For Frame objects, f, can directly use the layout. The next (f) to achieve paging capabilities;
But for jf JFrame object, if use layout directly. The next (jf) will direct error, must change to layout. The next (jf) getContentpane ()) to normal page

Excuse me, what is the difference between both? I tried the Frame object is not getContentpane method, but why not say not clear, please, trust, thank you!