title: JFrame inside another JFrame
body: <p>I have a game of chess.
  I have written 3 classes.
  1st if for game. (chessboard, pieces, and so on)
  And another one is for menu. (buttons like new, open, set time)</p>
  
  <p>Both of them use JFrame.</p>
  
  <p>I would like to put both classes mentioned above into the 3rd class. For example the Game window would be on the left, and the menu on the right.
  The third class would also show the whole app by JFrame.</p>
  
  <p>How to do that?</p>