Calling one Java Prog from another - Code

[madhesh raj]

Hi,
I wrote a Hello World Java program and tried to invoke it from another program.
public class RunExample
{
public static void main(String []args)
{
Runtime rtime = Runtime.getRuntime();
try
{
rtime.exec("java HelloWorld");
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
The program compiles fine. The path and class path are set properly. But when i execute it, the second program (i.e. HelloWorld) does not print the output -- HelloWorld on the screen.
What could be wrong?
Madhesh

[NageswaraRao Karra]

Hello!
change like this
import java.io.*
_______________
Process p=rtime.exec("java HelloWorld");
use p.getInputStream() method
read from InputStream till it is empty
Print it on to the System.out with the help of OutputStream
____________________________
hope this is what you wanted

[Frank Carver]

Or alternatively run it directly in the same VM as your other program:

public class RunExample
{
   public static void main(String []args)
   {
      HelloWord.main(new String[0]);
    }
 }

Is this what you want?

[madhesh raj]

Hi Frank,
Thanks for the suggestion. I could not get what the new String[0] does. Is it to pass the arguments to the called program? (in this case HelloWorld)?
IF not, Supposing i want to pass some arguments to the second program what do i need to do? Can i just form my own String array of arguments and pass it.
Regards
Madhesh

[Jim Yingst]

The main() method expects a String[] argument of some sort. The new String[0] creates a zero-length array of Strings - it's a way of saying "here's the list of arguments - there aren't any". Alternately you could pass null instead - as long as HelloWorld.main() does not attempt to use the args variable, there's no problem.
If you do want to pass arguments to HelloWorld.main(), then yes, you would need to create a non-empty String array to hold the arguments. E.g.
<code><pre> String[] myArgs = {"first arg", "second arg"};
HelloWorld.main(myArgs);</pre></code>

[madhesh raj]

Hi,
Does reading from the process's InputStream work the other way round also. That is, suppose the process is expecting some keyboard input from user then can i map it using the the process's OutputStream?
Pls give a sample code. It would be really useful
Madhesh