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  • Java generics question with wildcards

    - by Sean
    Just came across a place where I'd like to use generics and I'm not sure how to make it work the way I want. I have a method in my data layer that does a query and returns a list of objects. Here's the signature. public List getList(Class cls, Map query) This is what I'd like the calling code to look like. List<Whatever> list = getList(WhateverImpl.class, query); I'd like to make it so that I don't have to cast this to a List coming out, which leads me to this. public <T> List<T> getList(Class<T> cls, Map query) But now I have the problem that what I get out is always the concrete List<WhateverImpl> passed in whereas I'd like it to be the Whatever interface. I tried to use the super keyword but couldn't figure it out. Any generics gurus out there know how this can be done?

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  • How to access java classes in a subfolder.

    - by Jacob
    Hi all. I'm trying to make a program that can load an unknown set of plugins from a sub-folder, "Plugins". All of these plugins implement the same interface. What I need to know is how do I find all of the classes in this folder so that I can instantiate and use them?

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  • Java generic return tpye

    - by Colby77
    Hi, I'd like to write a method that can accept a type param (or whatever the method can figure out the type from) and return a value of this type so I don't have to cast the return type. Here is a method: public Object doIt(Object param){ if(param instanceof String){ return "string"; }else if(param instanceof Integer){ return 1; }else{ return null; } } When I call this method, and pass in it a String, even if I know the return type will be a String I have to cast the return Object. This is similar to the int param. How shall I write this method to accept a type param, and return this type?

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  • creating Sites using java

    - by rajalakshmi
    Hi i developed one application used to create google sites by referring the developer guide in which i don't know what are the three parameters in this is particular line SitesService client = new SitesService("yourCo-yourAppName-v1"). This is my problem. help me

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  • ontology with java(jena)

    - by Udayanga
    I'm doing some project which is based on ontology.I want to identify semantic of the text that has entered by user. Is there any possible way to fulfill my task dealing with ontology through jena?

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  • Why are these lines being skipped? (java)

    - by David
    Here's the relevant bit of the source code: class Dice { String name ; int x ; int[] sum ; ... public Dice (String name) { this.name = name ; this.x = 0 ; this.sum = new int[7] ; } ... public static void main (String[] arg) { Dice a1 = new Dice ("a1") ; printValues (a1) ; } public static void printDice (Dice Dice) { System.out.println (Dice.name) ; System.out.println ("value: "+Dice.x) ; printValues (Dice) ; } public static void printValues (Dice Dice) { for (int i = 0; i<Dice.sum.length; i++) System.out.println ("#of "+i+"'s: "+Dice.sum[i]) ; } } Here is the output: #of 0's: 0 #of 1's: 0 #of 2's: 0 #of 3's: 0 #of 4's: 0 #of 5's: 0 #of 6's: 0 Why didn't these two lines execute inside printDice: System.out.println (Dice.name) ; System.out.println ("value: "+Dice.x) ; if they had then i would expect to see "a1" and "Value: 0" printed at the top of the rows of #of's

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  • Garbage Collection in Java

    - by simion
    On the slides I am revising from it says the following: Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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  • Java BufferedImage increase width

    - by James Moore
    Hello, I have managed to load in an image using: BufferedImage image = ImageIO.read(out); and place text over it however, I want the text to appear next to the image. How can I increase the image width on the right to allow for space for the text to be drawn on. Or do I have to create a new empty image and insert the existing one? Thanks

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  • java - question about thread abortion and deadlock - volatile keyword

    - by Tiyoal
    Hello all, I am having some troubles to understand how I have to stop a running thread. I'll try to explain it by example. Assume the following class: public class MyThread extends Thread { protected volatile boolean running = true; public void run() { while (running) { synchronized (someObject) { while (someObject.someCondition() == false && running) { try { someObject.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } // do something useful with someObject } } } public void halt() { running = false; interrupt(); } } Assume the thread is running and the following statement is evaluated to true: while (someObject.someCondition() == false && running) Then, another thread calls MyThread.halt(). Eventhough this function sets 'running' to false (which is a volatile boolean) and interrupts the thread, the following statement is still executed: someObject.wait(); We have a deadlock. The thread will never be halted. Then I came up with this, but I am not sure if it is correct: public class MyThread extends Thread { protected volatile boolean running = true; public void run() { while (running) { synchronized (someObject) { while (someObject.someCondition() == false && running) { try { someObject.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } // do something useful with someObject } } } public void halt() { running = false; synchronized(someObject) { interrupt(); } } } Is this correct? Is this the most common way to do this? This seems like an obvious question, but I fail to come up with a solution. Thanks a lot for your help.

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  • How to implement a list fold in Java

    - by Peter Kofler
    I have a List and want to reduce it to a single value (functional programing term "fold", Ruby term "inject"), like Arrays.asList("a", "b", "c") ... fold ... "a,b,c" As I am infected with functional programing ideas (Scala), I am looking for an easier/shorter way to code it than sb = new StringBuilder for ... { append ... } sb.toString

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  • Java/Swing: low-profile button height?

    - by Jason S
    I would like to reduce the vertical size of a JButton. The following code works fine for K 1 but I can't seem to reduce the size. Any suggestions? JButton button = /* ... get button here ... */ Dimension d = button.getPreferredSize(); d.setSize(d.getWidth(), d.getHeight()*K); button.setPreferredSize(d);

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  • Clone List Elements in Java

    - by Amir Rachum
    Hi all, I have a variable of type List<RelationHeader>. Now I want to copy all the elements in this list to a new list, but I want to actually copy all the members by value (clone them). Is there a quick command to do this, or do I need to iterate over the list and copy them one at a time?

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  • Java: serial thread confinement question

    - by denis
    Assume you have a Collection(ConcurrentLinkedQueue) of Runnables with mutable state. Thread A iterates over the Collection and hands the Runnables to an ExecutorService. The run() method changes the Runnables state. The Runnable has no internal synchronization. The above is a repetitive action and the worker threads need to see the changes made by previous iterations. So a Runnable gets processed by one worker thread after another, but is never accessed by more than one thread at a time - a case of serial thread confinement(i hope ;)). The question: Will it work just with the internal synchronization of the ConcurrentLinkedQueue/ExecutorSerivce? To be more precise: If Thread A hands Runnable R to worker thread B and B changes the state of R, and then A hands R to worker thread C..does C see the modifications done by B?

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  • Java Swing how to create a task reminder

    - by newbie123
    How to create a event reminder. Example, an user created an event which is today 5.00pm and stored it into database. When ruun the program the reminder will pop up if the system time is 5.00pm. Is there any API can do that? From google what I got was those freeware.

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  • A very strange problem -> CSS file not detected .Java web application

    - by Nitesh Panchal
    Hello, If i browse my site using http://localhost:8080/abc/Login/index.jsf, everything works fine. But if browse it using simply http://localhost:8080/abc, the page is shown but all its images and css files are missing. What can be the problem? I have this in my web.xml :- <form-login-config> <form-login-page>/Login/index.jsf</form-login-page> <form-error-page>/Login/index.jsf</form-error-page> </form-login-config> Probably, images are not getting referenced correctly. Can anybody help me? I have referenced css file as follows :- <link href="./Css/MainStyleSheet.css" rel="stylesheet" type="text/css" /> where Css is folder in Login

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  • Distinguish between a single click and a double click in Java

    - by user552279
    Hi, I search the forum and see this codes: public void mouseClicked(MouseEvent e) { if (e.getClickCount() == 2) { System.out.println(" and it's a double click!"); wasDoubleClick = true; } else { Integer timerinterval = (Integer) Toolkit.getDefaultToolkit().getDesktopProperty( "awt.multiClickInterval"); timer = new Timer(timerinterval.intValue(), new ActionListener() { public void actionPerformed(ActionEvent evt) { if (wasDoubleClick) { wasDoubleClick = false; // reset flag } else { System.out.println(" and it's a simple click!"); } } }); timer.setRepeats(false); timer.start(); } } but the code runs incorrectly(Sometime it prints out " and it's a single click!" 2 times . It should print out " and it's a double click!"). Can anybody show me why? or can you give me some better ways to do this? Thank you!

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  • Java: JButton actionListener explantation

    - by MrDoctorProfessorTyler
    I am extremely confused as to how a JButton works. I have read over the oracle documents of the JButton, but I have failed to see how a JButton can have an actionlistener added to it. I have really always wondered how things like JFrames and all that can have things like .addMouseListener and all that. Can anyone explain how a JButton can have an actionListener added to it like the .addActionListener(...) syntax?

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  • Java: Comparing a class with another within that class using a my own .equals

    - by user1670252
    I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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  • how does serializable work in java?

    - by Karl Trumstedt
    If I have an instance of a class that I store in a session I need to make it serializable. This class has a static variable, will this be serialized in every instance stored? The static variable is a reference to a cache containing a lot of data in the background. Will all of this data be serialized? If so, it seems preferable to make this variable transient and re-fetch the cache instance each time the instance is restored. Maybe not store the cache instance at all in the class. Will the constructor execute when a class is restored from a serialized state? if not is there any other method I can use to re-instate a transient variable?

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  • Best Java library(ies) for forgiving command interpreter

    - by vkraemer
    I am looking for a library or set of libraries that will help me write a forgiving command interpreter. A forgiving command interpreter would be a command interpreter which can deal with simple and even not so simple spelling and word order mistakes in the input. My goal is to have an interpreter which would take the input (a command) from a user and then: execute the command, if it is correct. apply corrections to the command, until a correct command is generated and then present that command to the user to confirm whether it is 'what the user meant'.

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  • Blackberry (Java) - Setting scrolling be not focused on objects on the screen

    - by paullb
    I have a mainscreen which currently scrolls (and I have the arrows on the right) but the scrolling seems to be focused on the ButtonField objects that I have on the page. Is there any way to set the scrolling to be non-focused scrolling (moving a few pixels each time). Is there a way to set this? Other ideas I have had (which sound hacky so I want to avoid): - Placing NullFields around to scroll - Manually listening to the trackwheelRoll event and moving appropriately

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  • Update music file details - Java.

    - by Desorder
    Hi all, Well, I'm a music fan guy, and now with my 18000 music collection, it's getting very hard to maintain. So, I would like to ask I could of question to help to write an app to maintain it for me. 1- How can I access a music file and read details of it? I mean, I would like to write some code and passing the directory, my app would read all the music files (understand mp3 files) and with that I would like to access details like title, artist, length and so on... 2- Is there a public source that I could access and update my file? A webservice somewhere that I could connect, query some information based on song name, or artist or whatever. I would like to achieve a final result of given a directory, my app would read the file, collect some information and query the source for a complete list of detail and update my file. Thank you guys for any help...

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