Ask MetaFilter questions tagged with java

JRE Switcher?

devnull — Mon, 14 Dec 2009 02:28:09 -0800

What's the easiest way to switch between different JVMs? I have some applications which unfortunately require specific versions of Java from different vendors - specifically IBM Java. I also need to use Sun Java.

Is there a way to define which version of Java an applet started from the browser calls? I looked for a Firefox extension but could find none.

Just to clarify: I'm not looking to switch between different versions of Sun Java, but between the Sun JRE, IBM JRE, etc.

Anything that makes the same easy for non-applets would also be useful (i.e. without creating custom .bat files)

Java with maths, the JVM without Java

outlier — Wed, 09 Dec 2009 03:04:59 -0800

I have two (possibly naive) questions about Java that I'm looking for a 10,000 foot view on. First, what are the preferred libraries are for maths and charting? Second, what are the distinguishing points between alternative JVM languages? The aim: I have a few old programming projects (bioinformatics, data manipulation and visualisation, statistics) that I'm looking to port into the modern age. So, I'm looking towards Java and the JVM, so as to make the code easily portable and ensure its future maintainability, and possibly learn something new and useful for future work.

1. What numerics, stats and graphing libraries would people recommend within Java? In (say) Python, there's just a few obvious leaders that everyone uses (Numpy and matplotlib). For interoperability, support, longevity and a good user community, I'd like to pick the "right" ones within Java. Yet it's unclear from the wide variety available which ones are good and thriving and which are niche projects.

2. The idea of an alternative language running on the JVM is appealing, especially a dynamic language (for development speed, quick scripts, data analysis, being able to use it from a interactive prompt etc.). Coming from Python, Jython is the obvious choice but seems to be a 2nd class citizen - a bit messy, some standard libraries not complete, a bit slow, doesn't seem to have a huge development effort behind it. JRuby? Also a bit slow, and I'm not a huge fan of Ruby's peculiarities. So my eye has been drawn to Groovy and Scala. Scala in particular looks cool, and promises to be fast. Groovy looks easy although again there are possible speed issues. Any opinions or things I should look out for?

Possible useful background details: I've got years of Python and C/C++behind me, and a decent swag of Java and Ruby. Speed of execution is always important, but speed of development is even more important. I'm a great fan of Python's interactive prompt and being able to mess around with code. There's a large swag of bioinformatics libraries within Java that I can use from any JVM language so that shouldn't be a problem. The initial projects will be commandline utilities, but I don't want to be limited to that in the future: desktop apps and web services may raise their head.

Is it worth my while to learn Java Web Services?

zorro astor — Sun, 29 Nov 2009 20:48:16 -0800

Is learning Java web services a good decision in terms of the future job market? I'm trying to get into something that I hope will have a promising future in terms of employment. I've quizzed a couple of Java programmers and they say the future is REST and SOAP. I was wondering about what the Mefi community thinks.

Beginning Sony Ericsson mobile phone programming. Where to start?

tmt — Tue, 24 Nov 2009 20:30:43 -0800

Beginning Sony Ericsson mobile phone programming. Where to start? I recently picked-up an unlocked Sony Ericsson K850i to replace my poor drowned iPhone and am finding it be superior in almost every way except one very important one: 3rd party applications.

I would love to have something like OmniFocus that would allow me to sync tasks with my Google calendar. Also, the built-in email client is pretty terrible in that it only allows you to connect to one account at a time. I can't be the only person to have taken a look at the offerings currently available and participated in a communal facepalm.

I've done some preliminary Google searching in regards to J2ME programming, I'm finding a serious lack of decent applications for my phone and I think it would be beneficial to work on a project that I would use on a daily basis.

So; has anyone dabbled in J2ME programming? If so, were there any tutorials in particular that explained the process in terms that a beginner could understand?

(Also; the previously discussed topics are pretty old. Are they still relevant?)

You hit Duke. Duke is killed.

ixohoxi — Sat, 21 Nov 2009 19:18:12 -0800

I'm trying to teach myself Java by writing a simple roguelike. Can you help me figure out the architecture? I'm totally new to Java. I just installed NetBeans this evening. I've been tinkering around with the Swing library.

One of the reasons I want to learn Java is to enhance my architectural chops. I'm reasonably comfortable with OOP (mainly in PHP5, which lacks some of the more exotic OO features), and I've read a couple of books on design patterns (and I know that patterns are not a magic bullet), but I still struggle with architecture.

The specific concern I'm wondering about is how to delegate control to various parts of the program as the player negotiates menus, enters different modes and interfaces in the game, etc.

For example, the first thing the player will see is the main menu. From here, they can start a new game, load a saved one, or view the high score table.

Let's say they choose the latter. My program needs to pass control over to the class responsible for displaying the high score view. When the user dismisses that view, the system should automatically return control to the main menu.

Now let's say they start a new game. Control is passed over to the main game engine, which renders a map, player statistics, etc.

The user presses "r" to read an item from their inventory. Control is passed over to a menuing widget which displays all readable items in their backpack, and allows them to select one with the up/down keys. The player can cancel the action with Esc (which simply returns control to the previous subsystem in the chain—i.e., the main game engine), or select the highlighted item by pressing Enter.

Perhaps the player later encounters a minigame—let's say they can play blackjack to earn money. In this case, control gets passed to the blackjack class. When they decide they've had enough, control is released to whatever class spawned the blackjack game.

(Or they enter a city mode from an overworld map, then return to the overworld when leaving the city...you get the idea.)

And, of course, when the player dies, the game engine terminates and control is automatically returned to the main menu.

In other words, it's much like a call stack. I've seen a similar system used in many programs, and I think it will work well for mine.

But the web apps I'm used to programming are much more linear creatures—they only receive input (e.g., POST variables) at runtime. State is entirely simulated—when it's time to move to the next step in a process, the user is simply forwarded to a new page (which is, effectively, a whole new program).

So: does my proposed architecture (sketchy though it may be) make sense? Is there a name for it? And, most importantly, how do I implement it?

Bonus points if you can combine this with an elegant way to separate the view/UI entirely from the game logic, so I can (for example) build the initial design with a text-only interface, and then graft a graphical mode on top later.

Java quicksort

Benzle — Thu, 05 Nov 2009 15:50:11 -0800

hey java programmers, I have a beginners quicksort problem for you. I am trying to write some code in Java that will read in the numbers from a file (one # on each line of .txt file name inputted by user) put them into an array, and then run quick sort on the array, AND THEN print out the sorted array. This last part I'm having torouble with right now. I tried to format it below, but maybe copy and paste to Eclipse would be easier to read,
Errors I marked with comments, and what the error is, if anyone can help me get this to run, thanks everyone!

import java.io.*;
import java.io.File;
import java.util.Scanner;

public class sdfs {
public static void main(String[] args) throws IOException {
System.out.print("Name of file with array: ");
Scanner readIn = new Scanner(System.in);
String input = readIn.nextLine();

}

public static void testScan1(String filename) {
File file = new File(filename);
Scanner scan;
try {
int[] array = new int[5];
scan = new Scanner(file);
} catch (java.io.FileNotFoundException e) {
System.out.println("couldn't open. file not found ");
return;
}
while (scan.hasNext()) {
for (int i = 0; i <> pivot)
j--;
if (i <= j) {
tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
i++;
j--;
}
}
return i;
}

void quickSort(int[] arr, int left, int right) {
int index = partition(arr, left, right);
if (left < (index - 1)) {
;
}
quickSort(arr, left, index - 1);
if (index < right) {
quickSort(arr, index, right);
}
}
}

The Spinner of War

brozek — Sat, 24 Oct 2009 12:30:11 -0800

How difficult would it be to modify/simplify this Java spinner so I can better model war for my Intro to International Relations class? I've used the NCTM's probability spinner in my Intro to International Relations class the last couple terms, and if possible, I'd like to modify it slightly to fit my activity slightly better.

I use the spinner as part of a class activity on bargaining and war. Pairs or groups of students are asked to divide a resource (something tangible - candy or laundry money, depending on how generous I feel that term) either through negotiation or by "war" (spinning the spinner). It costs a couple candy bars or some quarters to spin, but one player will get all of the remaining resource.* Sometimes the probabilities are even, sometimes they're lopsided, sometimes there's a third option in which all of the MiniSnickers go into my tummy, and sometimes the probabilities are hidden from the players. It's been a popular activity, and a handful of students enroll in the class every term because they've heard about it from their friends.

The NCTM probability spinner has worked reasonably well every time I've used it, but I think I make the activity work better with some minor (I hope) modifications. In particular, I'd like a spinner that:

-Doesn't return extraneous information (extraneous for my purposes, that is) - number of spins, results frame, cumulative experimental/theoretical counts.
-Allows for private/hidden probabilities. When I work with the NCTM spinner, I have to turn the projector off to hide them, and then wait for it to warm back up for the big reveal.

Basically, the NCTM's spinner is a fantastic way to illustrate probability and large-sample properties, but I'd like to make it fit my bargaining game more closely.

The big challenge - I have zero experience with Java. If it matters, I work in R and typeset with LaTeX, so I have some experience with ridiculous programming languages. Is it possible to modify the NCTM's spinner easily? Should I just find a student who can do it and pay him/her to do it for me?

View Page Source shows me what seems to be the code, but I'm guessing Spinner.class is another set of code that's being referenced.

var AppClass ="Spinner.class";
var AppWidth = "600";
var AppHeight= "700";
var Version1Dir = "";
var OtherTags = "codebase=tools/spinner/";
var EmbedStyleParams = "num_sects=\"4\" isAdjustable=\"true\"";
var Params = "";

*It's James Fearon's argument, basically - in bargaining situations, war is inherently costly, and a negotiated settlement that leaves both players better off always exists.

Where did my Little Java Link Go ?

duckus — Wed, 14 Oct 2009 08:36:21 -0800

I found a great Java programming site awhile back. I was given a programming task and could get immediate feedback on whether or not it was correct. Tasks were things like, test if two integers are equal and 'reverse a string'. It was targeted toward learning .. but I seem to recall the tasks had advancing levels of complexity. This is not Java BlackBelt. I can't believe I didn't bookmark it. Anyone know what I'm talking about?

Help me chat!

yoyoceramic — Thu, 08 Oct 2009 15:55:48 -0800

Asking for a friend: Java/action script 3 question - Remote Shared Object Question with Red5 Flash Server and Flash AS3 Hello,

I am trying to create a simple chat client using the red5 media server, but I seem to be having a slight hiccup. I am creating a shared object on the server side, and it seems to be creating it successfully. However, when I make changes to the object via the client (type a message), the SYNC event fires, but the content within the shared object remains empty. I suspect I am doing something wrong on the java end, any advice?

Console Results:

Success!

Server Message: clear

Server Message: [object Object]

Local message: asdf

Server Message: change

Server Message: [object Object]

Local message: fdsa

Server Message: change

Server Message: [object Object]

Local message: fewa

Server Message: change

Server Message: [object Object]

Server Side:

public class Application extends ApplicationAdapter {

private IScope appScope;

// private static final Log log = LogFactory.getLog( Application.class );

/** {@inheritDoc} */

@Override

public boolean connect(IConnection conn, IScope scope, Object[] params) {

appScope = scope;

createSharedObject(appScope, "generalChat", false); // Creates general chat shared object

return true;

}

/** {@inheritDoc} */

@Override

public void disconnect(IConnection conn, IScope scope) {

super.disconnect(conn, scope);

}

public void updateChat(Object[] params)

{

ISharedObject so = getSharedObject(appScope, "generalChat"); // Declares and stores general chat data in general chat shared object

so.setAttribute("point", params[0]);

}

Client Side:

public class SOConnect extends MovieClip

{

// Variables

var nc:NetConnection = null;

var so:SharedObject;

public function SOConnect():void

{

}

public function connect():void

{

// Create a NetConnection and connect to red5

nc = new NetConnection();

nc.addEventListener(NetStatusEvent.NET_STATUS, netStatusHandler);

nc.connect("rtmp://localhost/chatTest");

// Create a StoredObject for general chat

so = SharedObject.getRemote("generalChat", nc.uri, false);

so.connect(nc);

so.addEventListener(SyncEvent.SYNC, receiveChat)

}

public function sendChat(msg:String)

{

trace ("Local message: " + msg);

nc.call("updateChat", null, msg)

}

public function receiveChat(e:SyncEvent):void

{

for (var i in e.changeList)

{

trace ("Server Message: " + e.changeList[i].code)

trace ("Server Message: " + e.changeList[i])

}

}

// Given result, determine successful connection

private function netStatusHandler(e:NetStatusEvent):void

{

if (e.info.code == "NetConnection.Connect.Success")

{

trace("Success!");

}

else

{

trace("Failure!\n");

trace(e.info.code);

}

}

}

Being both squinty and angry is getting too much for me

Dr Dracator — Tue, 29 Sep 2009 06:15:38 -0800

How do I increase the font size for Java applications using Mtoolkit AWT in Linux? I'm trying to run iReport [ which is constantly crashing, but that's another story ], but the default font size looks tiny on my monitor. My google skills are failing me, and my overall Java experience is miserable.

I don't care to mess up my otherwise properly configured settings, just the Java ~~crap~~ applications.

I am horribly failing to use this program under xmonad on slackware (yes, I know), which means the winning answer probably involves pawing around some config file or other, not your favorite graphical configuration tool.

Python vs java in threading

xmutex — Mon, 14 Sep 2009 10:54:07 -0800

How do you respond to a dude who says that python ain't _really_ a multithreading language, and you should write it in Java- and you really think that's wrong?

How can I quickly match one of 150 million names to a code?

bottlebrushtree — Thu, 03 Sep 2009 10:10:55 -0800

I have up to 150 million product names, I need to match each of them to 1 or more codes. How can I do this very quickly and with little infrastructure requirements? Basically, up to 100,000 names will be checked against the master list of 150 million to see if they are on that specific list (they may not be). If they are on that list, the system will return one or more codes back. While I'm sure I can use a database for this activity, I'd love to hear other suggestions for alternatives such as a specific disk backed HashMap or other similar technology. A Java based or solution with Java bindings would be preferred. The system could possible dedicate up to 1GB of Ram in a transient fashion to this lookup (though much less would be preferred).

The names and mappings to code are relatively static, changing once a month at their maximum. I can pre-generate a digested format if that is required for the library to work.

A name is a string up to 255 characters, a code is a Java Int.

This would need to run on a single system running 64 bit Java JDK 1.5.0 and I'd rather that the solution use in process communication instead of network communication.

A solution using a single digested custom data file and a single Java jar library would be very nice.

Thank in advance.

Wordpress plugin incompatibility

Danniman — Mon, 31 Aug 2009 12:09:59 -0800

Wordpress Filter: Plugin incompatibility with my theme - website screws up on IE. How do I fix it? 2 of my plugins (Contact Form 7, Post Tabs) give a java script error when enabled on this site. The js error doesn't do much in firefox but it renders the whole site disfunctional in IE ( drop down nav doesn't work, tabs under the headline slider don't work, etc).

In IE, when I have debugging enabled, I get an error pop-up stating that there is a error on Line 89. After I click "debug", this is what is shown:

Microsoft JScript runtime error: Object doesn't support this property or method

Inside the file, the following code is highlighted on line 89:

{return jQuery.easing[jQuery.easing.def](x,t,b,c,d);}

So how do I fix this issue in IE? Do I need to contact the plugin author to check if they are using the latest jQuery? ( the theme author says that he is using the latest jQuery) Is there any way around this issue?

Are dereferenced open streams implicitly closed?

nikkorizz — Fri, 28 Aug 2009 08:32:03 -0800

Java filter: Are dereferenced InputStreams implicitly closed?



InputStream s;

s = new InputStream(filename1);



...  // filename1 is read and used.



// Ok, I'm done with filename1, but I want to reuse s to open filename2



s = new InputStream(filename2);

Does calling a new instance of s implicitly call s.close() to close the filename1 stream before opening the new stream?

Or is filename1 stream just now dereferenced open stream?

I ask because I ran into the "too many files open" exception when I ran my program on Fedora. So, while I was in the process of cleaning up my code and making sure I closed all InputStreams, it dawned on me that reusing an InputStream variable without first explicitly calling close() might not close the old stream. Is this true?

Also, I'm aware that you can increase the # of open files limit in Linux, but I'd rather stick to good coding practices instead of a band-aid solution.

Eclipse (IDE) problems

NormandyJack — Mon, 10 Aug 2009 07:45:44 -0800

Looking for help on an Eclipse (IDE) context launching (i.e. Right click + "run as") problem. Basically, this feature has stopped working. I know this question is probably over technical for AskMeFi (so sorry), but i thought I'd give it a shot in case someone here has had the same problem and knows how to fix it. (and i don't really belong to more than one of the appropriate forums).

This is a problem I've encountered a few times over the years, and one i usually just solve by starting over (fresh version of eclipse + new workspace).

The problem is with context launching (i.e. Running an application, setting up a run configuration via a right click on the resource you want to run, or otherwise running the currently selected resource rather than the most recently launched resource).

The problem is that this functionality has disappeared on me. Eclipse will always launch the previous configuration unless I specifically select another configuration via the run drop down, or run configurations dialogue.

I’ve looked in all the obvious places “Launch the selected resource or active editor” is selected. “If not launchable: Launch the associated project” is also selected.
The java applications I’m trying to launch do have correct “main” method signatures, so that’s not the problem either.

Any help resolving this issue would be MUCH appreciated.

I’m currently having this problem in Eclipse 3.4.0, developing java projects, few if any non-default plug-ins.

-Jack

Hosting Gametable on Amazon S3 or Linux Hosting Account?

royalsong — Wed, 05 Aug 2009 10:10:31 -0800

My friends and I use a java based program called Gametable to play long distance Dungeons and Dragons. We're having trouble finding someone who can host the game each week. Firewalls and general computer problems are preventing one of us from hosting the game. Can I use my linux hosting account (or even better my Amazon s3 account) to host Gametable? I don't have the knowledge to do complicated coding outside html and css. If it's relevant.

Creating video from a program help

JohnGL — Thu, 09 Jul 2009 16:16:24 -0800

I'm looking for a library, package, product or some sample code in either JAVA or Visual Basic that would allow me to create a video from my program. I have some software tools I've developed and I'd like some functionality to my program that could take existing video clips and pictures and then assemble them into a video. I would like the final video format to be FLV however any popular format would do. Any help would be greatly appreciated. Have a great one.

Wasn't broken but Apple fixed it anyhow

R_Nebblesworth — Wed, 08 Jul 2009 08:45:39 -0800

Why did the latest OS X update break Java and how do I fix it? Pretty self explanatory, but - I recently updated me MacBook to 10.5.7. Now, numerous websites employing Java interfaces don't work at all, or only work partially. For instance, clicking various buttons (e.g. "Login" - pretty crucial) does nothing on some of these, like Westlaw which I use for both school and work (I'm a law student). On others, Java and now that I think of it, Flash-based entities just never load - what I'm talking about here is stuff like games on armorgames.com or whatever.

Is this just me or are other people running into this? Any way to fix it? It happens in Firefox and Safari but seems worse in Safari.

Which host offers the most interpreters?

grumblebee — Fri, 05 Jun 2009 09:20:19 -0800

Is there a reliable, not-too-expensive hosting company out there that lets you post server scripts in most open-source languages? This is for personal use. I know PHP and I'm learning Python. Eventually, I want to learn Java and one of the popular functional languages. And maybe some C++.

I know I could just download the various interpreters and compilers and play around locally, but it's so much more fun writing web apps for public consumption.

Currently, I'm with Dreamhost, and they let me code in PHP and Python. Is there another host out there with more options?

I know I could get my own dedicated server or use Amazon's cloud service, but those would be expensive solutions -- wouldn't they? If that's the only way to go, help me find the most reasonable option. I'm talking personal website stuff here. I currently pay $30 a month to Dreamhost. I'd pay a bit more than that if necessary, but I'd rather not pay hundreds a month.

A Toast To The Host That Can Boast The Most Roast

yalestar — Tue, 21 Apr 2009 18:48:31 -0800

Is it cheaper to host my own site even if it means leaving my computer running 24/7? My ISP recently started offering static IP addresses for $5.95/mo, which would allow me to host my own Java/Tomcat site. Since it's nigh on impossible to find Java hosting that is both decent and inexpensive and allows me full access and control, this seems like a no-brainer. I realize there are a few variables involved here, but generally speaking, would the cost of leaving my PC on 24/7 negate the savings of hosting my own site?

Seeking books/resources on working with other people's code.

giggleknickers — Tue, 21 Apr 2009 06:33:44 -0800

I would like to find some books that cover how to work with other people's code. I'm a student and an intermediate level java programmer. I am working with someone else's code on a major project for the first time ever. I am quite used to developing projects from scratch, but trying to make sense of someone else's code is a nightmare, especially since it is very poorly written.

The program is "done" and my job is to make it better. Fix bugs, clean up the awfully written code, etc.

There are so many books on how to develop software from the beginning. Are there any books on how to take pre-existing software and give it an overhaul?

Need a book recommendation for J2EE

smurdah — Fri, 17 Apr 2009 10:46:47 -0800

I'd like to learn more about design patterns and designing a maintainable infrastructure for a J2EE web application. Do you have any book recommendations?

XCodes mysterious death

lukeo05 — Wed, 01 Apr 2009 06:09:01 -0800

Why has XCode suddenly completely stopped working? Reinstallation has done nothing. It seemed to be working one day and then the next not at all, with no obvious changes to my system that I can think of. I am using XCode 3.0 on a unibody macbook, 10.5.6. XCode seemed to suddenly stop working about a month ago, giving me this error when I type open blahblah.java in the shell:

LSOpenFromURLSpec() failed with error -10810 for the file /Users/lukeo05/blah/blahblah.java

and when I try and open XCode graphically, either with a file or just the app by itself, I get a 'This program has quit unexpectedly' error as it starts to load up, then nothing. The details of this error have this line which may be useful out of everything it says:

Application Specific Information:
objc[8690]: '/System/Library/PrivateFrameworks/DebugSymbols.framework/Versions/A/DebugSymbols' was not compiled with -fobjc-gc or -fobjc-gc-only, but the application requires GC
objc[8690]: *** GC capability of application and some libraries did not match

I have tried reinstalling XCode, and the problem persists, so I was wondering if anyone has experienced this before and any ideas what might be the issue.

Python or Java ...

eebs — Fri, 20 Mar 2009 14:13:52 -0800

Help me choose between Python and Java for a specific type of programming. Background: I am a researcher in engineering with a wide scope. Mostly, I perform simulations of (mechanical) systems, behavior of which are governed by differential equations. I also develop models for biology/genetics (but not bioinformatics type stuff). I use Fortran (I know) for programming, write results to output file(s) and read them using Excel or Tecplot to visualize. I also use Matlab and Mathematica for quick models. It gets pretty cumbersome after a while, especially when you want to quickly figure out behavior change (of a phenomenon) depending on the input variables. So I thought maybe it is time for me to learn some OOP and write codes that will allow me to change input variables interactively and see the results simultaneously on the screen. Following link best describes the type of interface I am looking for:

http://cmol.nbi.dk/models/igroup/igroup.html

You see what I mean? There are buttons, sliders, text boxes to change variables and the results change immediately in the "graphics" area. As far as I can tell, it is an applet written using Java. Let's drop the ability to write applets aside because I am not looking for that.

First question: can one write a code that would provide similar interface (GUI if you will) using Python?

If so, would it be pretty straight forward after some Python learning (I understand it is hard to answer this question but give it whirl please)?

Java appears a little intimidating to me while my initial experience with Python has been pleasant. However, I could not find any applications/codes on Python sites that fits what I am looking for (suggestions are welcome).

Thanks so much.

GPLFilter

Alterscape — Mon, 16 Mar 2009 10:19:19 -0800

Software license filter: Using a GPL-licensed library with a questionably-licensed JNI binding layer. What implications does this have for Java code that links to the JNI layer? I'm writing closed-source Java code as a research assistant in a university. So far, my code links only to GPLv2 w/classpath exception software, primarily the NetBeans RCP. A collaborator of mine has contributed a patch that requires the GLPK GNU library, which is licensed under GPLv3 (no classpath exception). The patch uses the GLPK Java Interface, which does not distribute source and does not list a license on the page or in the downloaded package.

The question: If I use the GLPK Java Interface, must I relicense my code under GPLv3 to be consistent with the GLPK's license?

(The technicalities of if I can do so are between the university lawyers and I, I suspect, and while I would love to open source this project, I'm not sure I have the ability to do so, and may need to investigate other closed-source solutions).