question: @ Override public Dimension preferredLayoutSize ( Container parent ) { Dimension rd , mbd ; Insets i = rootPane . getInsets ( ) ; Container contentPane = rootPane . getContentPane ( ) ; JMenuBar menuBar = rootPane . getJMenuBar ( ) ; if ( contentPane . isVisible ( ) ) { rd = contentPane . getPreferredSize ( ) ; } else { rd = new Dimension ( 0 , contentPane . getPreferredSize ( ) . height ) ; } if ( menuBar != null && menuBar . isVisible ( ) ) { mbd = menuBar . getPreferredSize ( ) ; } else { mbd = new Dimension ( 0 , 0 ) ; } return new Dimension ( Math . max ( rd . width , mbd . width ) + i . left + i . right , rd . height + mbd . height + i . top + i . bottom ) ; }
target:  Returns the amount of space the layout would like to have.