20. CardLayout navigation

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      private CardLayout mLayout; // class member
  
      // constructor
      JPanel cards = new JPanel(); // panel to hold cards
      mLayout = new CardLayout();
      cards.setLayout( mLayout );
  
      // operations
      mLayout.first( cards );
      mLayout.previous( cards );
      mLayout.next( cards );
      mLayout.last( cards );