java에서 cmd 실행하기

import java.io.*;

class runTest{

 public static void main(String a[]) {

  String cmd = "java";
  Process p = null;
  String returnData = "";
  try {
     p = Runtime.getRuntime().exec(cmd);
     InputStream in = p.getInputStream(); // Ȥ getErrorStream
     int i;
     while ((i=in.read()) != -1) {
    returnData += (char)i;
    }
    System.out.println(returnData);
  } catch (IOException e) { e.printStackTrace(); }
 }
}