Module java.desktop
Package javax.swing.plaf.basic

# Class BasicComboBoxUI

java.lang.Object
javax.swing.plaf.ComponentUI
javax.swing.plaf.ComboBoxUI
javax.swing.plaf.basic.BasicComboBoxUI

Direct Known Subclasses:
  `MetalComboBoxUI`, `SynthComboBoxUI`

public class BasicComboBoxUI extends ComboBoxUI
Basic UI implementation for JComboBox.

The combo box is a compound component which means that it is an aggregate of many simpler components. This class creates and manages the listeners on the combo box and the combo box model. These listeners update the user interface in response to changes in the properties and state 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.

For adding specific actions, override `installKeyboardActions` to add actions in response to KeyStroke bindings. See the article How to Use Key Bindings

## Nested Class Summary

Nested Classes
Modifier and Type
Class
Description
`class`
`BasicComboBoxUI.ComboBoxLayoutManager`
This layout manager handles the 'standard' layout of combo boxes.
`class`
`BasicComboBoxUI.FocusHandler`
This listener hides the popup when the focus is lost.
`class`
`BasicComboBoxUI.ItemHandler`
This listener watches for changes to the selection in the combo box.
`class`
`BasicComboBoxUI.KeyHandler`
This listener checks to see if the key event isn't a navigation key.
`class`
`BasicComboBoxUI.ListDataHandler`
This listener watches for changes in the `ComboBoxModel`.
`class`
`BasicComboBoxUI.PropertyChangeHandler`
This listener watches for bound properties that have changed in the combo box.

## Field Summary

Fields
Modifier and Type
Field
Description
`protected JButton`
`arrowButton`
The arrow button that invokes the popup.
`protected Dimension`
`cachedMinimumSize`
The cached minimum preferred size.
`protected JComboBox<Object>`
`comboBox`
The instance of `JComboBox`.
`protected CellRendererPane`
`currentValuePane`
Used to render the currently selected item in the combo box.
`protected Component`
`editor`
The Component that the `ComboBoxEditor` uses for editing.
`protected FocusListener`
`focusListener`
This protected field is implementation specific.
`protected boolean`
`hasFocus`
This protected field is implementation specific.
`protected boolean`
`isMinimumSizeDirty`
The flag for recalculating the minimum preferred size.
`protected ItemListener`
`itemListener`
This protected field is implementation specific.
`protected KeyListener`
`keyListener`
This protected field is implementation specific.
`protected JList<Object>`
`listBox`
This list is for drawing the current item in the combo box.
`protected ListDataListener`
`listDataListener`
This protected field is implementation specific.
`protected Insets`
`padding`
If specified, these insets act as padding around the cell renderer when laying out and painting the "selected" item in the combo box.
`protected ComboPopup`
`popup`
The implementation of `ComboPopup` that is used to show the popup.
`protected KeyListener`
`popupKeyListener`
The `KeyListener` listens to events.
`protected MouseListener`
`popupMouseListener`
The `MouseListener` listens to events.
`protected MouseMotionListener`
`popupMouseMotionListener`
The `MouseMotionListener` listens to events.
`protected PropertyChangeListener`
`propertyChangeListener`
This protected field is implementation specific.
`protected boolean`
`squareButton`
Indicates whether or not the combo box button should be square.

## Constructor Summary

Constructors
Constructor
Description
`BasicComboBoxUI()`
Constructs a `BasicComboBoxUI`.

## Method Summary

Modifier and Type
Method
Description
`void`
`addEditor()`
This public method is implementation specific and should be private.
`void`
`configureArrowButton()`
This public method is implementation specific and should be private.
`protected void`
`configureEditor()`
This protected method is implementation specific and should be private.
`protected JButton`
`createArrowButton()`
Creates a button which will be used as the control to show or hide the popup portion of the combo box.
`protected ComboBoxEditor`
`createEditor()`
Creates the default editor that will be used in editable combo boxes.
`protected FocusListener`
`createFocusListener()`
Creates a `FocusListener` which will be added to the combo box.
`protected ItemListener`
`createItemListener()`
Creates an `ItemListener` which will be added to the combo box.
`protected KeyListener`
`createKeyListener()`
Creates a `KeyListener` which will be added to the combo box.
`protected LayoutManager`
`createLayoutManager()`
Creates a layout manager for managing the components which make up the combo box.
`protected ListDataListener`
`createListDataListener()`
Creates a list data listener which will be added to the `ComboBoxModel`.
`protected ComboPopup`
`createPopup()`
Creates the popup portion of the combo box.
`protected PropertyChangeListener`
`createPropertyChangeListener()`
Creates a `PropertyChangeListener` which will be added to the combo box.
`protected ListCellRenderer<Object>`
`createRenderer()`
Creates the default renderer that will be used in a non-editiable combo box.
`static ComponentUI`
`createUI(JComponent c)`
Constructs a new instance of `BasicComboBoxUI`.
`int`
`getBaseline(JComponent c, int width, int height)`
Returns the baseline.
`Component.BaselineResizeBehavior`
`getBaselineResizeBehavior(JComponent c)`
Returns an enum indicating how the baseline of the component changes as the size changes.
`protected Dimension`
`getDefaultSize()`
Return the default size of an empty display area of the combo box using the current renderer and font.
`protected Dimension`
`getDisplaySize()`
Returns the calculated size of the display area.
`protected Insets`
`getInsets()`
Gets the insets from the JComboBox.
`Dimension`
`getMinimumSize(JComponent c)`
The minimum size is the size of the display area plus insets plus the button.
`protected Dimension`
`getSizeForComponent(Component comp)`
Returns the size a component would have if used as a cell renderer.
`protected void`
`installComponents()`
Creates and initializes the components which make up the aggregate combo box.
`protected void`
`installDefaults()`
Installs the default colors, default font, default renderer, and default editor into the JComboBox.
`protected void`
`installKeyboardActions()`
Adds keyboard actions to the JComboBox.
`protected void`
`installListeners()`
Creates and installs listeners for the combo box and its model.
`boolean`
`isFocusTraversable(JComboBox<?> c)`
Determines if the JComboBox is focus traversable.
`protected boolean`
`isNavigationKey(int keyCode)`
Returns whether or not the supplied keyCode maps to a key that is used for navigation.
`boolean`
`isPopupVisible(JComboBox<?> c)`
Tells if the popup is visible or not.
`void`
`paintCurrentValue(Graphics g, Rectangle bounds, boolean hasFocus)`
Paints the currently selected item.
`void`
`paintCurrentValueBackground(Graphics g, Rectangle bounds, boolean hasFocus)`
Paints the background of the currently selected item.
`protected Rectangle`
`rectangleForCurrentValue()`
Returns the area that is reserved for drawing the currently selected item.
`void`
`removeEditor()`
This public method is implementation specific and should be private.
`protected void`
`selectNextPossibleValue()`
Selects the next item in the list.
`protected void`
`selectPreviousPossibleValue()`
Selects the previous item in the list.
`void`
`setPopupVisible(JComboBox<?> c, boolean v)`
Hides the popup.
`protected void`
`toggleOpenClose()`
Hides the popup if it is showing and shows the popup if it is hidden.
`void`
`unconfigureArrowButton()`
This public method is implementation specific and should be private.
`protected void`
`unconfigureEditor()`
This protected method is implementation specific and should be private.
`protected void`
`uninstallComponents()`
The aggregate components which comprise the combo box are unregistered and uninitialized.
`protected void`
`uninstallDefaults()`
Uninstalls the default colors, default font, default renderer, and default editor from the combo box.
`protected void`
`uninstallKeyboardActions()`
Removes the focus InputMap and ActionMap.
`protected void`
`uninstallListeners()`
Removes the installed listeners from the combo box and its model.

### Methods declared in class javax.swing.plaf.ComponentUI

`contains, getAccessibleChild, getAccessibleChildrenCount, getMaximumSize, getPreferredSize, installUI, paint, uninstallUI, update`

### Methods declared in class java.lang.Object

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

## Field Details

### comboBox

protected JComboBox<Object> comboBox
The instance of `JComboBox`.

### hasFocus

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

### listBox

protected JList<Object> listBox
This list is for drawing the current item in the combo box.

### currentValuePane

protected CellRendererPane currentValuePane
Used to render the currently selected item in the combo box. It doesn't have anything to do with the popup's rendering.

### popup

protected ComboPopup popup
The implementation of `ComboPopup` that is used to show the popup.

### editor

protected Component editor
The Component that the `ComboBoxEditor` uses for editing.

### arrowButton

protected JButton arrowButton
The arrow button that invokes the popup.

### keyListener

protected KeyListener keyListener
This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
  - `createKeyListener()`

### focusListener

protected FocusListener focusListener
This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
  - `createFocusListener()`

### propertyChangeListener

protected PropertyChangeListener propertyChangeListener
This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
  - `createPropertyChangeListener()`

### itemListener

protected ItemListener itemListener
This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
  - `createItemListener()`

### popupMouseListener

protected MouseListener popupMouseListener
The `MouseListener` listens to events.

### popupMouseMotionListener

protected MouseMotionListener popupMouseMotionListener
The `MouseMotionListener` listens to events.

### popupKeyListener

protected KeyListener popupKeyListener
The `KeyListener` listens to events.

### listDataListener

protected ListDataListener listDataListener
This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
  - `createListDataListener()`

### isMinimumSizeDirty

protected boolean isMinimumSizeDirty
The flag for recalculating the minimum preferred size.

### cachedMinimumSize

protected Dimension cachedMinimumSize
The cached minimum preferred size.

### squareButton

protected boolean squareButton
Indicates whether or not the combo box button should be square. If square, then the width and height are equal, and are both set to the height of the combo minus appropriate insets.

Since:
  1.7

### padding

protected Insets padding
If specified, these insets act as padding around the cell renderer when laying out and painting the "selected" item in the combo box. These insets add to those specified by the cell renderer.

Since:
  1.7

## Constructor Details

### BasicComboBoxUI

public BasicComboBoxUI()
Constructs a `BasicComboBoxUI`.

## Method Details

### createUI

public static ComponentUI createUI(JComponent c)
Constructs a new instance of `BasicComboBoxUI`.

Parameters:
  `c` - a component
Returns:
  a new instance of `BasicComboBoxUI`

### installDefaults

protected void installDefaults()
Installs the default colors, default font, default renderer, and default editor into the JComboBox.

### installListeners

protected void installListeners()
Creates and installs listeners for the combo box and its model. This method is called when the UI is installed.

### uninstallDefaults

protected void uninstallDefaults()
Uninstalls the default colors, default font, default renderer, and default editor from the combo box.

### uninstallListeners

protected void uninstallListeners()
Removes the installed listeners from the combo box and its model. The number and types of listeners removed and in this method should be the same that was added in `installListeners`

### createPopup

protected ComboPopup createPopup()
Creates the popup portion of the combo box.

Returns:
  an instance of `ComboPopup`
See Also:
  - `ComboPopup`

### createKeyListener

protected KeyListener createKeyListener()
Creates a `KeyListener` 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 `KeyListener` or null

### createFocusListener

protected FocusListener createFocusListener()
Creates a `FocusListener` 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 `FocusListener` 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

### 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

### 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

### createLayoutManager

protected LayoutManager createLayoutManager()
Creates a layout manager for managing the components which make up the combo box.

Returns:
  an instance of a layout manager

### createRenderer

protected ListCellRenderer<Object> createRenderer()
Creates the default renderer that will be used in a non-editiable combo box. A default renderer will used only if a renderer has not been explicitly set with `setRenderer`.

Returns:
  a `ListCellRender` used for the combo box
See Also:
  - `JComboBox.setRenderer(javax.swing.ListCellRenderer<? super E>)`

### createEditor

protected ComboBoxEditor createEditor()
Creates the default editor that will be used in editable combo boxes. A default editor will be used only if an editor has not been explicitly set with `setEditor`.

Returns:
  a `ComboBoxEditor` used for the combo box
See Also:
  - `JComboBox.setEditor(javax.swing.ComboBoxEditor)`

### installComponents

protected void installComponents()
Creates and initializes the components which make up the aggregate combo box. This method is called as part of the UI installation process.

### uninstallComponents

protected void uninstallComponents()
The aggregate components which comprise the combo box are unregistered and uninitialized. This method is called as part of the UI uninstallation process.

### addEditor

public void addEditor()
This public method is implementation specific and should be private. do not call or override. To implement a specific editor create a custom `ComboBoxEditor`

See Also:
  - `createEditor()`
  - `JComboBox.setEditor(javax.swing.ComboBoxEditor)`
  - `ComboBoxEditor`

### removeEditor

public void removeEditor()
This public method is implementation specific and should be private. do not call or override.

See Also:
  - `addEditor()`

### configureEditor

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

See Also:
  - `addEditor()`

### unconfigureEditor

protected void unconfigureEditor()
This protected method is implementation specific and should be private. Do not call or override.

See Also:
  - `addEditor()`

### configureArrowButton

public void configureArrowButton()
This public method is implementation specific and should be private. Do not call or override.

See Also:
  - `createArrowButton()`

### unconfigureArrowButton

public void unconfigureArrowButton()
This public method is implementation specific and should be private. Do not call or override.

See Also:
  - `createArrowButton()`

### createArrowButton

protected JButton createArrowButton()
Creates a button which will be used as the control to show or hide the popup portion of the combo box.

Returns:
  a button which represents the popup control

### isPopupVisible

public boolean isPopupVisible(JComboBox<?> c)
Tells if the popup is visible or not.

Specified by:
  `isPopupVisible` in class `ComboBoxUI`
Parameters:
  `c` - a `JComboBox`
Returns:
  true if popup of the `JComboBox` is visible

### setPopupVisible

public void setPopupVisible(JComboBox<?> c, boolean v)
Hides the popup.

Specified by:
  `setPopupVisible` in class `ComboBoxUI`
Parameters:
  `c` - a `JComboBox`
  `v` - a `boolean` determining the visibility of the popup

### isFocusTraversable

public boolean isFocusTraversable(JComboBox<?> c)
Determines if the JComboBox is focus traversable. If the JComboBox is editable this returns false, otherwise it returns true.

Specified by:
  `isFocusTraversable` in class `ComboBoxUI`
Parameters:
  `c` - a `JComboBox`
Returns:
  true if the given `JComboBox` is traversable

### getMinimumSize

public Dimension getMinimumSize(JComponent c)
The minimum size is the size of the display area plus insets plus the button.

Overrides:
  `getMinimumSize` in class `ComponentUI`
Parameters:
  `c` - the component whose minimum size is being queried; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
Returns:
  a `Dimension` object or `null`
See Also:
  - `JComponent.getMinimumSize()`
  - `LayoutManager.minimumLayoutSize(java.awt.Container)`
  - `ComponentUI.getPreferredSize(javax.swing.JComponent)`

### getBaseline

public int getBaseline(JComponent c, int width, int height)
Returns the baseline.

Overrides:
  `getBaseline` in class `ComponentUI`
Parameters:
  `c` - `JComponent` baseline is being requested for
  `width` - the width to get the baseline for
  `height` - the height to get the baseline for
Returns:
  baseline or a value < 0 indicating there is no reasonable baseline
Throws:
  `NullPointerException` - if `c` is `null`
  `IllegalArgumentException` - if width or height is < 0
Since:
  1.6
See Also:
  - `JComponent.getBaseline(int, int)`

### getBaselineResizeBehavior

public Component.BaselineResizeBehavior getBaselineResizeBehavior(JComponent c)
Returns an enum indicating how the baseline of the component changes as the size changes.

Overrides:
  `getBaselineResizeBehavior` in class `ComponentUI`
Parameters:
  `c` - `JComponent` to return baseline resize behavior for
Returns:
  an enum indicating how the baseline changes as the component size changes
Throws:
  `NullPointerException` - if `c` is `null`
Since:
  1.6
See Also:
  - `JComponent.getBaseline(int, int)`

### isNavigationKey

protected boolean isNavigationKey(int keyCode)
Returns whether or not the supplied keyCode maps to a key that is used for navigation. This is used for optimizing key input by only passing non- navigation keys to the type-ahead mechanism. Subclasses should override this if they change the navigation keys.

Parameters:
  `keyCode` - a key code
Returns:
  `true` if the supplied `keyCode` maps to a navigation key

### selectNextPossibleValue

protected void selectNextPossibleValue()
Selects the next item in the list. It won't change the selection if the currently selected item is already the last item.

### selectPreviousPossibleValue

protected void selectPreviousPossibleValue()
Selects the previous item in the list. It won't change the selection if the currently selected item is already the first item.

### toggleOpenClose

protected void toggleOpenClose()
Hides the popup if it is showing and shows the popup if it is hidden.

### rectangleForCurrentValue

protected Rectangle rectangleForCurrentValue()
Returns the area that is reserved for drawing the currently selected item.

Returns:
  the area that is reserved for drawing the currently selected item

### getInsets

protected Insets getInsets()
Gets the insets from the JComboBox.

Returns:
  the insets

### paintCurrentValue

public void paintCurrentValue(Graphics g, Rectangle bounds, boolean hasFocus)
Paints the currently selected item.

Parameters:
  `g` - an instance of `Graphics`
  `bounds` - a bounding rectangle to render to
  `hasFocus` - is focused

### paintCurrentValueBackground

public void paintCurrentValueBackground(Graphics g, Rectangle bounds, boolean hasFocus)
Paints the background of the currently selected item.

Parameters:
  `g` - an instance of `Graphics`
  `bounds` - a bounding rectangle to render to
  `hasFocus` - is focused

### getDefaultSize

protected Dimension getDefaultSize()
Return the default size of an empty display area of the combo box using the current renderer and font.

Returns:
  the size of an empty display area
See Also:
  - `getDisplaySize()`

### getDisplaySize

protected Dimension getDisplaySize()
Returns the calculated size of the display area. The display area is the portion of the combo box in which the selected item is displayed. This method will use the prototype display value if it has been set.

For combo boxes with a non trivial number of items, it is recommended to use a prototype display value to significantly speed up the display size calculation.

Returns:
  the size of the display area calculated from the combo box items
See Also:
  - `JComboBox.setPrototypeDisplayValue(E)`

### getSizeForComponent

protected Dimension getSizeForComponent(Component comp)
Returns the size a component would have if used as a cell renderer.

Parameters:
  `comp` - a `Component` to check
Returns:
  size of the component
Since:
  1.7

### installKeyboardActions

protected void installKeyboardActions()
Adds keyboard actions to the JComboBox. Actions on enter and esc are already supplied. Add more actions as you need them.

### uninstallKeyboardActions

protected void uninstallKeyboardActions()
Removes the focus InputMap and ActionMap.