如何让JComboBox自动更新？

I'm struggling with update my item in JComboBox. When I load item from a file, the combobox display properly, however when I tried to add or remove item from combobox item, the combobox doesn't update automatically, it still remain the same item instead. Here is my code This is where I load the combobox itemI'm struggling with update my item in JComboBox