Question about Java implementation in Linux platform

Hello,
I shall implement one Java program in Linux platform. I'm a newer to linux. Need I install some special software in Linux platform to compile and run JAVA program?
Thank you in advance
java_linux

Sorry, this forum is about Sun Studio, which is a collection of native compilers and tools. About Java, please use Java forum; for example, one of these: http://forums.sun.com/category.jspa?categoryID=5

Similar Messages

Question about Java's HttpServer: Threading? Backlog?

Hello,
I have two questions about Java's HttpServer (com.sun.net.httpserver). From the JavaDoc:
>
Management of threads can be done external to this object by providing a Executor object. If none is provided a default implementation is used.
>
How can I get information about the default implementation in 1.6.0_13? Do you know the behavior? From my observations, the default implementation uses no Threads, meaning every request is handled in the same Thread, this results in handling the requests to the HttpServer one after another.
Is this right?
The second question is about this, also from the JavaDoc:
>
When binding to an address and port number, the application can also specify an integer backlog parameter. This represents the maximum number of incoming TCP connections which the system will queue internally. [...]
>
When setting the backlog to -1, it uses the systems default backlog. How can I determine the systems default backlog? Can some lines of Java code reveal it (there is no getBeacklog() method)? Or is it up to the Operating System (we use Redhat Linux)?
Thanks a lot for your help!
Regards,
Timo

How can I determine the systems default backlog?You can't. There is no API for that even at the C level.
Can some lines of Java code reveal itNo.
Or is it up to the Operating System (we use Redhat Linux)?Yes. Linux provides a large default. It seems to be at least 50 on most platforms. This is not something you should be worrying about.

Three questions about Java and Ftp

Hello, i've the following questions about Java and Ftp:
1- .netrc file is in $HOME directory but i can't access to this directory from java code. The following line producesan Exception (directory doesn't exists)
FileWriter file = new FileWriter ("$HOME/.netrc");
2- .netrc file must have the following permissions: -rw- --- --- but when i create the .netrc file the following permissions are on default: -rw- r-- r--, how can i change this permissions? (In java code, i can't use chmod.....)
3- Are there any way to pass parameters to a .netrc file? If i get to do this i needn't change the permissions because i can't modify or create/destroy this file.
Thanks in advanced!!!
Kike

1- .netrc file is in $HOME directory but i can't
access to this directory from java code. The
following line producesan Exception (directory
doesn't exists)
FileWriter file = new FileWriter ("$HOME/.netrc");$HOME would have to be replaced by a shell, I don't
think you can use it as part of a legal path.
Instead, use System.getProperty("user.home");
Ok, thanks
2- .netrc file must have the followingpermissions:
-rw- --- --- but when i create the .netrc file the
following permissions are on default: -rw- r--r--,
how can i change this permissions? (In java code,i
can't use chmod.....)Yes, you can: Runtime.exec("chmod ...");
I need to use estrictly the .netrc with -rw- --- --- permissions
Yes, i can use Runtime.exec ("chmod ..."); but i don't like very much this solution because is a slow solution, am i right?
3- Are there any way to pass parameters to a.netrc
file? If i get to do this i needn't change the
permissions because i can't modify orcreate/destroy
this file.I don't think so. Why do you need the .netrc file in
Java at all? Writing a GUI frontend?I want to use automatic ftp in a java program and FTP server, the files and path are not always the same, so i can:
- modify .netrc (for me is the complex option)
- destroy and create a new .netrc (is easier but i have permissions problem)
- use .netrc with parameters but i haven't found any help about it
Thanks for your prompt reply!!!!
Kike

Question about Java apps structure

Hello guys,
I'm a professional C++ programmer and I would like to start learning Java. I'm reading about Java from here and there and would like to ask you about how a java program is structured compared to C++.
So in C++, I have main.cpp (or any other file name, doesn't matter), which contains a the main() function, and I have .h and .cpp class files that I instantiate (basically) in my main function to get my program to work.
In Java, I'm confused and can't really find the "general" rule to how stuff are organised. I noticed that every class has a main function (why?), and there's no global scope. And "somehow", file names must exactly be equal to the class names.
The question is: how are Java files of classes (and other stuff, if available) are arranged to create a program? What's the standard why? And How can I have many classes together in a single main()?
Thank you for any efforts :-)
Edited by: 927494 on 13.04.2012 07:02
Edited by: 927494 on 13.04.2012 09:10

Thank you guys for the replies. I still have some more doubts :-)
Do I have to have a file for the implementation and a file for the definitons, like cpp and header files? or just everything inside the class?
Why does Netbeans fail to compile when I change the class name? what should I change with the class name in general to have it compile correctly? From what I understand till now, the top level class's name (the class with the main() function that's gonna be executed) has to be equal to the file name (and I got that this is the sufficient condition for the app to compile), while the same file can have more classes if I wish. Did I get that right?
I don't know if I get that right too, we pass only a SINGLE class/file to the compiler, and it automatically resolves ALLLL the included files automatically, unlike C++, where all cpp files have to be passed to the compiler/makefile to create object files, and then the executable is created after linking all those object files with the libraries together. i.e.: Java doesn't really need a makefile because making is really simple with only 1 filename. True?

Running a perl shell command through a java program on linux platform

i'm trying to execute the following command in a java program "perl xxx.pl" using the runtime.getruntime method
here is the piece of code
String[] cmd={"perl","-c","AraMorph.pl",""};
Process p = Runtime.getRuntime().exec(cmd,null,new File("/home/ahmed/buckwalter_morphan_1/data"));
p.waitFor();
BufferedReader in=new BufferedReader(new InputStreamReader(p.getInputStream()));
String line;
while ((line=in.readLine())!=null)
System.out.println(line);
but it doesn't output anything even if i tried to print the output to a file
i'm trying to execute this program on linux platform but its working properly on a windows platform
thx
raar

String[] cmd={"perl","AraMorph.pl"," </home/ahmed/in.txt"," >/home/ahmed/ast.txt"};
Process p = Runtime.getRuntime().exec(cmd,null,new File("/home/ahmed/buckwalter_morphan_1/data"));
BufferedReader in=new BufferedReader(new InputStreamReader(p.getErrorStream()));
String line;
while ((line=in.readLine())!=null)
System.out.println(line);
p.waitFor();
String str2=p.getInputStream().toString();
System.out.println("==================================="+str2);
and it still outputs nothing but goes in something like infinite loop or as assumed in the article u suggested a deadlock but even all solutions to all pitfalls didn't succeed

Questions about Java Servlets and JSP

Hi,
I'm a confident Java Programmer (and really enjoy using this language) but am very new to Java servlets and Java Server Pages.
I have previously worked with Perl on my web projects (simple 'league' style voting pages). I read in my 'Core Java' book that I should no longer use perl or even cgi.
I need to know more about Java servlets and Java Server Pages so I can make the switch to a 'real' programming language.
I have a few questions:
How should I start to learn JS and JSP?
How applicable will the java knowlegdge I have already be?
Are JSP common on the world wide web?
What tools do I need to start? (I currently develop in JBuilder and have Java 1.4.1 Standard Edition)
Is it likey my web host (and others) will support JSP?
Thank-you very much for helping a novice get started,
Regards,
Paul

Hi, Steve ...has to be frustrating! But do not despair.
Let's suppose the servlet it's named MyServlet on package org.servlets
WEB-INF should look:
WEB-INF
classes
org
servlets
MyServlet.class
web.xml
web.xml file should have this two declarations:
<web-app>
<servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>org.servlets.MyServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
</servlet-mapping>

</web-app>Now, once the container starts (Tomcat?), you should be able to see that servlet in:
http://localhost:8080/[my-context/]MyServletAnd what my-context is? The web application context. This string should be empty if your're deploying to the root context, otherwise should the context name. In Tomcat, deploying to root context defaults to using webapps/ROOT.
Sorry for my English, but I felt the need to answer your request. I hope it helps despite my writing.

Question about Java Errors

I have some questions about some java errors
1. what kind of errors are contained in Error class?
2.does this class contain only runtime errors?
3. if the question number 2 is positive, what about InstantiationError which is a compile error and is a subclass of Error.
4.When our program is out of memory, which processes are done for an error to be produced. is the error actually from OS or VM?

I have some questions about some java errors
1. what kind of errors are contained in Error class?An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch.
2.does this class contain only runtime errors?No
3. if the question number 2 is positive, what about
InstantiationError which is a compile error and is a
subclass of Error.
4.When our program is out of memory, which processes
are done for an error to be produced. is the error
actually from OS or VM?Various - both, depending on where the error occurred.

Question about java-based server app frameworks

Hello, I am working on a Java applet application and would like to choose a Java-based scalable server framework to use within my applcation. I have found a few like xsocket or QuickServer and have a question about other. And, also, which is the one You may advise? Yours sincerely, Slawek

For online gaming server. I first heard of xsocket and started using this, but have the problem with NAT. I now know that I need to initiate connections from client behind NAT (server has a public IP) and send messages from server to client within the same connection. I am doing this the following way (as shown in examples- below), but it appears that server receives messages, but client doesnt. I dont listen on any ports in client application and just need to take advantage of the connection initiated (information go from client to server properly).
Server-
try{ nbc = pool.getNonBlockingConnection(inetAddress, 8090);
try{ nbc.write("|01|______|02|______|03|______|04|______|05|______|06|______|07|______|08|______|09|______|10|______"); }catch(Exception ee){}
}catch(java.io.IOException f){}
Client-
public boolean onData(INonBlockingConnection nbc) throws IOException,ClosedChannelException,BufferUnderflowException,MaxReadSizeExceededException{
String x = nbc.readStringByLength(100);
System.out.println("S >> C = "+x);

Some questions about Java deployment steps and techniques

All my java experience is coding and testing in my local machine (where, of course, a jre is available), but ... when I deploy to other people, they may not have a jre or they may have a different version of it than the one needed to run my application. I've read different stuff online including jars and java web start but still I have many questions.
(1) first one first, Sun contradicts common sense, when it says that i can redistribute my own customized light version of their jre by taking out some files (java.sun.com/j2se/1.5.0/jre/README). there are two ways for me to get a jre: Way one is by downloading one from Sun, the download comes as an *.exe file and I don't see how I can take files out of it, so do you know how?. Way two would be by simply copying the set of files i choose (according to that Readme) from my current jre installation (the one on my \java\jdk\jre directory), does this make sense?, (if you're under windows) doesn't an installed version of a jre need a couple of dlls plus some new registry entries?, this contradicts common sense, if I'm not wrong, that Readme is a nonsense, but since that readme is at each of us jre installation \java\jdk1.x\jre\Readme, it can't be a nonsense, therefore I'm wrong, therefore the answer is either Way 1 or Way 2, HOW? ... or maybe there's a Way 3?
(2) Say I never read that Readme so I download the jre (as an exe) to bundle it along with my application in a jar ... now I'll give my neighbor either a jar with two exes or two exes jars ... is there a way to make a jar so that two files get executed? ... if the answer is No and I have competition from a second neighbor, then I believe I'm asking my first neighbor to choose my application based on our friendship, that's not reasonable if we are doing business, so Java loses.
(3) Say that my application is a single executable file like this,
class X{
public static void main(String[]$$$){
System.out.println("Console, where are you?");
At this point, say that my neighbor accepted the two executables, he executed the jre.exe and has jre6 in his system, now he double clicks on my X.jar ... it's a console application and jar files are not associated with the java.exe launcher since java 5, but with javaw which doesn't open any console ... how do i make it so a console opens and prints "Console, where are you?" ... do I ask my neighbor-customer to add a couple of lines to his path and open his console and (please) enter java -jar jarfile.jar? ... isn't it too much? ... i hope i'm wrong cause this is kind of discouraging
(4) I've read that by installing a more recent version of a jre on a system that has an older jre (there to help other applications work), I might be causing a problem for the other applications to run ... I guess that's the reason why that Readme kind of encourage to redistribute a "private" version of a jre (one that doesn't come with a java.exe launcher ... any feedback on this?
(5) I'm reading a lot of hype about Java Web Start ... it looks better than the traditional jar/jre deployment ... but setting up a MIME type to *.jnlp, it doesn't come with some free hosting I've checked ... somebody can recommend a free hosting service that allows to set a *.jnlp MIME? (I'll appreciate a suggestion here, cause I would like to test Web Start)... and, anyhow, how you people compare it with the paradigm of the single executable file?.
Thanks. Your feedback is highly appreciated.

jorgelbanda wrote:
..(5) I'm reading a lot of hype about Java Web Start ... It's gratifying to think that someone who wants to deploy apps., has the common sense to search first! You would not guess how I often I hear "I wanna' make an EXE" shortly followed by "What's webstart?".
...it looks better than the traditional jar/jre deployment ... but setting up a MIME type to .jnlp, it doesn't come with some free hosting I've checked ... OK. You cannot define new mime types, but perhaps the site already has it defined. An easy way to check is to upload 'any old file' that ends in .jnlp and use the [mime type checker|http://pscode.org/mime/] to see what content type it is served as.
..somebody can recommend a free hosting service that allows to set a .jnlp MIME? (I'll appreciate a suggestion here, cause I would like to test Web Start)... I'm pretty sure the Google based sites offer it.
Note that I edited the asterisks out of your post, to avoid the forum software parsing half the reply as bold.

Question about java thread implementation

Hi All,
I am comparing the performance of the Dining philosopher's problem
implemented in Java, Ada, C/Pthread, and the experimental language I
have been working on.
The algorithm is very simple: let a butler to restrict entry to the
eating table, so that deadlock is prevented.
It turns out that the java code is the winner and it is 2 times faster than C!
The comparison result really surprised me, and raised a big
question mark : why java runs so fast? I did not use high-level synchronization
constructs like Semaphores, atomic variables, etc.
I vaguely recall that Java thread is actually implemented by the underlying
system thread library(so on linux, the default would be NPTL, on windows NT threads,
and on Mac OSX it would be Cthread?). Can no longer remember where I read that.
Does anyone here have some notions about the Java thread
implementations(where is this formally explained)? or Does anyone know where
I can possibly find relevant literature or the answer?
thanks a lot.
cheers,
Tony

Peter__Lawrey wrote:
google has lots of information on java threaded.
One thing java does is support biased locking. i.e. the thread which last locked an object can lock that object again faster.
This may explain the difference. [http://www.google.co.uk/search?q=java+usebiasedlocking]
Note: you can turn this option off and other locking options to see if a feature is giving you the performance advantage.
Personally I have found that real world multi-threaded applications are easier to write in Java, esp. when you have a team of developers. For this reason, alot of C/C++ libraries are single threaded, even when there would be a performance advantage in being multi-threaded (because its just too hard in reality to make it thread safe and faster because of it)I didn't know that, very interesting :-)

Question about Java RMI/JNDI/IIOP and Linux IPCHAINS.

IPChains only recognises, per se, three protocols
-TCP
-UDIP
-ICMP
as I grasp things. Can one mention IIOP
directly in an IPCHAINS firewall,
or is one forced to allow one particular IP,
by protocol and Port number?
What is recommended for RMI
and JNDI here?

Zac1234 wrote:
IPChains only recognises, per se, three protocolsipchains? Blimey, I thought iptables took over from that ages ago.
-TCP
-UDIP
-ICMP
as I grasp things. Can one mention IIOP
directly in an IPCHAINS firewall,doubt it; although you could set up a rule for it called IIOP
or is one forced to allow one particular IP,
by protocol and Port number?that'd be where I'd start
What is recommended for RMI
and JNDI here?Well according to [this page|http://en.wikipedia.org/wiki/General_Inter-ORB_Protocol]:
+"IIOP (Internet Inter-Orb Protocol) is the implementation of GIOP for TCP/IP."+
so I suspect you'll only have to worry about TCP packets. However, details of the protocol itself are something you should Google for if you want definitive answers. Alternatively, consult someone who's used to maintaining firewalls.
Winston
Edited by: YoungWinston on Apr 17, 2010 3:54 AM
PS: This is a Java forum

Some basic questions about Java ME

Hi,
I am new in the world of Java ME, I started to read about the technologies around it and for this reason I have some questions.
There are 2 platforms CDC and CLDC and on top of these platforms there are some profiles, for example Personal Profile for CDC or MIDP2 for CLDC. On the next level (on top of these profiles) are some JSRs which are treated as optional packages.
I saw that the CLDC emulator from SUN - WTK contains for example JSR 179 for Location based services and JSR 226 - SVG rendering. But the counterpart for CDC doesn't contain them.
How can these JSRs be added to the CDC stack? are there some implementations of these JSRs as jars or something like this? or on the JCP site are only the specifications of this JSRs and if someone wants to add these JSRs to an emulator (virtual machine) he should implement these specifications?
I hope that I have explained properly my "puzzle" and that someone will answer to my questions.
Thank you

1.    String[] numString = {"1","2","345678","9","abc"};
    int[] numInt = new int[numString.length];
    for (int x=0; x<numString.length; x++) {
      try {
     numInt[x] = Integer.parseInt(numString[x]);
      } catch (NumberFormatException nfe) {
     System.out.println(nfe.getMessage());
        numInt[x] = Integer.MIN_VALUE;
    }2. Best for what?

Question About Java Threads and Blocking

I'm helping someone rehost a tool from the PC to the Sun. We're using the Netbeans IDE and the Java programming language. I took a Java course several years ago, but need some help with something now. We're developing a front-end GUI using Swing to allow users to select different options to perform their tasks. I have a general question that will apply to all cases where we run an external process from the GUI. We have a "CommandProcessor" class that will call an external process using the "ProcessBuilder" class. I'm including the snippet of code below where this happens. We pass in a string which is the command we want to run. We also instantiate a class called "StreamGobbler" my coworker got off the Internet for redirecting I/O to a message window. I'm also including the "StreamGobbler" class below for reference. Here's the "CommandProcessor" class:
// Test ProcessBuilder
public class CommandProcessor {
public static void Run(String[] cmd) throws Exception {
System.out.println("inside CommandProcessor.Run function...");
Process p = new ProcessBuilder(cmd).start();
StreamGobbler s1 = new StreamGobbler("stdin", p.getInputStream());
StreamGobbler s2 = new StreamGobbler("stderr", p.getErrorStream());
s1.start();
s2.start();
//p.waitFor();
System.out.println("Process Returned");
Here's the "StreamGobbler" class:
import java.lang.*;
import java.io.*;
// Attempt to make the output of the process go to the message window
// as it is produced rather that waiting for the process to finish
public class StreamGobbler implements Runnable {
String name;
InputStream is;
Thread thread;
public StreamGobbler (String name, InputStream is){
this.name = name;
this.is = is;
public void start(){
thread = new Thread (this);
thread.start();
public void run(){
try{
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
while (true){
String s = br.readLine();
if (s == null) break;
System.out.println(s);
//messageWindow.writeToMessageArea("[" + name + "]" + s);
is.close();
catch(Exception ex){
System.out.println("Problem reading stream" + name + "...:" + ex);
ex.printStackTrace();
The "CommandProcessor" class calls two (2) instances of the "StreamGobbler" class, one for "stdin" and one for "stderr". My coworker discovered these are the 2 I/O descriptors that are needed for the external command we're running in this case. We're actually called the Concurrent Versions System (cvs) command from the GUI. Here's what we need it to do:
We want to display the output real-time as the external process is executing, but we want to block any actions being performed on the GUI itself until the process finishes. In other words, we want to show the user any generated output from the process, but don't want to alllow them to perform any other actions on the GUI until this process has finished. If we use the "waitFor()" function associated with a process, it blocks all external process output until the process has completed and then spews all the output to the screen all at once. That's NOT what we want. Also, if we don't use the "waitFor()" function, the code just continues on as it should, but we don't know how to block any actions on the GUI until this process has finished. My coworker tried the following code, but it also blocked any output until the process had finished:
while (s1.thread.isAlive() || s2.thread.isAlive())
// We really don't do anything here
I'm pretty sure we have to use threads for the output, but how do we instantly show all output and block any GUI actions?
Thank you in advance for your help!

You're talking about a GUI, but there's nothing in that code which is putting events into the GUI update thread. You also say that nothing happens to the GUI until the CommandProcessor.Run() method returns if you wait for the process.
This implies that you're calling CommandProcessor.Run() in an ActionListener. This will block the GUI thread until it completes.
I was going to explain what to do, but a quick Google informed me that there's a new class which is designed to help in these situations SwingWorker (or as a [separate library|https://swingworker.dev.java.net/] if you're not up-to-date yet).

Question about Java SE Source Code

I was wondering, what is Java SE written in? Can't be Java right? Since thats like the chicken and the egg. Can't write in Java unless you have a platform to interpret Java code into byte code, but if the platform is written in Java... what is interpreting the platform? The platform can't interpret itself right?
Little confused about it ^, I didn't post in the thread about open source Java since everyones just fighting on there about how old or new the news is. To tell ya the truth, I heard about it yesterday but didn't expect it so soon. Its nice that its here, its now fully Linux friendly. :D
I might download the code and take a look at it if its written in Java.

I was wondering, what is Java SE written in? Can't be
Java right? Since thats like the chicken and the egg.
Can't write in Java unless you have a platform to
interpret Java code into byte code, but if the
platform is written in Java... what is interpreting
the platform? The platform can't interpret itself
right?
So you write the 0.0.1 compiler and runtime in something else.
Using that you create and compile a Java version that you call 0.0.2.
You now have a compiler written in Java that can compile Java.
The runtime is a bit more complex as it needs some platform specific bootstrapping code, but most of that can be written in Java as well.
And that's no theory, it's what actually happens (and not just with Java).
Not everything is Java, but a good chunk certainly is (or can be).

Question about Java Micro Edition

Hello,
I am interested about writing a program for PDAs. These seem to be running the Java Micro Edition, so I guess this is a good choice. But what about programming the GUI with the j2me? Afaik, it does not support swing, and the specifications are so full of abbreviations that I do not undertand that I really don't know other than to simply ask here about the possibilities of GUI programming with j2me, is there a "standard" gui library for j2me, or is it device-dependant, and is it possible to install the j2me under windows/linux for developing and testing purposes?
Help please.. ;-)
Thanks
Jan

thx :) J2ME seems to be very interesting. But zeb is right with the post in the discussion thread for this article, "where to start" is an important questions. So please, sun, make it easier for us to us (hobby-)programmers to adopt J2ME..
I found this one alternatively:
www.ewesoft.com
does anyone have experiences with it?
Jan

Question about Java implementation in Linux platform

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