Need to run a java program within a java program

[peterdfl]

Hi I need to run a java program within a java program. I need to read the output of the program from a java program, my code keeps giving me the error Array index out of bound java 44.

   public class ExecDemo
    {
        static public String[] runCommand(String cmd) throws IOException
        {  // The actual procedure for process execution:

           // runCommand(String cmd);

            ArrayList list = new ArrayList(); //storing output.

            Process proc = Runtime.getRuntime().exec("File 1.java");
            //Runtime.getRuntime().exec("C:\User\Peter Dormevil\Desktop\Java programs\File1.java");



            InputStream istr = proc.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(istr));
            // Create a [BufferedReader] and specify it reads from an input stream.

            String str; // Temporary String variable
            while ((str = br.readLine()) != null) list.add(str);
            // Read to Temp Variable, Check for [null] then Add to (ArrayList)list

            try { proc.waitFor(); } // Wait for process to terminate and catch any Exceptions.

            catch (InterruptedException e)
			{
	        System.err.println("Process was interrupted"); }

            // Note: proc.exitValue() returns the exit value. (

            br.close(); // Done.

            return (String[])list.toArray(new String[20]);
        }

        public static void main(String args[]) throws IOException
        {
            try
            {
                String outlist[] = runCommand(args[20]);
                for (int i = 0; i < outlist.length; i++)

			System.out.println(outlist[i]);
                // Print the output to screen character by character.
                // Safe and not very inefficient.
            }
            catch (IOException e)
            {
				System.err.println(e);

				}
        }
    }

[neilcoffey]

You're referring to args[20], which means the 21st argument. I'm guessing you didn't mean that, and aren't passing in 21 arguments to the program.

A possibly more serious problem with this program is that whenever you call a subprocess, you must drain both output stream and error stream. Consider: reading both streams (from separate threads), or using a ProcessBuilder and calling redirectErrorStream() on it to merge the output and error streams.

[Eranga]

How you handle 20 command line parameters there?