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  • Java side scrolling game on android

    - by hanesjw
    I'm trying to make an easy side scrolling game just to learn the ropes of game programming on android. I came up with a solution of how to make it but I don't really think it is the most elegant solution. I wanted to get some different ideas on how to implement my game, as I really have no other solution right now. Here is a quick explanation of how it works.. I basically have blocks or objects fall from the top of the screen. The blocks are defined from a pre-defined string I create using a custom 'map-editor'. I create all the blocks at compile time, position them on or off the screen and simply increment their coordinates with each iteration of the gameloop. It is actually done a little bit better then that, but that gives a short easy explanation on the basic idea. I heard from a few people that instead of incrementing each block position, have the blocks stay there and simply change the viewable area. That makes sense, but I have no idea how to do it. Can anyone share some ideas or links on how I can implement something like this? I know my current solution isn't the greatest. Thanks!

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  • Java : Singleton class instances in a Web based Application

    - by Preethi Jain
    I have this Singleton class inside a Web Application . public class MyDAO { private static MyDAO instance; private MyDAO() { } public static MyDAO getInstance() { if (instance == null) { instance = new MyDAO(); } return instance; } I will access it this way public void get_Data() { MyDAO dao = MyDAO.getInstance(); } How many Objects of MyDAO class will be created if there are 3 Users accessing the Application ?? Will there be one instance of MyDAO per User ??

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  • Validating IPv4 string in Java

    - by Mat Banik
    Bellow method is validating if string is correct IPv4 address it returns true if it is valid. Any improvements in regex and elegance would be very appreciated: public static boolean validIP(String ip) { if (ip == null || ip.isEmpty()) return false; ip = ip.trim(); if ((ip.length() < 8) & (ip.length() > 15)) return false; try { Pattern pattern = Pattern.compile("^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$"); Matcher matcher = pattern.matcher(ip); return matcher.matches(); } catch (PatternSyntaxException ex) { return false; } }

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  • Java Timer not working

    - by Jacob
    I have an Image named worldImageToUse and I have a Timer that is supposed to toggle worldImageToUse between two images every 1 second. But it does not seem to work. Help Please? public void startWorldImageFlash() { worldImageFlashTimer = new Timer(); TimerTask task = new TimerTask() { @Override public void run() { if(worldImageToUse == worldImage) setWorldImageBW(); if(worldImageToUse == worldImageBW) setWorldImageColor(); } }; worldImageFlashTimer.scheduleAtFixedRate(task, 0, 1000); } public void stopWorldImageFlash() { worldImageFlashTimer.cancel(); setWorldImageColor(); }

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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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  • [Java] Safe way of exposing keySet().

    - by Jake
    This must be a fairly common occurrence where I have a map and wish to thread-safely expose its key set: public MyClass { Map<String,String> map = // ... public final Set<String> keys() { // returns key set } } Now, if my "map" is not thread-safe, this is not safe: public final Set<String> keys() { return map.keySet(); } And neither is: public final Set<String> keys() { return Collections.unmodifiableSet(map.keySet()); } So I need to create a copy, such as: public final Set<String> keys() { return new HashSet(map.keySet()); } However, this doesn't seem safe either because that constructor traverses the elements of the parameter and add()s them. So while this copying is going on, a ConcurrentModificationException can happen. So then: public final Set<String> keys() { synchronized(map) { return new HashSet(map.keySet()); } } seems like the solution. Does this look right?

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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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  • What is the use of reflection in Java/C# etc

    - by zengr
    I was just curious, why should we use reflection in the first place? // Without reflection Foo foo = new Foo(); foo.hello(); // With reflection Class cls = Class.forName("Foo"); Object foo = cls.newInstance(); Method method = cls.getMethod("hello", null); method.invoke(foo, null); We can simply create an object and call the class's method, but why do the same using forName, newInstance and getMthod functions? To make everything dynamic?

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  • Java - Syntax Question: What is <? super T>

    - by aloh
    I'm having trouble understanding the following syntax: public class SortedList< T extends Comparable< ? super T> > extends LinkedList< T > I see that class SortedList extends LinkedList. I just don't know what T extends Comparable< ? super T> means. My understanding of it so far is that type T must be a type that implements Comparable...but what is "< ? super T "?

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  • Java Object Creation Error

    - by ikurtz
    package Sartre.Connect4; import javax.swing.*; public class ChatGUI extends JDialog { public ChatGUI(){ setTitle("Chat"); } } when i do this in another class in the same package: ChatGUI chatGUI = new ChatGUI(); i end up with a situation: Cannot Find Symbol please help?

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  • check if a line is valid or not in Java

    - by Adnan
    I would like to perform checking on the following: VALID LINES; /**/ some code */ some code /** dsfsdkf sd**/ NOT VALID LINES; /**/ //some code */ /***/ //somecode So basically if there is a line of code outside a comment it is valid, otherwise not. What would be the best way to tackle this kind of validation? Note: For */ I assume that the /* has been opened some lines before.

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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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  • Java - understanding servlets

    - by Trup
    I am working on a homework project that should implement a board game between 2 clients over an HttpServlet. I have couple of questions: 1) I read that HttpServlets must be stateless, however, for the sake of the game, I have to keep a lot of state(whose turn it is, the state of the board, etc). Do I have to keep this in the clients? Does the HttpServlet indeed have to be stateless, i.e. have no fields that track state? 2) I know that the clients will talk to the servlet via the doGet/doPost methods, but how can the servlet talk to the clients(for example, if player 1 just made a move and sent it to the servlet, the servlet has to tell client 2 what the move was). Thank you Also, if you can point me to a useful, simple example of a similar code online, I would be very grateful

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  • Transfering a set with a Wildcarded Generic to a List in Java

    - by Daniel Bingham
    I have a data type that contains a set and a method that expects List<? extends MyClass>. The data type has Set<? extends MyClass>. I need to be able to move the stuff out of the set and into the List. The order it goes into the list doesn't matter, it just needs to start keeping track of it so that it can be reordered when displayed. Suffice to say that changing the Set into a List in the data type is out of the question here. This seems pretty easy at first. Create a new method that takes a Set instead of a List, changes it into a list and then passes it on to the old method that just took a list. The problem comes in changing the set to a list. public void setData(Set<? extends MyClass> data) { List<? extends Myclass> newData = ArrayList< /* What goes here? */ >(); for(ConcordaEntityBean o : data) { newData.add(o); } setData(newData); } Obviously, I can't instantiate an ArrayList with a wildcard, it chokes. I don't know the type at that point. Is there some way to pull the type out of data and pass it to ArrayList? Can I just instantiate it with MyClass? Is there some other way to do this?

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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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  • Reading lines of data from text files using java

    - by razshan
    I have a text file with x amount of lines. each line holds a integer number. When the user clicks a button, an action is performed via actionlistener where it should list all the values as displayed on the text file. However, right now I have linenum set to 10 implying I already told the code that just work with 10 lines of the text file. So, if my text file has only 3 rows/lines of data...it will list those lines and for rest of the other 7 lines, it will spit out "null". I recall there is a way to use ellipsis to let the program know that you don't know the exact value but at the end it calculates it based on the given information. Where my given information will the number of lines with numbers(data). Below is part of the code. private class thehandler implements ActionListener{ public void actionPerformed(ActionEvent event){ BufferedReader inputFile=null; try { FileReader freader =new FileReader("Data.txt"); inputFile = new BufferedReader(freader); String MAP = ""; int linenum=10; while(linenum > 0) { linenum=linenum-1; MAP = inputFile.readLine();//read the next line until the specfic line is found System.out.println(MAP); } } catch( Exception y ) { y.printStackTrace(); } }}

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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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  • When can Java produce a NaN (with specific code question)

    - by Brent
    I'm a bit perplexed by some code I'm currently writing. I am trying to preform a specific gradient descent (main loop included below) and depending on the initial conditions I will alternatively get good looking results (perhaps 20% of the time) or everything becomes NaN (the other 80% of the time). However it seems to me that none of the operations in my code could produce NaN's when given honest numbers! My main loop is: // calculate errors delta = m1 + m2 - M; eta = f1 + f2 - F; for (int i = 0; i < numChildren; i++) { epsilon[i] = p[i]*m1+(1-p[i])*m2+q[i]*f1+(1-q[i])*f2-C[i]; } // use errors in gradient descent // set aside differences for the p's and q's float mDiff = m1 - m2; float fDiff = f1 - f2; // first update m's and f's m1 -= rate*delta; m2 -= rate*delta; f1 -= rate*eta; f2 -= rate*eta; for (int i = 0; i < numChildren; i++) { m1 -= rate*epsilon[i]*p[i]; m2 -= rate*epsilon[i]*(1-p[i]); f1 -= rate*epsilon[i]*q[i]; f2 -= rate*epsilon[i]*(1-q[i]); } // now update the p's and q's for (int i = 0; i < numChildren; i++) { p[i] -= rate*epsilon[i]*mDiff; q[i] -= rate*epsilon[i]*fDiff; } This behavior can be seen when we have rate = 0.01; M = 30; F = 30; C = {15, 25, 35, 45}; with the p[i] and q[i] chosen randomly uniformly between 0 and 1, m1 and m2 chosen randomly uniformly to add to M, and f1 and f2 chosen randomly uniformly to add up to F. Does anyone see anything that could create these NaN's?

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  • How to explicitly add a piece of code to a java project

    - by user435245
    Hi there, I’m working with Net beans IDE and I want to add a piece of code to my project in a way that the source code won’t be visible to the user who is running the project, I decided to export that piece of code as a jar file in eclipse and then add that jar file to the project. But unfortunately net beans does not let me import that. It says which it is expecting a . Or when I insert. It goes in to that class and I cannot import that jar file into the project by import instruction. Is there a command in net beans which creates and object from jar file and then makes access to the functions and classes of the jar file? Would you please give the format of that instruction? If you know a better way to do this task I would be so happy if you share it with 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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