SayOneAndTwo.java

public class SayOneAndTwo implements start.DoOneAndTwo {
  public void doOne() {
    System.out.println("Say one");
  }

  public void doTwo() {
    System.out.println("Say two");
  }
}

start.java

public class start {
  public static void main(String[] args) throws Exception {
    DoOneAndTwo program = (DoOneAndTwo) Class.forName(args[0]).newInstance();
    program.doOne();
    program.doTwo();
  }
  public interface DoOneAndTwo {
    void doOne();
    void doTwo();
  }
}

the command

java start SayOneAndTwo