How a java program is executed ?

Hi,
I would like to understand what a java program calls at first. Is it the main() ?
Is it the same as C++ ?
Is it different for an applet?
thanks
djb

For an application, yes, public static void main(String[] args)
(unlike C++ you cannot have main return an int, and it must have a String[] as a parameter)
For an applet it calls public void init(), then usually public void start()
Cheers,
Radish21

Similar Messages

How can java programs execute automatically when it connects to network

Good Day dears...
How can java programs execute automatically when it connects to network.
Thanks in Advance friends Shackir

884924 wrote:
Good Day dears...
How can java programs execute automatically when it connects to network.What is "it"? That is, execute when what connects to the network?
Your computer? If that's what you mean, this is not a Java question. It's an OS operational/administrative question. Executing any program, whether written in Java or not, based on some system event has to do with that system, not with the program. If it's possible to do this, you'd do it exactly the same way for a Java program as you would for any other program.
Or is "it" the program itself? If this is what you mean, then it's a nonsensical question. For the program to connect to the network and detect that it has connected to the network, it must already be executing, so asking how to execute it at that point is meaningless.
Finally, I'll point out that "connecting to the network" is a pretty meaningless phrase. Or rather, it has so many potentially valid meanings that it's impossible to know which one you're referring to when you use that phrase. And I'd be willing to bet you don't have a clear picture of that yourself.

Disallow java program to execute external command

How to disallow java program to execute some external command.
Thank.

It work by using custom policy, thank
Test.java
        String command1[] = {"/bin/ls","-a,","-l"};
        String command2[] = {"/bin/pwd"};
        Runtime runtime = Runtime.getRuntime();
        try{
            Process p1 = runtime.exec(command1);
            Process p2 = runtime.exec(command2); // AccessControlException: access denied
            Scanner s1 = new Scanner(p1.getInputStream());
            Scanner s2 = new Scanner(p2.getInputStream());
            System.out.println(s1.nextLine());
            System.out.println(s2.nextLine());
        }catch(Exception ex){
           ex.printStackTrace();
        }java.policy
grant{
   permission java.io.FilePermission "/bin/ls", "execute";
}Run
$java -Djava.security.manager -Djava.security.policy=java.policy Test
java.security.AccessControlException: access denied (java.io.FilePermission /bin/pwd execute)

Speed at which JAVA programs are executed

While it is true that a typical JAVA program will execute slower than an equivalent program written in other languages such as C++.
Is it because the compiled bytecodes (.class) have to be interpreted by the JVM?
Thanks.

yep, a .class is bytecode... the JVM interprets the bytecode "on the fly".
The JVM's major task is to "interpolate" native operating system requests. That's why the JVM is platform specific.
The bytecode to native interpretation takes a few clock ticks, so it's a might slower than native compiled code... but it's practically important to realise that this is not the big performance hit inherent in a "Virtual Machine"... the big (potential) performance loss is the overhead of "interpolating" every single O/S interface request... hence String BufferedReader.readLine() is light-years faster than char InputStream.read(), because .read() has to (1) interpret your request, (2) set the registers, (3) do an operating system interupt, (3) interpret the response... for EVERY SINGLE EENY WEENY CHARACTER... which in practice means you can't do an usable java port of directX... which is a shame really.
But is does mean that you can (almost) write a webapp which is completely portable across platforms (with zero code change).
horses....
keith.
Message was edited by:
corlettk

How to write a JAVA program to execute the SQL queries

I have a database in the Microsoft Access queries and I need to execute the query by some how write the Java program to make it execute the query. because I need to get the different of time so I know how fast each query run.
Thank you

You need jdbc-driver for MSAccess for run this example:
JDBCClient.java
import java.util.Properties;
import java.lang.String;
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.BufferedOutputStream;
import java.lang.System;
import java.lang.Class;
import java.sql.SQLException;
import java.util.Date;
import java.util.Locale;
import java.text.DateFormat;
import java.sql.Time;
public class JDBCClient{
    private String DriverName = new String();
    private String DatabaseURL = new String();
    private String UserName = new String();
    private String Password = new String();
    private String SQLFile = new String();
    private String OutputFile = new String();
    private String Separator = new String();
    private boolean NeedColumnHeaders;
    private String EncodingParamName = new String();
    private String EncodingValue = new String();
    private String OutputEncoding = new String();
    private boolean AfterLastColumnSeparator;
    JDBCClient( String propfilename){
     System.out.println( "Initializing...");
     Properties properties = new Properties();
     try{
         properties.load( new FileInputStream( propfilename));
     catch( Exception e){
             System.out.println( "Error: " + e.toString());
         System.exit( 0);
     DriverName = properties.getProperty( "DriverName");
     DatabaseURL = properties.getProperty( "DatabaseURL");
     UserName = properties.getProperty( "UserName");
     Password = properties.getProperty( "Password");
     SQLFile = properties.getProperty( "SQLFile");
     OutputFile = properties.getProperty( "OutputFile");
     Separator = properties.getProperty( "Separator");
     if( properties.getProperty( "NeedColumnHeaders").compareToIgnoreCase( "yes") == 0 ||
         properties.getProperty( "NeedColumnHeaders").compareToIgnoreCase( "true") == 0)
         NeedColumnHeaders = true;
     else
     if( properties.getProperty( "NeedColumnHeaders").compareToIgnoreCase( "no") == 0 ||
         properties.getProperty( "NeedColumnHeaders").compareToIgnoreCase( "false") == 0)
         NeedColumnHeaders = false;
     else{
             System.out.println( "Invalid value for \"NeedColumnHeaders\" property (logical expected)");
         System.exit( 0);
     EncodingParamName = properties.getProperty( "EncodingParamName");
     EncodingValue = properties.getProperty( "EncodingValue");
     OutputEncoding = properties.getProperty( "OutputEncoding");
     if( properties.getProperty( "AfterLastColumnSeparator").compareToIgnoreCase( "yes") == 0 ||
         properties.getProperty( "AfterLastColumnSeparator").compareToIgnoreCase( "true") == 0)
         AfterLastColumnSeparator = true;
     else
     if( properties.getProperty( "AfterLastColumnSeparator").compareToIgnoreCase( "no") == 0 ||
         properties.getProperty( "AfterLastColumnSeparator").compareToIgnoreCase( "false") == 0)
         AfterLastColumnSeparator = false;
     else{
             System.out.println( "Invalid value for \"AfterLastColumnSeparator\" property (logical expected)");
         System.exit( 0);
     try{
         byte[] EOL = new byte[2];
         EOL[0] = 13;
         EOL[1] = 10;
         Class.forName( DriverName);
         Properties connInfo = new Properties();
         connInfo.put( "user", UserName);
         connInfo.put( "password", Password);
         if( EncodingParamName.length() != 0 && EncodingValue.length() != 0)
          connInfo.put( EncodingParamName, EncodingValue);
             Connection connection = DriverManager.getConnection( DatabaseURL, connInfo);
         FileInputStream in = new FileInputStream( SQLFile);
         byte[] buffer = new byte[in.available()];
         in.read( buffer);
         in.close();
         String SQL = new String( buffer);
             PreparedStatement statement = connection.prepareStatement( SQL);
         Date d1 = new Date();
             System.out.println( "Database connected at " + d1 + " Executing statement...");
            ResultSet resultSet = null;
         if( statement.execute())
          resultSet = statement.getResultSet();
         else{
              System.out.println( "Script updates " + statement.getUpdateCount() + " records.");
          System.exit( 0);
             ResultSetMetaData metaData = resultSet.getMetaData();
             BufferedOutputStream out = new BufferedOutputStream( new FileOutputStream( OutputFile));
         if( NeedColumnHeaders && metaData.getColumnCount() > 0){
          String head = new String();
          for( int i = 1; i < metaData.getColumnCount(); i++)
              head += metaData.getColumnName( i) + Separator;
          head += metaData.getColumnName( metaData.getColumnCount());
          out.write( head.getBytes( OutputEncoding), 0, head.length());
          out.write( EOL, 0, 2);
         String record = new String();
         while( resultSet.next()){
          record = "";
          for( int i = 1; i < metaData.getColumnCount(); i++)
              record += resultSet.getString( i) + Separator;
          record += resultSet.getString( metaData.getColumnCount());
          if( AfterLastColumnSeparator)
              record += Separator;
          out.write( record.getBytes( OutputEncoding), 0, record.length());
          out.write( EOL, 0, 2);
         out.close();
         Date d2 = new Date();
             System.out.println( "Done at " + d2);
             System.out.println( "Executing time " + new Time( d2.getTime() - d1.getTime() - 10800000));
     catch( ClassNotFoundException e){
             System.out.println( e.toString());
     catch( SQLException e){
             System.out.println( e.toString());
     catch( java.io.IOException e){
             System.out.println( e.toString());
     System.exit( 0);
    public static void main( String args[]){
     if( args.length == 1)
         new JDBCClient( args[0]);
     else
         System.out.println( "Usage JDBCClient <properties_file>");
}JDBCClient.properties ( for Oracle database)
DriverName=oracle.jdbc.driver.OracleDriver
DatabaseURL=jdbc:oracle:thin:@192.168.1.1:1521:test
UserName=test
Password=test
SQLFile=test.sql
OutputFile=test.csv
Separator=*
NeedColumnHeaders=yes
EncodingParamName=
EncodingValue=
OutputEncoding=windows-1251
AfterLastColumnSeparator=yestest.sql
select * from users;

Using a Java Program to execute JavaScript from a website

Okay, let me try and explain as good as I can. I have a program now, that searched through all files and folders in Unix (Solaris machine) and gets the list of files in the bin and sbin folders.
Well, I want to find the version of each of these files from the bin and sbin folders and not all of them have the -v, -V or -version feature (or any others there may be). But, I found this page:
http://sunsolve.sun.com/pub-cgi/fileFingerprints.pl
where if you go to the page I can find an md5 number, place it in the box and click submit to find versions, if available.
My thing is, as I find the number from my java program, I want to be able to open this page, insert in the box (or maybe even call the javascript function) and then submit to get the version numbers. That would mean I could need to get back info from the javascript function.
I hope that explains what I need and hope that someone can help me.
I have found information on the JSObject, but not sure what that means exactly so if someone can explain this:
JSObject win = JSObject.getWindow(this);
JSObject doc = (JSObject) win.getMember("document");
JSObject loc = (JSObject) doc.getMember("location");
String s = (String) loc.getMember("href"); // document.location.href
win.call("f", null);
it would be greatly appreciated. But, this may not even be what I need. I see that the win.call is where I would call the function needed and I am guessing the null could be where I put the number if that is how the function i need works like that. But, what I dont understand is what "document" is and "location". Also, i the "href" the page I put above? I am just lost on that. Hope someone will understand.
Thank again for the help!

Exactly so. Check out the last item - reading and writing to a URL - writing to a URL.
Pulling out the form code from that page:
<FORM METHOD="POST" ENCTYPE="application/x-www-form-urlencoded">
<TEXTAREA NAME="md5list" ROWS=16 COLS=66 MAXLENGTH="33792"></TEXTAREA>
<BR><INPUT TYPE="submit" NAME="submit" VALUE="submit">
<INPUT TYPE="reset" VALUE="reset">
</FORM>You should end up with something like this (copying and pasting from the example):
URL url = new URL("http://http://sunsolve.sun.com/pub-cgi/fileFingerprints.pl");
String sNumbers = "put your serial nos in this string"
URLConnection connection = url.openConnection();
connection.setDoOutput(true);
PrintWriter out = new PrintWriter(connection.getOutputStream());
out.println("md5list=" + sNumbers);
out.close();
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String inputLine;
while ((inputLine = in.readLine()) != null){
// read in the HTML page result for later parsing?
in.close();

How my java-program invoke Delphi's program or EXE

Hi All, My java program needs to invoke Delphi's program/EXE, but i donn't know how to do.
Pls help!

The following code will open a IE browser rightly,
=====================
try
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("cmd /c start D:\IEXPLORE.EXE"");
InputStream stderr = proc.getErrorStream();
InputStreamReader isr = new InputStreamReader(stderr);
BufferedReader br = new BufferedReader(isr);
String line = null;
System.out.println("<ERROR>");
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System.out.println(line);
System.out.println("</ERROR>");
int exitVal = proc.waitFor();
System.out.println("Process exitValue: " + exitVal);
} catch (Exception ioe){
ioe.printStackTrace();
=====================

How a java program accessable by another java program?

Dear all,
Iam had developed a program which talks to serial port. This program should be intergrated with another main java program . I don't want a function (subroutine )call to my program. i want any other methods to access my program by main java program , which should be fast.

You could serach for "interprocess communication". The main techniques available are pipes and share memory. This means that the two Java programs run as totally separated processes.
An easier way is to restructure the "serial port talking" program into a "utility package with an API" and integrate it with the "main" program. You could let the "serial port talker" run in it's own thread thus creating an illusion of total independency from "main".

How a java program talk to VB6.0 program and exchange files??

Hi, all friends,
I just got a project that ask for make two programs, one using vb6.0 and another one using java. These two programs will communicate and exchange files. It sounds strange. Can I use corba? if so, can any one give me the details of step by step. Or some other solutions. Thanks in advance.

I do not know why you are stuck with such a architecture but i am sure is that this is not a pleasant situation. VB and java are way apart.
Anyway given with the situation and assuming that you just want to exchange files (not variable or inter method calls)..
Solution 1) Fix up two different directories for Java and VB application. And Each application puts files on the other directory when it wants to exhange files. Respective applications keep checking their directories for new files and its kicks of its processing once it finds a new file.
Your exchange file contains all the detials in the agreed format. The new files are loaded in the application and it gets all the details of what it needs to do.
(WITH SOLUTION 2 to 4 you can make inter method calls)
Solution 2) Look into JNI(Java Native interface) through which Java can call a native method in a DLL. That dll is loaded inside the JVM and executed. The dll can also call Java method. And the DLL can communicate to the VB Applicaiton through remote method call or COM interface.
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Solution 4) There are a few Java to COM bridge available in the market. Write a com object with VB and iteract between the Java code and the COM Code.
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How can Java program convert to .exe file which can run on window system?

Hi,
I am a new programmer, now I wrote a program on the Eclipse, and now I want to convert to .exe file and make the program can be run on other window office system PC.
I had downed EXE4J software to make the program to .exe. BUT the exe file can not be run on other PC with the error message that warning the PC have not set up JVE. IS it necessary to set up JVE?
OR give me your experience on how to do it?
Thanks!

>
I am a new programmer, now I wrote a program on the Eclipse, and now I want to convert to .exe file and make the program can be run on other window office system PC.>If you only code for Windows, why not use dotNet or C# or whatever system MS is pushing at this instant?
If you wish to code for computers, Java is good, but it needs a JRE.
The easiest way to get a Java application up and running on a client PC is to launch it via. webstart, and to use deployJava.js to ensure the minimum Java is on the client PC, ready to use webstart.
Used this way, you link to a web page where the user clicks a link that downloads and installs the application (and adds extras like splash screens, desktop integration, registration of interest in file types, automatic update..).
As an aside. The best way to ensure answers is to indicate your interest in solutions, by adding a lot of Duke stars to a thread.

How can my java program launch other applications?

can anyone link me, provide some keywords, or information on how a java program can execute another program... for example, a button click would launch acrobat, firefox, or (in particular) another java application.

don't read all that much fantasy.
I've read Eddings' Belgariad and Malloreon, which I really liked at the time but which are not even in the same league as GRRM. The characters are much more one-dimensional, and the plot gets cornier as you go along.
IVE READ BELGARIOD... AGREE THAT IT WAS PRETTY SHALLOW AND I READ IT AFTER LOTR SO IT WAS SUCH A PALE RIPOFF IN COMPARISON
His Elenium and Tamuli series were a little better, but still far from Ice and Fire.
Tolkein, of course, but you've probably heard of him. :-)
Donaldson's Mirror of Her Dreams and A Man Rides through were good.
HAVENT READ THESE, WILL ADD TO MY LIST, THANKS!
Terry Brooks' Shanara series is supposed to be pretty good, and I think Anne McCaffery's Dragonriders of Pern series is considered to be among the classics, but I've never read either one.
READ SOME BROOKS AND FOUND IT SHALLOW LIKE EDDINGS. HAVE READ MCCAFFERY BUT NOT DRAGONRIDERS, AND THE TRILOGY I READ WAS OK BUT THE TONE WAS REALLY GOOFY. A GROUP OF REFUGES ON A NEW PLANET AT A TIME WHEN THE HUMAN RACE IS ENSLAVED BY ALIENS, AND THE BOOK SEEMED TO FOCUS ON HOW FUN BUILDING A CAMP WAS ON THE NEW PLANET AND EVERYONE WAS REALLY PEPPY WHICH FELT ODD GIVEN THE CIRCUMSTANCES OF THE SETTING.
Michael Moorcock's Elric series was very good, also very dark. It was kind of... I don't know... odd. Like you'd want to light up a bong and put on some Floyd while reading it.
HAVENT READ EITHER, ANOTHER FOR THE LIST, THANKS AGAIN!
There's another series of 2 or 3 books that I read a few years ago and really liked, but I can't for the life of me remember the author, the books, any characters names...
P.S. If you want to talk about a nag of a female character, you gotta love (as in hate) Cersei. She gets her on POV in Feast. Good stuff.
YEAH I LIKE CERSEI ACTUALLY. GRRM IS GOOD IN HOW THERE REALLY IS NO MAIN CHARACTER AND EVERYONE IS VERY EXCITING TO READ. RJ ON THE OTHERHAND HAS A DEFINATE CENTRAL CHARACTER TO THE PLOT, AND CHAPTER AFTER CHAPTER OF SOME OF THE FEMALE POV'S GOT AGGRAVATING ESPECIALLY WHEN THEY NAG SO MUCH THE TRUER HEROS OF THE STORY (MY OPINION)... ITS LIKE, SHUT YOUR MOUTH AND LET THEM SAVE THE DAY ALREADY... HEHE... BUT YOU'LL SEE OR HAVE A DIFFERENT OPINION ENTIRELY.
to you i recommend orson scott card... you've probably read ender's game but he has some really good fantasy too... the homecoming series (first book call of earth or memory of earth) was really good, and the alvin maker series is ok plotwise but the characters are incredible... i found a lot of humor and witty dialog in that series and enjoyed it immensely. anyways, thanks again for the list additions, will read feast of crows first, hopefully soon. glad to hear you're liking it... some reviews on amazon weren't stellar.

How to execute an external executable in my java program?

hi,
i want to write a java program to execute some external executables.
for example, i had an executable which takes a string as its input parameter, and:
it writes to stdout a string : "[stdout] hello, "+parameter+"!";
it writes to stderr a string : "[stderr] hello, "+parameter+"!".
and it exits with an error code 1.
my java program looks like this:
public class Test {
public static void main(String[] args)
throws Exception {
    String inputParameter = "heavyz";
    String stdoutOutput = null;
    String stderrOutput = null;
    int exitCode;
    // Do something here to launch the executable,
    // providing inputParameter as its input,
    // getting its stdout output to String stdoutOutput,
    // and its stderr output to String stderrOutput,
    // and its exit code to int exitCode.
    return;
}anybody can help me to complete the program above?
thanks a lot.
heavy ZHENG

check out Runtime.getRuntime().exec();

Executing Java Programs Without BlueJ

I've created a program that includes a number of classes. I want to be able to pass it along to someone who doesn't have BlueJ installed on his computer. How can the program be executed or started from the command line prompt? In BlueJ, I create an object of a particular class and the rest is done within the methods of that class. (These methods are called in the constructor.) I added the following line to that main class:
public static void main (String [ ] args)But I'm not sure what to put in that method. I'm also not sure of the exact command to enter in the command line prompt to get the ball rolling. Help?
Any suggestions or helpful comments would be greatly appreciated!
Thanks,
Erica

This example may help:
public class HelloWorld {
    // Constructor does stuff
    public HelloWorld() {
        System.out.println("Hello World");
        // do other stuff
    // main method just creates a new HelloWorld object
    // the JVM exits when main returns
    // i.e. when the constructor returns in this case
    public static void main(String[] args) {
        new HelloWorld();
}On the command line all you need to do is compile HelloWorld.java so that you end up with HelloWorld.class. Then do the following (in the same directory as the class file):
java HelloWorldThat's it. Of course I'm not sure if BlueJ provides other non-standard libraries which may need to be in your classpath. That's a whole other issue.
John

How Can we stop the execution of java program which contain infinite loop

Dear All,
I create one .bat file which which execute the simple java program
I write one java program which execute above .bat file using instance of Runtime Class of java
It's work fine if java program which is executed by .bat file is simple(Which has normal termination)
But if that program contain inifinte loop then that file will goes on executing untill I close it manually
So i want a solution in java which close that bat file (command window ) which is in running condtion
If there any solution please replay me
I try to close that .bat file using destroy() ,stop() method of Process and Runtime , Thread Class
but it did not give me correct output
.bat file still running !!!!!!!!!
Thanks in advance

Why not use javaw.exe to make the app run so you don't need the dos window (which is presumably what you are actually talking about when you say bat file).

Executing UD32 from a Java program

Hi I have Clarify application istalled with Tuxedo6.4. I was able to use UD32 utility
from commandline and execute services in tuxedo. On the Unix (Sun Solaris 2.6)
I am using the following to execute the UD32
$ud32 -U sa<NL>
SRVCNM<TAB>CB_EXESUB<NL>
CLFY_SUB<TAB>ExternalMsg<NL>
EQUIP_ID<TAB>1<NL>
<NL>
however if I use a java program to execute from the same directory, it is not
working. I am obtaining a process from the runtime and writting to the process
to get the above. My code is as follows
import java.io.*;
public class udexec {
public static void main(String args[]) {
try{
Runtime rt = Runtime.getRuntime();
System.out.println("Before");
Process prcs = rt.exec("ud32 -U sa\n");
System.out.println("After: " + prcs);
InputStreamReader isr = new InputStreamReader(prcs.getInputStream());
PrintWriter out = new PrintWriter(prcs.getOutputStream());
out.println("SRVCNM CB_EXESUB");
out.println("CLFY_SUB ExternalMsg");
out.println("EQUIPID 1");
out.println("");
int ret = isr.read();
String line;
System.out.println("Before Print");
System.out.println(ret);
catch (Exception e) { System.out.println(e); }
Any help will be greatly appreciated.
Thank You
Raju

No actually I am not getting any error messages. If I use from Command line, I
can see the output in one of the stdout files. In tha case of java I am not getting
any. I think after the first line (ud32 -U sa), writing to the process in java
is not working. Atleast thats what I am thinking.
--Raju
Peter Holditch <[email protected]> wrote:
Raju,
In what way is it failing? Is there any error writtem to stderr of the
ud process, or to
the ULOG?
Regards,
Peter.
Raju Vatsavayi wrote:
Hi I have Clarify application istalled with Tuxedo6.4. I was able touse UD32 utility
from commandline and execute services in tuxedo. On the Unix (Sun Solaris2.6)
I am using the following to execute the UD32
$ud32 -U sa<NL>
SRVCNM<TAB>CB_EXESUB<NL>
CLFY_SUB<TAB>ExternalMsg<NL>
EQUIP_ID<TAB>1<NL>
<NL>
however if I use a java program to execute from the same directory,it is not
working. I am obtaining a process from the runtime and writting tothe process
to get the above. My code is as follows
import java.io.*;
public class udexec {
public static void main(String args[]) {
try{
Runtime rt = Runtime.getRuntime();
System.out.println("Before");
Process prcs = rt.exec("ud32 -U sa\n");
System.out.println("After: " + prcs);
InputStreamReader isr = new InputStreamReader(prcs.getInputStream());
PrintWriter out = new PrintWriter(prcs.getOutputStream());
out.println("SRVCNM CB_EXESUB");
out.println("CLFY_SUB ExternalMsg");
out.println("EQUIPID 1");
out.println("");
int ret = isr.read();
String line;
System.out.println("Before Print");
System.out.println(ret);
catch (Exception e) { System.out.println(e); }
Any help will be greatly appreciated.
Thank You
Raju

How a java program is executed ?

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