Running a java program from another java program

I am working on a simple java program. It simply compiles and executes another java program. I am using Runtime.exec() function to compile and run. There is no problem with compilation. but when it runs, if the second program needs an input to read from keyboard, I can't give it from the master process. I used getOutputStream() function. but it couldn't help. I will provide my code.

public class sam {  
    public static void main(String[] args) throws Exception {  
        try { 
             Process p = Runtime.getRuntime().exec("javac sam2.java");
             Process p2 = Runtime.getRuntime().exec("java sam2");
             BufferedReader in = new BufferedReader(  
                                new InputStreamReader(p2.getInputStream()));

             OutputStream out = p.getOutputStream();
             String line = null; 
             line = in.readLine();
             System.out.println(line);
             input=input+"\n";
             out.write(input.getBytes());
             p.wait(10000);
             out.flush();
        }catch (IOException e) {  
             e.printStackTrace();  
        }  
    }  
}  

This is my master program(sam.java).

The following is the code of sam2.java

public class sam2 {  
public static void main(String[] args) throws Exception {  

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String str; 
    System.out.println("Enter the number..\n");
    str = br.readLine(); 
    System.out.println(Integer.parseInt(str));

    }  
}  

There is no problem, if my second program has only printing statements. But the problem arises when I have to read something from the other.

It is a bit strange but you can run the second program without forking it. Just calling the main method in it. So forget the runtime section and do this:

sam2.main(new String[0]);

Of course this way you must compile sam2 at compile time