public void actionPerformed( ActionEvent e )
	 {
	     String username = textFieldId.getText();
	     String password = String.valueOf(textFieldPassword.getPassword()); //transfer char[] type to String
	    
		if(e.getSource() == btnShowReservationCard)
		{
			cardManager = (CardLayout) pnlCardDeck.getLayout();
			cardManager.show(pnlCardDeck, (String)"Reservation");
			
		}else if (e.getSource()== btnShowCustomerCard)
		{
			cardManager = (CardLayout) pnlCardDeck.getLayout();
			cardManager.show(pnlCardDeck, (String)"Customer");
			
		}else if (e.getSource()== btnShowServiceCard)
		{
			cardManager = (CardLayout) pnlCardDeck.getLayout();
			cardManager.show(pnlCardDeck, (String)"Service");
		}else if (e.getSource()== btnShowMgtCard)
		{
			cardManager = (CardLayout) pnlCardDeck.getLayout();
			cardManager.show(pnlCardDeck, (String)"Management");
		}
	    
	     
	     if ( e.getSource() == btnLogin )    
				 if( !username.isEmpty() && !password.isEmpty() && loginValidation(username,password) == true)
				 {
					JOptionPane.showMessageDialog(this, "Login Success!");
					cardManager = (CardLayout) mainPane.getLayout();
					cardManager.show(mainPane, (String)"Menu");
				 }
				 else
				 {	
					  JOptionPane.showMessageDialog(this, "Invalid ID or Password. Please Try again.", "Login Failed",
			                    JOptionPane.ERROR_MESSAGE);
				 } 	
	     	textFieldId.setText("");
			textFieldPassword.setText("");
			 
	   }