javax.swing.plaf.basic

## Class BasicComboPopup

- java.lang.Object
- - java.awt.Component
  - - java.awt.Container
    - - javax.swing.JComponent
      - - javax.swing.JPopupMenu
        - - javax.swing.plaf.basic.BasicComboPopup

- All Implemented Interfaces:
    ImageObserver, MenuContainer, Serializable, Accessible, MenuElement, ComboPopup
  Direct Known Subclasses:
    MetalComboBoxUI.MetalComboPopup

      public class BasicComboPopup
      extends JPopupMenu
      implements ComboPopup

  This is a basic implementation of the `ComboPopup` interface. This class represents the ui for the popup portion of the combo box.

  All event handling is handled by listener classes created with the `createxxxListener()` methods and internal classes. You can change the behavior of this class by overriding the `createxxxListener()` methods and supplying your own event listeners or subclassing from the ones supplied in this class.

  Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeansTM has been added to the `java.beans` package. Please see `XMLEncoder`.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `class` | `BasicComboPopup.InvocationKeyHandler` As of Java 2 platform v 1.4, this class is now obsolete and is only included for backwards API compatibility.
    `protected class` | `BasicComboPopup.InvocationMouseHandler` A listener to be registered upon the combo box (not its popup menu) to handle mouse events that affect the state of the popup menu.
    `protected class` | `BasicComboPopup.InvocationMouseMotionHandler` This listener watches for dragging and updates the current selection in the list if it is dragging over the list.
    `protected class` | `BasicComboPopup.ItemHandler` This listener watches for changes to the selection in the combo box.
    `class` | `BasicComboPopup.ListDataHandler` As of 1.4, this class is now obsolete, doesn't do anything, and is only included for backwards API compatibility.
    `protected class` | `BasicComboPopup.ListMouseHandler` This listener hides the popup when the mouse is released in the list.
    `protected class` | `BasicComboPopup.ListMouseMotionHandler` This listener changes the selected item as you move the mouse over the list.
    `protected class` | `BasicComboPopup.ListSelectionHandler` As of Java 2 platform v 1.4, this class is now obsolete, doesn't do anything, and is only included for backwards API compatibility.
    `protected class` | `BasicComboPopup.PropertyChangeHandler` This listener watches for bound properties that have changed in the combo box.

    - ### Nested classes/interfaces inherited from class javax.swing.JPopupMenu

      `JPopupMenu.AccessibleJPopupMenu, JPopupMenu.Separator`

    - ### Nested classes/interfaces inherited from class javax.swing.JComponent

      `JComponent.AccessibleJComponent`

    - ### Nested classes/interfaces inherited from class java.awt.Container

      `Container.AccessibleAWTContainer`

    - ### Nested classes/interfaces inherited from class java.awt.Component

      `Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected Timer` | `autoscrollTimer` This protected field is implementation specific.
    `protected JComboBox` | `comboBox`
    `protected boolean` | `hasEntered`
    `protected boolean` | `isAutoScrolling`
    `protected ItemListener` | `itemListener` This protected field is implementation specific.
    `protected KeyListener` | `keyListener` This protected field is implementation specific.
    `protected JList` | `list` This protected field is implementation specific.
    `protected ListDataListener` | `listDataListener` This protected field is implementation specific.
    `protected MouseListener` | `listMouseListener` This protected field is implementation specific.
    `protected MouseMotionListener` | `listMouseMotionListener` This protected field is implementation specific.
    `protected ListSelectionListener` | `listSelectionListener` This protected field is implementation specific.
    `protected MouseListener` | `mouseListener` This protected field is implementation specific.
    `protected MouseMotionListener` | `mouseMotionListener` This protected field is implementation specific.
    `protected PropertyChangeListener` | `propertyChangeListener` This protected field is implementation specific.
    `protected static int` | `SCROLL_DOWN`
    `protected static int` | `SCROLL_UP`
    `protected int` | `scrollDirection`
    `protected JScrollPane` | `scroller` This protected field is implementation specific.
    `protected boolean` | `valueIsAdjusting` As of Java 2 platform v1.4 this previously undocumented field is no longer used.

    - ### Fields inherited from class javax.swing.JComponent

      `accessibleContext, listenerList, TOOL_TIP_TEXT_KEY, ui, UNDEFINED_CONDITION, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, WHEN_FOCUSED, WHEN_IN_FOCUSED_WINDOW`

    - ### Fields inherited from class java.awt.Component

      `BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT`

    - ### Fields inherited from interface java.awt.image.ImageObserver

      `ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `BasicComboPopup(JComboBox combo)`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `autoScrollDown()` This protected method is implementation specific and should be private.
    `protected void` | `autoScrollUp()` This protected method is implementation specific and should be private.
    `protected Rectangle` | `computePopupBounds(int px, int py, int pw, int ph)` Calculate the placement and size of the popup portion of the combo box based on the combo box location and the enclosing screen bounds.
    `protected void` | `configureList()` Configures the list which is used to hold the combo box items in the popup.
    `protected void` | `configurePopup()` Configures the popup portion of the combo box.
    `protected void` | `configureScroller()` Configures the scrollable portion which holds the list within the combo box popup.
    `protected MouseEvent` | `convertMouseEvent(MouseEvent e)`
    `protected ItemListener` | `createItemListener()` Creates an `ItemListener` which will be added to the combo box.
    `protected KeyListener` | `createKeyListener()` Creates the key listener that will be added to the combo box.
    `protected JList` | `createList()` Creates the JList used in the popup to display the items in the combo box model.
    `protected ListDataListener` | `createListDataListener()` Creates a list data listener which will be added to the `ComboBoxModel`.
    `protected MouseListener` | `createListMouseListener()` Creates a mouse listener that watches for mouse events in the popup's list.
    `protected MouseMotionListener` | `createListMouseMotionListener()` Creates a mouse motion listener that watches for mouse motion events in the popup's list.
    `protected ListSelectionListener` | `createListSelectionListener()` Creates a list selection listener that watches for selection changes in the popup's list.
    `protected MouseListener` | `createMouseListener()` Creates a listener that will watch for mouse-press and release events on the combo box.
    `protected MouseMotionListener` | `createMouseMotionListener()` Creates the mouse motion listener which will be added to the combo box.
    `protected PropertyChangeListener` | `createPropertyChangeListener()` Creates a `PropertyChangeListener` which will be added to the combo box.
    `protected JScrollPane` | `createScroller()` Creates the scroll pane which houses the scrollable list.
    `protected void` | `delegateFocus(MouseEvent e)` This is is a utility method that helps event handlers figure out where to send the focus when the popup is brought up.
    `protected void` | `firePopupMenuCanceled()` Notifies `PopupMenuListeners` that this popup menu is cancelled.
    `protected void` | `firePopupMenuWillBecomeInvisible()` Notifies `PopupMenuListener`s that this popup menu will become invisible.
    `protected void` | `firePopupMenuWillBecomeVisible()` Notifies `PopupMenuListener`s that this popup menu will become visible.
    `AccessibleContext` | `getAccessibleContext()` Gets the AccessibleContext associated with this BasicComboPopup.
    `KeyListener` | `getKeyListener()` Implementation of ComboPopup.getKeyListener().
    `JList` | `getList()` Implementation of ComboPopup.getList().
    `MouseListener` | `getMouseListener()` Implementation of ComboPopup.getMouseListener().
    `MouseMotionListener` | `getMouseMotionListener()` Implementation of ComboPopup.getMouseMotionListener().
    `protected int` | `getPopupHeightForRowCount(int maxRowCount)` Retrieves the height of the popup based on the current ListCellRenderer and the maximum row count.
    `void` | `hide()` Implementation of ComboPopup.hide().
    `protected void` | `installComboBoxListeners()` This method adds the necessary listeners to the JComboBox.
    `protected void` | `installComboBoxModelListeners(ComboBoxModel model)` Installs the listeners on the combo box model.
    `protected void` | `installKeyboardActions()`
    `protected void` | `installListListeners()` Adds the listeners to the list control.
    `boolean` | `isFocusTraversable()` Overridden to unconditionally return false.
    `void` | `show()` Implementation of ComboPopup.show().
    `protected void` | `startAutoScrolling(int direction)` This protected method is implementation specific and should be private.
    `protected void` | `stopAutoScrolling()` This protected method is implementation specific and should be private.
    `protected void` | `togglePopup()` Makes the popup visible if it is hidden and makes it hidden if it is visible.
    `protected void` | `uninstallComboBoxModelListeners(ComboBoxModel model)` Removes the listeners from the combo box model
    `void` | `uninstallingUI()` Called when the UI is uninstalling.
    `protected void` | `uninstallKeyboardActions()`
    `protected void` | `updateListBoxSelectionForEvent(MouseEvent anEvent, boolean shouldScroll)` A utility method used by the event listeners.

    - ### Methods inherited from class javax.swing.JPopupMenu

      `add, add, add, addMenuKeyListener, addPopupMenuListener, addSeparator, createActionChangeListener, createActionComponent, getComponent, getComponentAtIndex, getComponentIndex, getDefaultLightWeightPopupEnabled, getInvoker, getLabel, getMargin, getMenuKeyListeners, getPopupMenuListeners, getSelectionModel, getSubElements, getUI, getUIClassID, insert, insert, isBorderPainted, isLightWeightPopupEnabled, isPopupTrigger, isVisible, menuSelectionChanged, pack, paintBorder, paramString, processFocusEvent, processKeyEvent, processKeyEvent, processMouseEvent, remove, removeMenuKeyListener, removePopupMenuListener, setBorderPainted, setDefaultLightWeightPopupEnabled, setInvoker, setLabel, setLightWeightPopupEnabled, setLocation, setPopupSize, setPopupSize, setSelected, setSelectionModel, setUI, setVisible, show, updateUI`

    - ### Methods inherited from class javax.swing.JComponent

      `addAncestorListener, addNotify, addVetoableChangeListener, computeVisibleRect, contains, createToolTip, disable, enable, firePropertyChange, firePropertyChange, firePropertyChange, fireVetoableChange, getActionForKeyStroke, getActionMap, getAlignmentX, getAlignmentY, getAncestorListeners, getAutoscrolls, getBaseline, getBaselineResizeBehavior, getBorder, getBounds, getClientProperty, getComponentGraphics, getComponentPopupMenu, getConditionForKeyStroke, getDebugGraphicsOptions, getDefaultLocale, getFontMetrics, getGraphics, getHeight, getInheritsPopupMenu, getInputMap, getInputMap, getInputVerifier, getInsets, getInsets, getListeners, getLocation, getMaximumSize, getMinimumSize, getNextFocusableComponent, getPopupLocation, getPreferredSize, getRegisteredKeyStrokes, getRootPane, getSize, getToolTipLocation, getToolTipText, getToolTipText, getTopLevelAncestor, getTransferHandler, getVerifyInputWhenFocusTarget, getVetoableChangeListeners, getVisibleRect, getWidth, getX, getY, grabFocus, isDoubleBuffered, isLightweightComponent, isManagingFocus, isOpaque, isOptimizedDrawingEnabled, isPaintingForPrint, isPaintingOrigin, isPaintingTile, isRequestFocusEnabled, isValidateRoot, paint, paintChildren, paintComponent, paintImmediately, paintImmediately, print, printAll, printBorder, printChildren, printComponent, processComponentKeyEvent, processKeyBinding, processMouseEvent, processMouseMotionEvent, putClientProperty, registerKeyboardAction, registerKeyboardAction, removeAncestorListener, removeNotify, removeVetoableChangeListener, repaint, repaint, requestDefaultFocus, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, resetKeyboardActions, reshape, revalidate, scrollRectToVisible, setActionMap, setAlignmentX, setAlignmentY, setAutoscrolls, setBackground, setBorder, setComponentPopupMenu, setDebugGraphicsOptions, setDefaultLocale, setDoubleBuffered, setEnabled, setFocusTraversalKeys, setFont, setForeground, setInheritsPopupMenu, setInputMap, setInputVerifier, setMaximumSize, setMinimumSize, setNextFocusableComponent, setOpaque, setPreferredSize, setRequestFocusEnabled, setToolTipText, setTransferHandler, setUI, setVerifyInputWhenFocusTarget, unregisterKeyboardAction, update`

    - ### Methods inherited from class java.awt.Container

      `add, add, add, add, add, addContainerListener, addImpl, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, countComponents, deliverEvent, doLayout, findComponentAt, findComponentAt, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents, getComponentZOrder, getContainerListeners, getFocusTraversalKeys, getFocusTraversalPolicy, getLayout, getMousePosition, insets, invalidate, isAncestorOf, isFocusCycleRoot, isFocusCycleRoot, isFocusTraversalPolicyProvider, isFocusTraversalPolicySet, layout, list, list, locate, minimumSize, paintComponents, preferredSize, printComponents, processContainerEvent, processEvent, remove, removeAll, removeContainerListener, setComponentZOrder, setFocusCycleRoot, setFocusTraversalPolicy, setFocusTraversalPolicyProvider, setLayout, transferFocusDownCycle, validate, validateTree`

    - ### Methods inherited from class java.awt.Component

      `action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, bounds, checkImage, checkImage, coalesceEvents, contains, createImage, createImage, createVolatileImage, createVolatileImage, disableEvents, dispatchEvent, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getBackground, getBounds, getColorModel, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeysEnabled, getFont, getForeground, getGraphicsConfiguration, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocationOnScreen, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPeer, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getToolkit, getTreeLock, gotFocus, handleEvent, hasFocus, imageUpdate, inside, isBackgroundSet, isCursorSet, isDisplayable, isEnabled, isFocusable, isFocusOwner, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isPreferredSizeSet, isShowing, isValid, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, processComponentEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, resize, resize, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setFocusable, setFocusTraversalKeysEnabled, setIgnoreRepaint, setLocale, setLocation, setName, setSize, setSize, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface javax.swing.plaf.basic.ComboPopup

      `isVisible`

- - ### Field Detail

    - #### comboBox

          protected JComboBox comboBox

    - #### list

          protected JList list

      This protected field is implementation specific. Do not access directly or override. Use the accessor methods instead.
      See Also:
        `getList()`, `createList()`

    - #### scroller

          protected JScrollPane scroller

      This protected field is implementation specific. Do not access directly or override. Use the create method instead
      See Also:
        `createScroller()`

    - #### valueIsAdjusting

          protected boolean valueIsAdjusting

      As of Java 2 platform v1.4 this previously undocumented field is no longer used.

    - #### mouseMotionListener

          protected MouseMotionListener mouseMotionListener

      This protected field is implementation specific. Do not access directly or override. Use the accessor or create methods instead.
      See Also:
        `getMouseMotionListener()`, `createMouseMotionListener()`

    - #### mouseListener

          protected MouseListener mouseListener

      This protected field is implementation specific. Do not access directly or override. Use the accessor or create methods instead.
      See Also:
        `getMouseListener()`, `createMouseListener()`

    - #### keyListener

          protected KeyListener keyListener

      This protected field is implementation specific. Do not access directly or override. Use the accessor or create methods instead.
      See Also:
        `getKeyListener()`, `createKeyListener()`

    - #### listSelectionListener

          protected ListSelectionListener listSelectionListener

      This protected field is implementation specific. Do not access directly or override. Use the create method instead.
      See Also:
        `createListSelectionListener()`

    - #### listMouseListener

          protected MouseListener listMouseListener

      This protected field is implementation specific. Do not access directly or override. Use the create method instead.
      See Also:
        `createListMouseListener()`

    - #### listMouseMotionListener

          protected MouseMotionListener listMouseMotionListener

      This protected field is implementation specific. Do not access directly or override. Use the create method instead
      See Also:
        `createListMouseMotionListener()`

    - #### propertyChangeListener

          protected PropertyChangeListener propertyChangeListener

      This protected field is implementation specific. Do not access directly or override. Use the create method instead
      See Also:
        `createPropertyChangeListener()`

    - #### listDataListener

          protected ListDataListener listDataListener

      This protected field is implementation specific. Do not access directly or override. Use the create method instead
      See Also:
        `createListDataListener()`

    - #### itemListener

          protected ItemListener itemListener

      This protected field is implementation specific. Do not access directly or override. Use the create method instead
      See Also:
        `createItemListener()`

    - #### autoscrollTimer

          protected Timer autoscrollTimer

      This protected field is implementation specific. Do not access directly or override.

    - #### hasEntered

          protected boolean hasEntered

    - #### isAutoScrolling

          protected boolean isAutoScrolling

    - #### scrollDirection

          protected int scrollDirection

    - #### SCROLL_UP

          protected static final int SCROLL_UP

      See Also:
        Constant Field Values

    - #### SCROLL_DOWN

          protected static final int SCROLL_DOWN

      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### BasicComboPopup

          public BasicComboPopup(JComboBox combo)

  - ### Method Detail

    - #### show

          public void show()

      Implementation of ComboPopup.show().
      Specified by:
        `show` in interface `ComboPopup`
      Overrides:
        `show` in class `Component`

    - #### hide

          public void hide()

      Implementation of ComboPopup.hide().
      Specified by:
        `hide` in interface `ComboPopup`
      Overrides:
        `hide` in class `JComponent`

    - #### getList

          public JList getList()

      Implementation of ComboPopup.getList().
      Specified by:
        `getList` in interface `ComboPopup`

    - #### getMouseListener

          public MouseListener getMouseListener()

      Implementation of ComboPopup.getMouseListener().
      Specified by:
        `getMouseListener` in interface `ComboPopup`
      Returns:
        a `MouseListener` or null
      See Also:
        `ComboPopup.getMouseListener()`

    - #### getMouseMotionListener

          public MouseMotionListener getMouseMotionListener()

      Implementation of ComboPopup.getMouseMotionListener().
      Specified by:
        `getMouseMotionListener` in interface `ComboPopup`
      Returns:
        a `MouseMotionListener` or null
      See Also:
        `ComboPopup.getMouseMotionListener()`

    - #### getKeyListener

          public KeyListener getKeyListener()

      Implementation of ComboPopup.getKeyListener().
      Specified by:
        `getKeyListener` in interface `ComboPopup`
      Returns:
        a `KeyListener` or null
      See Also:
        `ComboPopup.getKeyListener()`

    - #### uninstallingUI

          public void uninstallingUI()

      Called when the UI is uninstalling. Since this popup isn't in the component tree, it won't get it's uninstallUI() called. It removes the listeners that were added in addComboBoxListeners().
      Specified by:
        `uninstallingUI` in interface `ComboPopup`

    - #### uninstallComboBoxModelListeners

          protected void uninstallComboBoxModelListeners(ComboBoxModel model)

      Removes the listeners from the combo box model
      Parameters:
        `model` - The combo box model to install listeners
      See Also:
        `installComboBoxModelListeners(javax.swing.ComboBoxModel)`

    - #### uninstallKeyboardActions

          protected void uninstallKeyboardActions()

    - #### firePopupMenuWillBecomeVisible

          protected void firePopupMenuWillBecomeVisible()

      Description copied from class: `JPopupMenu`
      Notifies `PopupMenuListener`s that this popup menu will become visible.
      Overrides:
        `firePopupMenuWillBecomeVisible` in class `JPopupMenu`

    - #### firePopupMenuWillBecomeInvisible

          protected void firePopupMenuWillBecomeInvisible()

      Description copied from class: `JPopupMenu`
      Notifies `PopupMenuListener`s that this popup menu will become invisible.
      Overrides:
        `firePopupMenuWillBecomeInvisible` in class `JPopupMenu`

    - #### firePopupMenuCanceled

          protected void firePopupMenuCanceled()

      Description copied from class: `JPopupMenu`
      Notifies `PopupMenuListeners` that this popup menu is cancelled.
      Overrides:
        `firePopupMenuCanceled` in class `JPopupMenu`

    - #### createMouseListener

          protected MouseListener createMouseListener()

      Creates a listener that will watch for mouse-press and release events on the combo box. Warning: When overriding this method, make sure to maintain the existing behavior.
      Returns:
        a `MouseListener` which will be added to the combo box or null

    - #### createMouseMotionListener

          protected MouseMotionListener createMouseMotionListener()

      Creates the mouse motion listener which will be added to the combo box. Warning: When overriding this method, make sure to maintain the existing behavior.
      Returns:
        a `MouseMotionListener` which will be added to the combo box or null

    - #### createKeyListener

          protected KeyListener createKeyListener()

      Creates the key listener that will be added to the combo box. If this method returns null then it will not be added to the combo box.
      Returns:
        a `KeyListener` or null

    - #### createListSelectionListener

          protected ListSelectionListener createListSelectionListener()

      Creates a list selection listener that watches for selection changes in the popup's list. If this method returns null then it will not be added to the popup list.
      Returns:
        an instance of a `ListSelectionListener` or null

    - #### createListDataListener

          protected ListDataListener createListDataListener()

      Creates a list data listener which will be added to the `ComboBoxModel`. If this method returns null then it will not be added to the combo box model.
      Returns:
        an instance of a `ListDataListener` or null

    - #### createListMouseListener

          protected MouseListener createListMouseListener()

      Creates a mouse listener that watches for mouse events in the popup's list. If this method returns null then it will not be added to the combo box.
      Returns:
        an instance of a `MouseListener` or null

    - #### createListMouseMotionListener

          protected MouseMotionListener createListMouseMotionListener()

      Creates a mouse motion listener that watches for mouse motion events in the popup's list. If this method returns null then it will not be added to the combo box.
      Returns:
        an instance of a `MouseMotionListener` or null

    - #### createPropertyChangeListener

          protected PropertyChangeListener createPropertyChangeListener()

      Creates a `PropertyChangeListener` which will be added to the combo box. If this method returns null then it will not be added to the combo box.
      Returns:
        an instance of a `PropertyChangeListener` or null

    - #### createItemListener

          protected ItemListener createItemListener()

      Creates an `ItemListener` which will be added to the combo box. If this method returns null then it will not be added to the combo box.

      Subclasses may override this method to return instances of their own ItemEvent handlers.

      Returns:
        an instance of an `ItemListener` or null

    - #### createList

          protected JList createList()

      Creates the JList used in the popup to display the items in the combo box model. This method is called when the UI class is created.
      Returns:
        a `JList` used to display the combo box items

    - #### configureList

          protected void configureList()

      Configures the list which is used to hold the combo box items in the popup. This method is called when the UI class is created.
      See Also:
        `createList()`

    - #### installListListeners

          protected void installListListeners()

      Adds the listeners to the list control.

    - #### createScroller

          protected JScrollPane createScroller()

      Creates the scroll pane which houses the scrollable list.

    - #### configureScroller

          protected void configureScroller()

      Configures the scrollable portion which holds the list within the combo box popup. This method is called when the UI class is created.

    - #### configurePopup

          protected void configurePopup()

      Configures the popup portion of the combo box. This method is called when the UI class is created.

    - #### installComboBoxListeners

          protected void installComboBoxListeners()

      This method adds the necessary listeners to the JComboBox.

    - #### installComboBoxModelListeners

          protected void installComboBoxModelListeners(ComboBoxModel model)

      Installs the listeners on the combo box model. Any listeners installed on the combo box model should be removed in `uninstallComboBoxModelListeners`.
      Parameters:
        `model` - The combo box model to install listeners
      See Also:
        `uninstallComboBoxModelListeners(javax.swing.ComboBoxModel)`

    - #### installKeyboardActions

          protected void installKeyboardActions()

    - #### isFocusTraversable

          public boolean isFocusTraversable()

      Overridden to unconditionally return false.
      Overrides:
        `isFocusTraversable` in class `Component`
      Returns:
        `true` if this `Component` is focusable; `false` otherwise
      See Also:
        `Component.setFocusable(boolean)`

    - #### startAutoScrolling

          protected void startAutoScrolling(int direction)

      This protected method is implementation specific and should be private. do not call or override.

    - #### stopAutoScrolling

          protected void stopAutoScrolling()

      This protected method is implementation specific and should be private. do not call or override.

    - #### autoScrollUp

          protected void autoScrollUp()

      This protected method is implementation specific and should be private. do not call or override.

    - #### autoScrollDown

          protected void autoScrollDown()

      This protected method is implementation specific and should be private. do not call or override.

    - #### getAccessibleContext

          public AccessibleContext getAccessibleContext()

      Gets the AccessibleContext associated with this BasicComboPopup. The AccessibleContext will have its parent set to the ComboBox.
      Specified by:
        `getAccessibleContext` in interface `Accessible`
      Overrides:
        `getAccessibleContext` in class `JPopupMenu`
      Returns:
        an AccessibleContext for the BasicComboPopup
      Since:
        1.5

    - #### delegateFocus

          protected void delegateFocus(MouseEvent e)

      This is is a utility method that helps event handlers figure out where to send the focus when the popup is brought up. The standard implementation delegates the focus to the editor (if the combo box is editable) or to the JComboBox if it is not editable.

    - #### togglePopup

          protected void togglePopup()

      Makes the popup visible if it is hidden and makes it hidden if it is visible.

    - #### convertMouseEvent

          protected MouseEvent convertMouseEvent(MouseEvent e)

    - #### getPopupHeightForRowCount

          protected int getPopupHeightForRowCount(int maxRowCount)

      Retrieves the height of the popup based on the current ListCellRenderer and the maximum row count.

    - #### computePopupBounds

          protected Rectangle computePopupBounds(int px,
                                     int py,
                                     int pw,
                                     int ph)

      Calculate the placement and size of the popup portion of the combo box based on the combo box location and the enclosing screen bounds. If no transformations are required, then the returned rectangle will have the same values as the parameters.
      Parameters:
        `px` - starting x location
        `py` - starting y location
        `pw` - starting width
        `ph` - starting height
      Returns:
        a rectangle which represents the placement and size of the popup

    - #### updateListBoxSelectionForEvent

          protected void updateListBoxSelectionForEvent(MouseEvent anEvent,
                                            boolean shouldScroll)

      A utility method used by the event listeners. Given a mouse event, it changes the list selection to the list item below the mouse.

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