JPanel和CardLayout出现NullPointerException错误

JPanel和CardLayout出现NullPointerException错误

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

您从未初始化

room

RoomSystem room;

即使您确实对其进行了初始化

RoomSystem room = newRoomSystem()

，您的

RoomSystem

班级仍然还有另一个问题。您已经遮蔽了阴影

roomPanel

，因此在尝试调用时，类成员为null

getRoomPanel()

。在您的构造函数中，更改

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