JFrame extends Frame that extends Window that extends Container - Component - Object. Not JComponent. JComponent is a subclass from Container, and not associated with JFrame in any way. Subclasses of JComponent is:
Code:
AbstractButton, BasicInternalFrameTitlePane, JColorChooser,
JComboBox, JFileChooser, JInternalFrame,
JInternalFrame.JDesktopIcon, JLabel, JLayeredPane, JList,
JMenuBar, JOptionPane, JPanel, JPopupMenu, JProgressBar,
JRootPane, JScrollBar, JScrollPane, JSeparator, JSlider, JSplitPane,
JTabbedPane, JTable, JTableHeader, JTextComponent, JToolBar,
JToolTip, JTree, JViewport
Therefore JFrame, doesn't have setDoubleBuffered as method.