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  • Java iterative vs recursive

    - by user1389813
    Can anyone explain why the following recursive method is faster than the iterative one (Both are doing it string concatenation) ? Isn't the iterative approach suppose to beat up the recursive one ? plus each recursive call adds a new layer on top of the stack which can be very space inefficient. private static void string_concat(StringBuilder sb, int count){ if(count >= 9999) return; string_concat(sb.append(count), count+1); } public static void main(String [] arg){ long s = System.currentTimeMillis(); StringBuilder sb = new StringBuilder(); for(int i = 0; i < 9999; i++){ sb.append(i); } System.out.println(System.currentTimeMillis()-s); s = System.currentTimeMillis(); string_concat(new StringBuilder(),0); System.out.println(System.currentTimeMillis()-s); } I ran the program multiple time, and the recursive one always ends up 3-4 times faster than the iterative one. What could be the main reason there that is causing the iterative one slower ?

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  • Java - String Pool

    - by Gogi
    What is meant by String Pool ? What is difference between the following declarations : String s="hello"; String s=new String("hello"); Is there any difference between the Storing of this two strings by JVM ?

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  • JAVA: How do I accept input during a certain period of time only

    - by sebrock
    Im trying to do a simple game where I continually need input from players. This needs to happen during a certain time period only. Everything that is sent after that will be discarded. After the time period a new game starts. So: Start game Wait for input from all players during 10 seconds 10 secs no more input Calculate the winner and do some stuff Goto 1. I was thinking using a timer and timertask to keep track of time and maybe use a boolean variable that changes from "open" to "closed" after 10 seconds? Please give me some advise on this.

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  • Java Swing Forms Catching Data

    - by RhigoHR
    Hi everybody, I have a form in swing with a lot of textfields receiving data, then, the idea is when a click on a botton, the app catch all the data from the textfields. Do you know a good practice for this?, or is it necessary to catch textfield by textfield to get the data?.. Thx for your time.

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  • different for loops java

    - by Ayrton
    I'm having some difficulties with the following problem: I'm making a little game where you're at a specific spot and each spot has each some possible directions. The available directions are N(ord),E(ast),S,W . I use the function getPosDirections to get the possible directions of that spot. The function returns the directions into an ArrayList<String> e.g. for spot J3: [E,W] Now the game goes like this: 2 dice will be rolled so you get a number between 2 and 12, this number represents the number of steps you can make. What I want is an ArrayList of all the possible routes e.g.: I throw 3 and I'm currently at spot J3: [[E,N,E],[E,N,S],[E,S,E],[E,S,S],[W,N,E],[W,N,S],[W,S,E],[W,S,S]] How would obtain the last mentioned Array(list)?

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  • Can I add a java portlet to an existing java Web App?

    - by user323561
    Hi. I'm building a webapp that uses jboss-seam with jsf, facelets and rich faces, running on top of jboss AS 5.1. I would like to add a portlet area where I could add my own portlets, but from what I got (reading forums and documentation) I need to be running a portlet container/portal (something like liferay or gatein). But I don't want to be running a portal. I just want some kind of control where I can embed a portlet (something like an iFrame). Is this true or I got it wrong? If I'm wrong, how can I add an area to my webapp where I can add a portlet? Thanks Best regards.

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  • Java - Does null variable require space in memory

    - by Yatendra Goel
    class CheckStore { private String displayText; private boolean state; private String meaningfulText; private URL url; public CheckStore(String text, boolean state) { this.displayText = text; this.state = state; } : : } As I am initializing only two variables (displayText and state) in the constructor, Will the rest two variables (meaningfulText and url which will have the value null) will require space in memory to store null value. Q1. I think they will require space. If they will, then how much memory does a null value takes in the memory (like int takes 4 bytes). Q2. How much space a string takes in memory. I guess it will depend on the length of the string. So how much space a string takes of how much length?

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  • Help making a button open another app with Java/Android

    - by user569503
    I am trying to learn to make a simple app that opens a couple of other apps to eliminate the need for another apps. I just can't figure it out. From reading here and other places it seems this should work. Button batteryhistory = (Button)findViewById(R.string.BatteryHistoryButtonDialog); batteryhistory.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Intent i = new Intent(); ComponentName n = new ComponentName("com.android.settings", "com.android.settings.BatteryHistory"); i.setComponent(n); startActivity(i); Thanks so much for the help :D

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  • Problems reading text file data in Java

    - by user1828401
    I have this code: BufferedReader br =new BufferedReader(new FileReader("userdetails.txt")); String str; ArrayList<String> stringList = new ArrayList<String>(); while ((str=br.readLine())!=null){ String datavalue [] = str.split(","); String category = datavalue[0]; String value = datavalue[1]; stringList.add(category); stringList.add(value); } br.close(); it works when the variables category and value do not have a comma(,),however the values in the variable value does contain commas.Is there a way that I can split the index of the without using comma?

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  • Java - Thread - Problem in one of the Sun's tutorial

    - by Yatendra Goel
    I was reading this Sun's tutorial on Thread. I found a block of code there which I think can be replaced by a code of fewer lines. I wonder why Sun's expert programmers followed that long way when the task can be accomplished with a code of fewer lines. I am asking this question so as to know that if I am missing something that the tutorial wants to convey. The block of code is as follows: t.start(); threadMessage("Waiting for MessageLoop thread to finish"); //loop until MessageLoop thread exits while (t.isAlive()) { threadMessage("Still waiting..."); //Wait maximum of 1 second for MessageLoop thread to //finish. t.join(1000); if (((System.currentTimeMillis() - startTime) > patience) && t.isAlive()) { threadMessage("Tired of waiting!"); t.interrupt(); //Shouldn't be long now -- wait indefinitely t.join(); } } threadMessage("Finally!"); I think that the above code can be replaced by the following: t.start(); t.join(patience); // InterruptedException is thrown by the main method so no need to handle it if(t.isAlive()) { // t's thread couldn't finish in the patience time threadMessage("Tired of waiting!"); t.interrupt(); t.join(); } threadMessage("Finally!");

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  • Parsing XML with XPath in Java

    - by Mg
    I have a XML with a structure similar to this: <category> <subCategoryList> <category> </category> <category> <!--and so on --> </category> </subCategoryList> </category> I have a Category class that has a subcategory list (List<Category>). I'm trying to parse this XML file with XPath, but I can't get the child categories of a category. How can I do this with XPath? is there a better way to do this? Thanks in advance.

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  • java switch case question

    - by hkvega
    public String sizeOfSupermarket() { String size; switch (this.numberOfProducts) { case (this.numberOfProducts > 5000): size = "Large"; break; case (this.numberOfProducts > 2000 && this.numberOfProducts < 5000): size = "Medium"; break; case (this.numberOfProducts < 2000): size = "Small"; break; } return size; } the above is wrong, how to write the compare statement in case statement?

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  • Is there a faster method to match an arbitrary String to month name in Java

    - by jonc
    Hello, I want to determine if a string is the name of a month and I want to do it relatively quickly. The function that is currently stuck in my brain is something like: boolean isaMonth( String str ) { String[] months = DateFormatSymbols.getInstance().getMonths(); String[] shortMonths = DateFormatSymbols.getInstance().getShortMonths(); int i; for( i = 0; i<months.length(); ++i;) { if( months[i].equals(str) ) return true; if( shortMonths[i].equals(str ) return true; } return false; } However, I will be processing lots of text, passed one string at a time to this function, and most of the time I will be getting the worst case of going through the entire loop and returning false. I saw another question that talked about a Regex to match a month name and a year which could be adapted for this situation. Would the Regex be faster? Is there any other solution that might be faster?

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  • Memory increases with Java UDP Server

    - by Trevor
    I have a simple UDP server that creates a new thread for processing incoming data. While testing it by sending about 100 packets/second I notice that it's memory usage continues to increase. Is there any leak evident from my code below? Here is the code for the server. public class UDPServer { public static void main(String[] args) { UDPServer server = new UDPServer(15001); server.start(); } private int port; public UDPServer(int port) { this.port = port; } public void start() { try { DatagramSocket ss = new DatagramSocket(this.port); while(true) { byte[] data = new byte[1412]; DatagramPacket receivePacket = new DatagramPacket(data, data.length); ss.receive(receivePacket); new DataHandler(receivePacket.getData()).start(); } } catch (IOException e) { e.printStackTrace(); } } } Here is the code for the new thread that processes the data. For now, the run() method doesn't do anything. public class DataHandler extends Thread { private byte[] data; public DataHandler(byte[] data) { this.data = data; } @Override public void run() { System.out.println("run"); } }

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  • Hiding "Print to file" in a Java print dialog

    - by Carl Smotricz
    I'm maintaining this Swing app that has a "print" option. Users need to be kept from interacting in any way with the underlying file system, but the print dialog offers "print to file" as one printer, and that of course allows selecting a directory and file from the file system. Is there a painless way to override/modify the print dialog to hide the "to file" printer from this dialog? I understand the API will let me do this piecemeal but I'd rather not have to re-create most of the dialog GUI and functionality to do this.

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  • Java reading files......

    - by user69514
    Ok this is a homework questions, but I cannot find the answer anywhere, not even in the book. Path to Files If the user wants to specify a path for a file, the typical forward slash is replaced by ________. can you help?

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  • My Java regex isn't capturing the group

    - by Geo
    I'm trying to match the username with a regex. Please don't suggest a split. USERNAME=geo Here's my code: String input = "USERNAME=geo"; Pattern pat = Pattern.compile("USERNAME=(\\w+)"); Matcher mat = pat.matcher(input); if(mat.find()) { System.out.println(mat.group()); } why doesn't it find geo in the group? I noticed that if I use the .group(1), it finds the username. However the group method contains USERNAME=geo. Why?

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  • what databases can be used with java?

    - by aadersh patel
    I am doing an undergrad final project, and need to justify my choice of MySQL for the database element of my project. Truth is, it's the only one I can really use, and hence I went for it. What other database systems could I have used? Any advantages and disadvantages of these over MySQL?

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