Parar Processo - Runtime.getRuntime().exec

public class RunExec extends JFrame implements ActionListener {

private static final long serialVersionUID = 1L;
  private JButton btnAtivaProg = new JButton("Run...");
  private JButton btnClose = new JButton("Sair");
  private Process pc;

  public RunExec(){
    super("Executa Aplicações");

    btnAtivaProg.addActionListener(this);
    btnClose.addActionListener(this);
	
    this.getContentPane().setLayout(new GridLayout(1,1));
    this.getContentPane().add(btnAtivaProg);
    this.getContentPane().add(btnClose);
		
    this.setBounds(10,10,200,100);
    this.setVisible(true);				
  }
	
  public static void main(String[] args) throws Exception{
    new RunExec();
  }

  public void actionPerformed(ActionEvent ev) {
    if (ev.getSource() == btnAtivaProg){
      try {
        pc = Runtime.getRuntime().exec("notepad.exe c:/boot.ini");
      } catch (IOException e) {}
    } else if (ev.getSource() == btnClose){
      if (pc != null) pc.destroy();
      System.exit(0);
    }		
  }
	
}