You can capture the output of an external program using the logic shown below:

 import java.io.*;

public class CmdExec {
  public CmdExec(String cmdline) {
    try {
     String line;
     Process p = Runtime.getRuntime().exec(cmdline);
     BufferedReader input = 
       new BufferedReader
         (new InputStreamReader(p.getInputStream()));
     while ((line = input.readLine()) != null) {
       System.out.println(line);
       }
     input.close();
     } 
    catch (Exception err) {
     err.printStackTrace();
     }
   }

public static void main(String argv[]) {
  new CmdExec("myprog.bat");
  }
}
  [myprog.bat]
   echo hello world!