Why we use JPanel

JPanel we will help java programmer to create more complex graphical user interface. But how ? It answer is, it allow other component to add into it. Component that i mean here like JButton, JLabel or JTextField or others. It also give ability to other JPanel add into it. For example, we has two JPanel called panelA and panelB. We can add panelA into panelB. So, if panelA also contains other components and panelB also contains other component beside panelA that we add before, how complex the graphical user interface...i hope you can imagine it.