public class FixedJComboBox<E> extends JComboBox<E>
The problem is to do with firing ActionEvents when the
ComboBoxModel is changed.
According to the JComboBox.addActionListener(java.awt.event.ActionListener)
documentation, ActionListeners should only be informed when a
selection is made, that is when the selection changes.
In general that's true, an ActionEvent is only fired when the
model selection changes, but at least in Oracle Java 8/OpenJDK 8
such an event can be fired if the model content (list data) changes
but the current selection is null both before and after that change
(if the selection is an particular non-null value before and after,
no ActionEvent is fired, as expected).
Since there are a lot of listeners on these selectors in topcat,
and certain user actions can cause a large number of changes to
the model without changing the selection, this can cause a lot of
unnecessary events to be fired, which can in some circumstances
result in genuine responsiveness issues.
This class overrides the contentsChanged(javax.swing.event.ListDataEvent) method,
and enough other methods to make that work, so that no event is fired
in the event of a null->null selection change.
JComboBox.AccessibleJComboBox, JComboBox.KeySelectionManagerJComponent.AccessibleJComponentContainer.AccessibleAWTContainerComponent.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategyactionCommand, dataModel, editor, isEditable, keySelectionManager, lightWeightPopupEnabled, maximumRowCount, renderer, selectedItemReminderlistenerList, TOOL_TIP_TEXT_KEY, ui, UNDEFINED_CONDITION, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, WHEN_FOCUSED, WHEN_IN_FOCUSED_WINDOWaccessibleContext, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENTABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH| Constructor and Description |
|---|
FixedJComboBox()
Creates a JComboBox with a default data model.
|
FixedJComboBox(ComboBoxModel<E> model)
Creates a JComboBox that takes its items from an existing ComboBoxModel.
|
FixedJComboBox(E[] items)
Creates a JComboBox that contains the elements in the specified array.
|
| Modifier and Type | Method and Description |
|---|---|
void |
contentsChanged(ListDataEvent evt)
Overriding this method is questionable, since the OpenJDK javadoc says:
"This method is public as an implementation side effect.
|
void |
removeAllItems() |
protected void |
selectedItemChanged() |
void |
setModel(ComboBoxModel<E> model) |
actionPerformed, actionPropertyChanged, addActionListener, addItem, addItemListener, addPopupMenuListener, configureEditor, configurePropertiesFromAction, createActionPropertyChangeListener, createDefaultKeySelectionManager, fireActionEvent, fireItemStateChanged, firePopupMenuCanceled, firePopupMenuWillBecomeInvisible, firePopupMenuWillBecomeVisible, getAccessibleContext, getAction, getActionCommand, getActionListeners, getEditor, getItemAt, getItemCount, getItemListeners, getKeySelectionManager, getMaximumRowCount, getModel, getPopupMenuListeners, getPrototypeDisplayValue, getRenderer, getSelectedIndex, getSelectedItem, getSelectedObjects, getUI, getUIClassID, hidePopup, insertItemAt, installAncestorListener, intervalAdded, intervalRemoved, isEditable, isLightWeightPopupEnabled, isPopupVisible, paramString, processKeyBinding, processKeyEvent, removeActionListener, removeItem, removeItemAt, removeItemListener, removePopupMenuListener, selectWithKeyChar, setAction, setActionCommand, setEditable, setEditor, setEnabled, setKeySelectionManager, setLightWeightPopupEnabled, setMaximumRowCount, setPopupVisible, setPrototypeDisplayValue, setRenderer, setSelectedIndex, setSelectedItem, setUI, showPopup, updateUIaddAncestorListener, 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, hide, isDoubleBuffered, isLightweightComponent, isManagingFocus, isOpaque, isOptimizedDrawingEnabled, isPaintingForPrint, isPaintingOrigin, isPaintingTile, isRequestFocusEnabled, isValidateRoot, paint, paintBorder, paintChildren, paintComponent, paintImmediately, paintImmediately, print, printAll, printBorder, printChildren, printComponent, processComponentKeyEvent, 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, setFocusTraversalKeys, setFont, setForeground, setInheritsPopupMenu, setInputMap, setInputVerifier, setMaximumSize, setMinimumSize, setNextFocusableComponent, setOpaque, setPreferredSize, setRequestFocusEnabled, setToolTipText, setTransferHandler, setUI, setVerifyInputWhenFocusTarget, setVisible, unregisterKeyboardAction, updateadd, 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, remove, removeAll, removeContainerListener, setComponentZOrder, setFocusCycleRoot, setFocusTraversalPolicy, setFocusTraversalPolicyProvider, setLayout, transferFocusDownCycle, validate, validateTreeaction, 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, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, processComponentEvent, processFocusEvent, 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, setLocation, setName, setSize, setSize, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCyclepublic FixedJComboBox()
public FixedJComboBox(ComboBoxModel<E> model)
model - modelpublic FixedJComboBox(E[] items)
items - array populating default combo box modelpublic void contentsChanged(ListDataEvent evt)
However if an attempt is made to compile this class against a JDK
in which JComboBox lacks the contentsChanged method,
there will be trouble.
It could be averted by removing the @Override annotation,
and invoking the superclass method using reflection.
contentsChanged in interface ListDataListenercontentsChanged in class JComboBox<E>public void setModel(ComboBoxModel<E> model)
public void removeAllItems()
removeAllItems in class JComboBox<E>protected void selectedItemChanged()
selectedItemChanged in class JComboBox<E>Copyright © 2003-2025 CCLRC: Council for the Central Laboratory of the Research Councils. All Rights Reserved.