NullPointerException Error with JPanel and CardLayout

Question

I am working on hotel management software for class and I am running into a few issues with my code. At this point, I am simply trying to add a JPanel I created in a separate cl

Answer 1

jpanel.add("Room", room.getRoomPanel());

You've never initialized room

RoomSystem room;

Even if you do initialize it RoomSystem room = new RoomSystem(), you still have another problem in your RoomSystem class. You have shadowed roomPanel, and therefore the class member is null, when you try and call getRoomPanel(). In your constructor, change

// shadowing the class field roomPanel
JPanel roomPanel = new JPanel(new FlowLayout());  

to 

roomPanel = new JPanel(new FlowLayout());