() { super(); this.setSize(300, 200); BTN1 = new JButton(); BTN1.setBounds(new Rectangle(178, 38, 67, 17)); TXTFLD1 = new JTextField(); TXTFLD1.setBounds(new Rectangle(32, 42, 83, 20)); TXTFLD2 = new JTextField(); TXTFLD2.setBounds(new Rectangle(30, 78, 83, 20)); //listeners TXTFLD1.addPropertyChangeListener("value", new PropertyChangeListener() { @Override public void propertyChange(PropertyChangeEvent arg0) { TXTFLD2.setText(TXTFLD1.getText()+"set by change listener"); //this doesnot work why ? } }); BTN1.addActionListener( new ActionListener() { @Override public void actionPerformed(ActionEvent arg0) { TXTFLD1.setText("Action Performed"); //i what to set same value to TXTFLD2 using property change listener } }); this.setContentPane(new Container()); this.getContentPane().add(BTN1); this.getContentPane().add(TXTFLD1); this.getContentPane().add(TXTFLD2); } } Why the property change listener is not working. What are the other alternatives solution for this problem?

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  • proper way to use list to array?

    - by cometta
    public class TestClass{ private String divisions[] ={}; public void doAction(){ Collection testArray = new ArrayList(); // put testArray will data divisions = (String [] ) testArray.toArray(division); //should i use this divisions = (String [] ) testArray.toArray(new String [] {}); //should i use this? } } if i use case 1, and i call doaction multiple time, the division, something will show wrong records if i use case2, divisions will always show the correct records. is my assumption should use case 2?

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  • Android app using 2.x APIs that will also run on 1.x

    - by Adam Haile
    I'm working on an Android app in which I would like to use multi-touch. However, I do not want to completely leave out those still running a 1.x OS phone. How do you program the app so that you can use the 2.x multi-touch APIs (or any other higher level API for that matter) and still allow it to gracefully degrade on 1.x systems. If you create a project in Eclipse for 1.x can you even still access the 2.x APIs? Basically I want it to show up in the marketplace and work on all 1.6 and higher phones and just allow access to the higher level functionality if available. Also, if anyone can point me to any data on the number of 1.x devices vs. 2.x devices in use, it would be greatly appreciated.

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  • In web project can we write core services layer without knowledge of UI ?

    - by Silent Warrior
    I am working on web project. We are using flex as UI layer. My question is often we are writing core service layer separately from web/UI layer so we can reuse same services for different UI layer/technology. So practically is it possible to reuse same core layer services without any changes/addition in API with different kind of UI technologies/layers. For e.g. same core service layer with UI technology which supports synchronized request response (e.g. jsp etc.) and non synchronize or event driven UI technology (e.g Ajax, Flex, GWT etc.) or with multiple devices like (computers, mobiles, pdas etc.). Personally I feel its very tough to write core service layer without any knowledge of UI. Looking for thoughts from other people.

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  • What is "Android Activity", what is the difference between "BlankActivity", and "MasterDetailFlow"?

    - by Adrianus Hendry
    I want to create an android application using Eclipse Juno, but then i am getting confused of what the "activity" actually is. The first time i created android app project, there was an option that require me to select whether i want to create activity, and if so, i need to choose between BlankActivity and MasterDetailFlow. Also, is it possible that an application has many activities? I think i need some tutorials about creating android application using eclipse, so if you have a good tuts either it is in text or videos i will appreciate it. Actually i am a newbie in mobile apps development, so i wish the answer will be less complex. Thanks in advance.

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  • I asked a question about arrays before, but this one won't compile

    - by unit
    I asked about this array a little while ago, and I can't see what the problem is. Too tired. What have I done wrong? Basically, I am taking a string array and trying to check to see if it contains numbers or an x (ISBN number validation). I want to take the number from a given input (bookNum), check the input, and feed any valid input into a new array (book). At the line 'bookNum.charAt[j]==book[i]' I get the 'not a statement error'. What gives? String[] book = new String [ISBN_NUM]; bookNum.replaceAll("-",""); if (bookNum.length()!=ISBN_NUM) throw new ISBNException ("ISBN "+ bookNum + " must be 10 characters"); for (int i=0;i<bookNum.length();i++) { if (Character.isDigit(bookNum.charAt(i))) bookNum.CharAt[j]==book[i]; j++; if (book[9].isNotDigit()|| book[9]!="x" || book[9]!="X") throw new ISBNException ("ISBN " + bookNum + " must contain all digits" + "or 'X' in the last position");

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  • MySQL Connection Error with JSP

    - by voidmain
    Hello, I am trying to connect to mysql database from jsp page. The connection code is as below InitialContext ic=new InitialContext(); DataSource ds=(DataSource)ic.lookup("jdbc:mysql://localhost:3306/"); Connection con=ds.getConnection(); Statement stmt = con.createStatement(); when i open the page i get the following error javax.servlet.ServletException: javax.naming.NamingException: Lookup failed for 'jdbc:mysql://localhost:3306/' in SerialContext [Root exception is javax.naming.NameNotFoundException: jdbc:mysql:] can some one please tell me what is wrong with this...

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  • Android - Access to online Database SQlite

    - by Oneiros
    I need to open, read and insert items into an online SQLite database from an Android app. I know url, username and password. In JavaSE i would do the following: Class.forName("com.mysql.jdbc.Driver"); Connection dbConnection = DriverManager.getConnection(URL, USER, PASSWORD); I read that I can't do this in Android because there is not a JDBC Driver (there is a "SQLite.JDBCDriver" but it is not documented and not recommended). So which is the easiest way? I asked to Google but it looks like he either doesn't know.

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  • new JDK 7 features

    - by xdevel2000
    I wish to test the new features that will came with the next JDK like project coin, project lambda etc. but the last JDK 7 to download will not have any already implemented! From which build can I test them? I think it's incredible that, now in may 2010 at few months to the official final release (november 2010????) for we developers there is no possibility to test any of this features!!

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  • Polymorphic behavior not being implemented

    - by Garrett A. Hughes
    The last two lines of this code illustrate the problem: the compiler works when I use the reference to the object, but not when I assign the reference to an array element. The rest of the code is in the same package in separate files. BioStudent and ChemStudent are separate classes, as well as Student. package pkgPoly; public class Poly { public static void main(String[] arg) { Student[] stud = new Student[3]; // create a biology student BioStudent s1 = new BioStudent("Tom"); // create a chemistry student ChemStudent s2 = new ChemStudent("Dick"); // fill the student body with studs stud[0] = s0; stud[1] = s1; // compiler complains that it can't find symbol getMajor on next line System.out.println("major: " + stud[0].getMajor() ); // doesn't compile; System.out.println("major: " + s0.getMajor() ); // works: compiles and runs correctly } }

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  • Hibernate reverse engineering

    - by EugeneP
    I have a structure where the main table is USER, other tables include CATEGORY (contains user_id). What I got after the standard reverse engineering procedure was: the class User contained a collection of categories, the class Category didn't contain the foreign key (user_id) but it did contain the User object. Why did it not contain the foreign key as a class property? And how do I join these two tables in HQL without that glue? HQL - please explain this part.

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  • Can I have a set containing identical elements?

    - by Roman
    It is convenient for me to use a set. I like how I can "add" ("remove") an element to (from) the set. It is also convenient to check if a given element is in the set. The only problem, I found out that I cannot add a new element to a set if the set has already such an element. Is it possible to have "sets" which can contain several identical elements.

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  • Will this be garbage collected in JVM?

    - by stjowa
    I am running the following code every two minutes via a Timer: object = new Object(this); Potentially, this is a lot of objects being created and a lot of objects being overwritten. Do the overwritten objects get garbage collected, even with a reference to itself being used in the newly created object? I am using JDK 1.6.0_13. Thanks for the help.

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  • Backing Bean not getting values sent by javascript

    - by Developer106
    I have three drop down lists whose values are been copied to <h:inputHidden> components by the following JavaScript function: function getBirthDate() { var months = document.getElementById("months") var hidden1 = document.getElementById("formsignup:monthField"); hidden1.value = months.options[months.selectedIndex].text; var days = document.getElementById("days"); var hidden2 = document.getElementById("formsignup:dayField"); hidden2.value = days.options[days.selectedIndex].value; var years = document.getElementById("years"); var hidden3 = document.getElementById("formsignup:yearField"); hidden3.value = years.options[years.selectedIndex].value; } Here are the three <h:inputHidden> components: <h:inputHidden value="#{signupBean.month}" id="monthField"/> <h:inputHidden value="#{signupBean.day}" id="dayField"/> <h:inputHidden value="#{signupBean.year}" id="yearField"/> This is the command button that is supposed to invoke the function that copies the values to the inputs and then submits them to the backing bean. <h:commandButton image="images/images/signup1.png" styleClass="joinnow" id="joinus" action="#{signupBean.save}" onclick="getBirthDate()" /> But they arrive as null in the backing bean. How is this caused and how can I solve it?

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  • JFileChooser select directory but show files

    - by Jeff Storey
    I feel like there should be a simple way to do this but I can't figure it out. I have a JFileChooser that allows the user to select directories. I want to show all the files in the directories to give the user some context, but only directories should be accepted as selections (maybe the Open button would be disabled when a file is selected). Is there an easy way of doing this?

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