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  • Java: why does extending need an empty constructor?

    - by HH
    I have classes SearchToUser and getFilesToWord. GetFilesToWord must inherit SearchToUser fields. Extending works if an empty construction in SearchToUser-class, otherwise: cannot find symbol symbol : constructor SearchToUser() location: class SearchToUser public class GetFilesToWord extends SearchToUser{ ^ 1 error make: *** [all] Error 1 I cannot understand why the empty constructor is required for extending.

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  • How to make prevent public key inside jar to be saved using Java code

    - by Abhijith V R
    After signing a jar , we can retrieve the public keys from jar using Certificate[] cert = jarentry.getCertificates(); Once certificate is extracted we can save this to a new keystore as trusted cert. Once this is done , then second user can sign any jar using this certificate , isn't ? I want to distribute content as jars , contents will contain properties files for a application init. I want to make sure that an user is not capable to rebuilding the property files using the certificate he extracted from jarentry. In the code which reads the jar contents i am checking that jar is signed with my certificate only and also checking that jar is not tampered with . But the issue came to my mind that if i am able to extract the cerificate from jar then why don;t a third guy ? Can any one help me in this............

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  • Java resource closing

    - by Bob
    Hi, I'm writing an app that connect to a website and read one line from it. I do it like this: try{ URLConnection connection = new URL("www.example.com").openConnection(); BufferedReader rd = new BufferedReader(new InputStreamReader(connection.getInputStream())); String response = rd.readLine(); rd.close(); }catch (Exception e) { //exception handling } Is it good? I mean, I close the BufferedReader in the last line, but I do not close the InputStreamReader. Should I create a standalone InputStreamReader from the connection.getInputStream, and a BufferedReader from the standalone InputStreamReader, than close all the two readers? I think it will be better to place the closing methods in the finally block like this: InputStreamReader isr = null; BufferedReader br = null; try{ URLConnection connection = new URL("www.example.com").openConnection(); isr = new InputStreamReader(connection.getInputStream()); br = new BufferedReader(isr); String response = br.readLine(); }catch (Exception e) { //exception handling }finally{ br.close(); isr.close(); } But it is ugly, because the closing methods can throw exception, so I have to handle or throw it. Which solution is better? Or what would be the best solution?

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  • To instantiate BiMap Of google-collections in Java

    - by Masi
    How can you instantiate a Bimap of Google-collections? I know the thread. A sample of my code import com.google.common.collect.BiMap; public class UserSettings { private Map<String, Integer> wordToWordID; UserSettings() { this.wordToWordID = new BiMap<String. Integer>(); I get cannot instantiate the type BiMap<String, Integer>.

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  • Adding Listeners at runtime? - Java MVC

    - by Halo
    My model in my MVC pattern, generates components at runtime and gives them to the View to be displayed on the screen through update() method (you know, model is the observable and the view is the observer). But I also need to add listeners to these components, and the controller has the listener methods (because they say the MVC pattern is like this) and it's not involved in this update process. So I can't add the listeners at runtime, but only in the controller's constructor at startup. I've got an idea, that is making the controller the observer and then giving the data to the view, as well as adding the listeners. Do you think this would be OK?

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  • java regular expression

    - by changed
    Hi I have to create a regular expression for some path conversion. Example for path are //name:value /name:value // name:value /name:value /name:value /name:value//name:value thing is how to check for // or / at the start or middle of the string and how can i specify that name can contain any of this a-zA-Z and _ Path also contains white spaces. thanks-

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  • What's "@Override" there for in java?

    - by symfony
    public class Animal { public void eat() { System.out.println("I eat like a generic Animal."); } } public class Wolf extends Animal { @Override public void eat() { System.out.println("I eat like a wolf!"); } } Does @Override actually have some functionality or it's just kinda comment?

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  • J2EE fast track (Learning Enterprise Java real fast)

    - by IndexController
    Hello, We just started a new project in J2EE in our office and i am required to participate effectively. I mostly work on web applications and I use PHP/MySql but I also know J2SE and have written couple of standalone applications. I need help and advise on how i can learn J2ee very fast so that i can blend into the project without difficulties. I need help with book & tutorial recommendations and also links to resources. Thank you for your time.

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  • Java Generic Casting Type Mismatch

    - by Kay
    public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; public void main(String[] args){ int i; T[] arr = {1,3,4,5,2}; //ERROR HERE ******* foo } public T[] Heapsort(T[]anArray, int n){ // build initial heap T[]sortedArray = anArray; for (int i = n-1; i< 0; i--){ //assert: the tree rooted at index is a semiheap heapRebuild(anArray, i, n); //assert: the tree rooted at index is a heap } //sort the heap array int last = n-1; //invariant: Array[0..last] is a heap, //Array[last+1..n-1] is sorted for (int j=1; j<n-1;j++) { sortedArray[0]=sortedArray[last]; last--; heapRebuild(anArray, 0, last); } return sortedArray; } protected void heapRebuild(T[ ] items, int root, int size){ foo } } The error is on the line with "T[arr] = {1,3,4,5,2}" Eclispe complains that there is a: "Type mismatch: cannot convert from int to T" I've tried to casting nearly everywhere but to no avail.A simple way out would be to not use generics but instead just ints but that's sadly not an option. I've got to find a way to resolve the array of ints "{1,3,4,5,2}" into an array of T so that the rest of my code will work smoothly.

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  • Human readable and parsable date format in Java.

    - by Savvas Dalkitsis
    I want to save a Date object to a readable string (for example 22/10/2009 21:13:14) that is also parsable back to a Date object. I have tried many things and the best I could find was to use DateFormater for parsing and formating but it has a setback. When you format a date you lose seconds information. I tried to find if there is an option to format it and display the seconds (even better would be to the millisecond level since that's the resolution the Date object allows you to have) but I came up short. Any ideas?

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  • Symbol error in java application using netbeans when adding a shared project to library

    - by Malachi
    I have a project which has shared functionality between three other projects and have linked these to existing projects as I normally would using the add project functionality of the libraries folder. This all used to work however when I started up Netbeans yesterday it just wasn't working as in the other projects won't compile even though the projects are linked. It can recognise the packages - just the actual classes themselves were not recognised... and to add to the weirdness some of the classes are getting picked up fine. I have checked the dist folder of the shared project and the Shared.jar file exists. Also I have checked the Jar and the other classes that are not being recognises are there also. Any suggestions?

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  • Java - Custom PropertyEditorSupport to display units

    - by I82Much
    All, I'm trying to make the properties of my node have Units associated with the measure. ( I am using the JScience.org implementation of JSR 275) So for instance, public class Robot extends AbstractNode { // in kg float vehicleMass; @Override public Sheet createSheet() { Sheet s = Sheet.createDefault(); Sheet.Set set = s.createPropertiesSet(); try { PropertySupport.Reflection vehicleMassField = new PropertySupport.Reflection(this, float.class, "vehicleMass"); vehicleMassField.setValue("units", SI.KILOGRAMS); vehicleMassField.setName("vehicleMass"); set.put(vehicleMassField); PropertyEditorManager.registerEditor(float.class, UnitInPlaceEditor.class); } catch (NoSuchMethodException ex) { Exceptions.printStackTrace(ex); } s.put(set); return s; } } I want my UnitInPlaceEditor to append the units to the end of the string representation of the number, and when the field is clicked (enters edit mode) for the units to disappear and just the number becomes selected for editing. I can make the units appear, but I cannot get the units to disappear when the field enters editing mode. public class UnitsInplaceEditor extends PropertyEditorSupport implements ExPropertyEditor { private PropertyEnv pe; @Override public String getAsText() { // Append the unit by retrieving the stored value } @Override public void setAsText(String s) { // strip off the unit, parse out the number } public void attachEnv(PropertyEnv pe) { this.pe = pe; } } Here's a screenshot of the display - I like it like this.. but here's the value being edited; note the unit stays there. Basically I want one value (string) to be displayed in the field when the field is NOT being edited, and a different to be displayed when user starts editing the field. Barring that, I'd like to put a constant jlabel for the units (uneditable) to the right of the text field. Anyone know how to do this?

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  • Creating java class with annotated fields in runtime

    - by Sarmun
    The problem is that I need to create in runtime a class like this: public class Foo { @Bar int value0; @Bar int value1; @Bar int value2; .... } with number of fields being decided at runtime. I was looking at Javassist, and there you can create a new class, and add fields to it, but I haven't found a way to annotate those fields.

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  • What is faster- Java or C# (Or good old C)?

    - by Rexsung
    I'm currently deciding on a platform to build a scientific computational product on, and am deciding on either C#, Java, or plain C with Intels compiler on Core2 Quad CPU's. It's mostly integer arithmetic. My benchmarks so far show Java and C are about on par with each other, and dotNET/C# trails by about 5%- however a number of my coworkers are claiming that dotNET with the right optimizations will beat both of these given enough time for the JIT to do its work. I always assume that the JIT would have done it's job within a few minutes of the app starting (Probably a few seconds in my case, as it's mostly tight loops), so I'm not sure whether to believe them Can anyone shed any light on the situation? Would dotNET beat Java? (Or am I best just sticking with C at this point?). The code is highly multithreaded and data sets are several terabytes in size. Haskell/erlang etc are not options in this case as there is a significant quantity of existing legacy C code that will be ported to the new system, and porting C to Java/C# is a lot simpler than to Haskell or Erlang. (Unless of course these provide a significant speedup). Edit: We are considering moving to C# or Java because they may, in theory, be faster. Every percent we can shave off our processing time saves us tens of thousands of dollars per year. At this point we are just trying to evaluate whether C, Java, or c# would be faster.

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  • java casting confusion

    - by Stardust
    Could anyone please tell me why the following casting is resulting in compile time error: Long l = (Long)Math.pow(5,2); But why not the following: long l = (long)Math.pow(5,2);

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  • [java] Trying to use ResourceBundle to fetch messages from external file

    - by bumperbox
    Essentially I would like to have a messages.properties files external to the jar files in my application. So that users can add languages and edit the files easily if my translations are wrong at the moment i use ResourceBundle.getBundle("package.MessageBundle"); But i would like to do something like this ResourceBundle.getBundle("lang/MessageBundle"); Where lang is a folder under my application installation directory. is this a good idea (if not, why not)? can someone point me in the right direction, or some sample code that does this thanks Alex

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  • Java RandomAccessFile - dealing with different newline styles?

    - by waitinforatrain
    Hey, I'm trying to seek through a RandomAccessFile, and as part of an algorithm I have to read a line, and then seek backwards from the end of the line E.g String line = raf.readLine(); raf.seek (raf.getFilePointer() - line.length() + m.start() + m.group().length()); //m is a Matcher for regular expressions I've been getting loads of off-by-one errors and couldn't figure out why. I just discovered it's because some files I'm reading from have UNIX-style linefeeds, \r\n, and some have just windows-style \n. Is there an easy to have the RandomAccessFile treat all linefeeds as windows-style linefeeds?

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  • Java: Match tokens between two strings and return the number of matched tokens

    - by Cryssie
    Need some help to find the number of matched tokens between two strings. I have a list of string stored in ArrayList (example given below): Line 0 : WRB VBD NN VB IN CC RB VBP NNP Line 1 : WDT NNS VBD DT NN NNP NNP Line 2 : WRB MD PRP VB DT NN IN NNS POS JJ NNS Line 3 : WDT NN VBZ DT NN IN DT JJ NN IN DT NNP Line 4 : WP VBZ DT JJ NN IN NN Here, you can see each string consists of a bunch of tokens separated by spaces. So, there's three things I need to work with.. Compare the first token (WRB) in Line 0 to the tokens in Line 1 to see if they match. Move on to the next tokens in Line 0 until a match is found. If there's a match, mark the matched tokens in Line 1 so that it will not be matched again. Return the number of matched tokens between Line 0 and Line 1. Return the distance of the matched tokens. Example: token NN is found on position 3 on line 0 and position 5 on Line 1. Distance = |3-5| = 2 I've tried using split string and store it to String[] but String[] is fixed and doesn't allow shrinking or adding of new elements. Tried Pattern Matcher but with disasterous results. Tried a few other methods but there's some problems with my nested for loops..(will post part of my coding if it will help). Any advice or pointers on how to solve this problem this would be very much appreciated. Thank you very much.

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