Launching Java Application From A Java Application

Question

Hello,
I am building a compiler and would like to have run feature. The problem is I can not seem to figure out the righ syntax to run and application from my java application.
Here is the code I am using to run an application:
public void RunClass()
try
Runtime rtr=Runtime.getRuntime();
Process pr = rtr.exec("java " + CurrentDirectory + FileNoExt);
String line;
BufferedReader rerr = new BufferedReader(new InputStreamReader(pr.getErrorStream()));
if((line = rerr.readLine()) == null) { CompileMessageArea.setText("Program Running\n"); }
while ((line = rerr.readLine()) != null) { CompileMessageArea.append(line +"\n"); }
rerr.close();
catch(Exception re) { re.printStackTrace(); }
The following is an example of what the above would send to the:
java c:\MyJava\Programs\test
If you try to type something like that in a DOS prompt it will not work. You must first change to that directory, but I am hoping there is an easy way to change the syntax. On the other hand if you want to compile a program you can type:
javac c:\MyJava\Programs\test.java
and it will work just fine. This is kind of funny and I use this syntax for my compiler in my program. You would think that the same syntax would work the same for both compiling and running but it does not. So, I know that if I just know what the correct syntax that dos would except for running an application it would work.
So, if you have the answer for me PLEASE LET ME KNOW.
It is easily testable by keying it into the dos prompt.
Sincerely,
Eric Kohr

Answer 1

If you want to do it that way you need to use the environment parameter of the exec() method. Use it to set your classpath to the directory that's need for the java application you are about to run... for instance.
String[] env = new String[] {"CLASSPATH=c:\classes"}
String command = "java somePackage.someProgram";
Runtime.getRuntime().exec( env, command);Where your program is in the file "c:\classes\somePackage\someProgram"
your mileage may vary :)
You can also reflectively load classes into the running VM and invoke their main methods. This give you the ablility to control them a bit more.