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Java javax.swing.text Class DefaultCaret（JDK8）

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Java™ Platform
Standard Ed. 8
javax.swing.text

Class DefaultCaret

  • All Implemented Interfaces:
    FocusListener, MouseListener, MouseMotionListener, Shape, Serializable, Cloneable, EventListener, Caret
    Direct Known Subclasses:
    BasicTextUI.BasicCaret 

    public class DefaultCaret
extends Rectangle
implements Caret, FocusListener, MouseListener, MouseMotionListener
    A default implementation of Caret. The caret is rendered as a vertical line in the color specified by the CaretColor property of the associated JTextComponent. It can blink at the rate specified by the BlinkRate property.

    This implementation expects two sources of asynchronous notification. The timer thread fires asynchronously, and causes the caret to simply repaint the most recent bounding box. The caret also tracks change as the document is modified. Typically this will happen on the event dispatch thread as a result of some mouse or keyboard event. The caret behavior on both synchronous and asynchronous documents updates is controlled by UpdatePolicy property. The repaint of the new caret location will occur on the event thread in any case, as calls to modelToView are only safe on the event thread.

    The caret acts as a mouse and focus listener on the text component it has been installed in, and defines the caret semantics based upon those events. The listener methods can be reimplemented to change the semantics. By default, the first mouse button will be used to set focus and caret position. Dragging the mouse pointer with the first mouse button will sweep out a selection that is contiguous in the model. If the associated text component is editable, the caret will become visible when focus is gained, and invisible when focus is lost.

    The Highlighter bound to the associated text component is used to render the selection by default. Selection appearance can be customized by supplying a painter to use for the highlights. By default a painter is used that will render a solid color as specified in the associated text component in the SelectionColor property. This can easily be changed by reimplementing the getSelectionPainter method.

    A customized caret appearance can be achieved by reimplementing the paint method. If the paint method is changed, the damage method should also be reimplemented to cause a repaint for the area needed to render the caret. The caret extends the Rectangle class which is used to hold the bounding box for where the caret was last rendered. This enables the caret to repaint in a thread-safe manner when the caret moves without making a call to modelToView which is unstable between model updates and view repair (i.e. the order of delivery to DocumentListeners is not guaranteed).

    The magic caret position is set to null when the caret position changes. A timer is used to determine the new location (after the caret change). When the timer fires, if the magic caret position is still null it is reset to the current caret position. Any actions that change the caret position and want the magic caret position to remain the same, must remember the magic caret position, change the cursor, and then set the magic caret position to its original value. This has the benefit that only actions that want the magic caret position to persist (such as open/down) need to know about it.

    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 JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

    See Also:
    Caret

    • Field Detail

      • NEVER_UPDATE

        public static final int NEVER_UPDATE
        Indicates that the caret should remain at the same absolute position in the document regardless of any document updates, except when the document length becomes less than the current caret position due to removal. In that case the caret position is adjusted to the end of the document.
        Since:
        1.5
        See Also:
        setUpdatePolicy(int), getUpdatePolicy(), Constant Field Values

      • ALWAYS_UPDATE

        public static final int ALWAYS_UPDATE
        Indicates that the caret position is to be always updated accordingly to the document changes regardless whether the document updates are performed on the Event Dispatching Thread or not.
        Since:
        1.5
        See Also:
        setUpdatePolicy(int), getUpdatePolicy(), Constant Field Values

      • changeEvent

        protected transient ChangeEvent changeEvent
        The change event for the model. Only one ChangeEvent is needed per model instance since the event's only (read-only) state is the source property. The source of events generated here is always "this".

    • Constructor Detail

      • DefaultCaret

        public DefaultCaret()
        Constructs a default caret.

    • Method Detail

      • setUpdatePolicy

        public void setUpdatePolicy(int policy)
        Sets the caret movement policy on the document updates. Normally the caret updates its absolute position within the document on insertions occurred before or at the caret position and on removals before the caret position. 'Absolute position' means here the position relative to the start of the document. For example if a character is typed within editable text component it is inserted at the caret position and the caret moves to the next absolute position within the document due to insertion and if BACKSPACE is typed then caret decreases its absolute position due to removal of a character before it. Sometimes it may be useful to turn off the caret position updates so that the caret stays at the same absolute position within the document position regardless of any document updates.

        The following update policies are allowed:

        • NEVER_UPDATE: the caret stays at the same absolute position in the document regardless of any document updates, except when document length becomes less than the current caret position due to removal. In that case caret position is adjusted to the end of the document. The caret doesn't try to keep itself visible by scrolling the associated view when using this policy.
        • ALWAYS_UPDATE: the caret always tracks document changes. For regular changes it increases its position if an insertion occurs before or at its current position, and decreases position if a removal occurs before its current position. For undo/redo updates it is always moved to the position where update occurred. The caret also tries to keep itself visible by calling adjustVisibility method.
        • UPDATE_WHEN_ON_EDT: acts like ALWAYS_UPDATE if the document updates are performed on the Event Dispatching Thread and like NEVER_UPDATE if updates are performed on other thread.

        The default property value is UPDATE_WHEN_ON_EDT.

        Parameters:
        policy - one of the following values : UPDATE_WHEN_ON_EDT, NEVER_UPDATE, ALWAYS_UPDATE
        Throws:
        IllegalArgumentException - if invalid value is passed
        Since:
        1.5
        See Also:
        getUpdatePolicy(), adjustVisibility(java.awt.Rectangle), UPDATE_WHEN_ON_EDT, NEVER_UPDATE, ALWAYS_UPDATE

      • getComponent

        protected final JTextComponent getComponent()
        Gets the text editor component that this caret is is bound to.
        Returns:
        the component

      • repaint

        protected final void repaint()
        Cause the caret to be painted. The repaint area is the bounding box of the caret (i.e. the caret rectangle or this).

        This method is thread safe, although most Swing methods are not. Please see Concurrency in Swing for more information.

      • damage

        protected void damage(Rectangle r)
        Damages the area surrounding the caret to cause it to be repainted in a new location. If paint() is reimplemented, this method should also be reimplemented. This method should update the caret bounds (x, y, width, and height).
        Parameters:
        r - the current location of the caret
        See Also:
        paint(java.awt.Graphics)

      • adjustVisibility

        protected void adjustVisibility(Rectangle nloc)
        Scrolls the associated view (if necessary) to make the caret visible. Since how this should be done is somewhat of a policy, this method can be reimplemented to change the behavior. By default the scrollRectToVisible method is called on the associated component.
        Parameters:
        nloc - the new position to scroll to

      • getSelectionPainter

        protected Highlighter.HighlightPainter getSelectionPainter()
        Gets the painter for the Highlighter.
        Returns:
        the painter

      • positionCaret

        protected void positionCaret(MouseEvent e)
        Tries to set the position of the caret from the coordinates of a mouse event, using viewToModel().
        Parameters:
        e - the mouse event

      • moveCaret

        protected void moveCaret(MouseEvent e)
        Tries to move the position of the caret from the coordinates of a mouse event, using viewToModel(). This will cause a selection if the dot and mark are different.
        Parameters:
        e - the mouse event

      • mousePressed

        public void mousePressed(MouseEvent e)
        If button 1 is pressed, this is implemented to request focus on the associated text component, and to set the caret position. If the shift key is held down, the caret will be moved, potentially resulting in a selection, otherwise the caret position will be set to the new location. If the component is not enabled, there will be no request for focus.
        Specified by:
        mousePressed in interface MouseListener
        Parameters:
        e - the mouse event
        See Also:
        MouseListener.mousePressed(java.awt.event.MouseEvent)

      • paint

        public void paint(Graphics g)
        Renders the caret as a vertical line. If this is reimplemented the damage method should also be reimplemented as it assumes the shape of the caret is a vertical line. Sets the caret color to the value returned by getCaretColor().

        If there are multiple text directions present in the associated document, a flag indicating the caret bias will be rendered. This will occur only if the associated document is a subclass of AbstractDocument and there are multiple bidi levels present in the bidi element structure (i.e. the text has multiple directions associated with it).

        Specified by:
        paint in interface Caret
        Parameters:
        g - the graphics context
        See Also:
        damage(java.awt.Rectangle)

      • install

        public void install(JTextComponent c)
        Called when the UI is being installed into the interface of a JTextComponent. This can be used to gain access to the model that is being navigated by the implementation of this interface. Sets the dot and mark to 0, and establishes document, property change, focus, mouse, and mouse motion listeners.
        Specified by:
        install in interface Caret
        Parameters:
        c - the component
        See Also:
        Caret.install(javax.swing.text.JTextComponent)

      • fireStateChanged

        protected void fireStateChanged()
        Notifies all listeners that have registered interest for notification on this event type. The event instance is lazily created using the parameters passed into the fire method. The listener list is processed last to first.
        See Also:
        EventListenerList

      • getListeners

        public <T extends EventListener> T[] getListeners(Class<T> listenerType)
        Returns an array of all the objects currently registered as FooListeners upon this caret. FooListeners are registered using the addFooListener method.

        You can specify the listenerType argument with a class literal, such as FooListener.class. For example, you can query a DefaultCaret c for its change listeners with the following code:

        ChangeListener[] cls = (ChangeListener[])(c.getListeners(ChangeListener.class));
        If no such listeners exist, this method returns an empty array.
        Parameters:
        listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener
        Returns:
        an array of all objects registered as FooListeners on this component, or an empty array if no such listeners have been added
        Throws:
        ClassCastException - if listenerType doesn't specify a class or interface that implements java.util.EventListener
        Since:
        1.3
        See Also:
        getChangeListeners()

      • setSelectionVisible

        public void setSelectionVisible(boolean vis)
        Changes the selection visibility.
        Specified by:
        setSelectionVisible in interface Caret
        Parameters:
        vis - the new visibility

      • isSelectionVisible

        public boolean isSelectionVisible()
        Checks whether the current selection is visible.
        Specified by:
        isSelectionVisible in interface Caret
        Returns:
        true if the selection is visible

      • isActive

        public boolean isActive()
        Determines if the caret is currently active.

        This method returns whether or not the Caret is currently in a blinking state. It does not provide information as to whether it is currently blinked on or off. To determine if the caret is currently painted use the isVisible method.

        Returns:
        true if active else false
        Since:
        1.5
        See Also:
        isVisible()

      • isVisible

        public boolean isVisible()
        Indicates whether or not the caret is currently visible. As the caret flashes on and off the return value of this will change between true, when the caret is painted, and false, when the caret is not painted. isActive indicates whether or not the caret is in a blinking state, such that it can be visible, and isVisible indicates whether or not the caret is actually visible.

        Subclasses that wish to render a different flashing caret should override paint and only paint the caret if this method returns true.

        Specified by:
        isVisible in interface Caret
        Returns:
        true if visible else false
        See Also:
        Caret.isVisible(), isActive()

      • setVisible

        public void setVisible(boolean e)
        Sets the caret visibility, and repaints the caret. It is important to understand the relationship between this method, isVisible and isActive. Calling this method with a value of true activates the caret blinking. Setting it to false turns it completely off. To determine whether the blinking is active, you should call isActive. In effect, isActive is an appropriate corresponding "getter" method for this one. isVisible can be used to fetch the current visibility status of the caret, meaning whether or not it is currently painted. This status will change as the caret blinks on and off.

        Here's a list showing the potential return values of both isActive and isVisible after calling this method:

        setVisible(true):

        • isActive(): true
        • isVisible(): true or false depending on whether or not the caret is blinked on or off

        setVisible(false):

        • isActive(): false
        • isVisible(): false
        Specified by:
        setVisible in interface Caret
        Parameters:
        e - the visibility specifier
        See Also:
        isActive(), Caret.setVisible(boolean)

      • setBlinkRate

        public void setBlinkRate(int rate)
        Sets the caret blink rate.
        Specified by:
        setBlinkRate in interface Caret
        Parameters:
        rate - the rate in milliseconds, 0 to stop blinking
        See Also:
        Caret.setBlinkRate(int)

      • getBlinkRate

        public int getBlinkRate()
        Gets the caret blink rate.
        Specified by:
        getBlinkRate in interface Caret
        Returns:
        the delay in milliseconds. If this is zero the caret will not blink.
        See Also:
        Caret.getBlinkRate()

      • getDot

        public int getDot()
        Fetches the current position of the caret.
        Specified by:
        getDot in interface Caret
        Returns:
        the position >= 0
        See Also:
        Caret.getDot()

      • getMark

        public int getMark()
        Fetches the current position of the mark. If there is a selection, the dot and mark will not be the same.
        Specified by:
        getMark in interface Caret
        Returns:
        the position >= 0
        See Also:
        Caret.getMark()

      • setDot

        public void setDot(int dot)
        Sets the caret position and mark to the specified position, with a forward bias. This implicitly sets the selection range to zero.
        Specified by:
        setDot in interface Caret
        Parameters:
        dot - the position >= 0
        See Also:
        setDot(int, Position.Bias), Caret.setDot(int)

      • moveDot

        public void moveDot(int dot,
                    Position.Bias dotBias)
        Moves the caret position to the specified position, with the specified bias.
        Parameters:
        dot - the position >= 0
        dotBias - the bias for this position, not null
        Throws:
        IllegalArgumentException - if the bias is null
        Since:
        1.6
        See Also:
        Caret.moveDot(int)

      • setDot

        public void setDot(int dot,
                   Position.Bias dotBias)
        Sets the caret position and mark to the specified position, with the specified bias. This implicitly sets the selection range to zero.
        Parameters:
        dot - the position >= 0
        dotBias - the bias for this position, not null
        Throws:
        IllegalArgumentException - if the bias is null
        Since:
        1.6
        See Also:
        Caret.setDot(int)

      • getDotBias

        public Position.Bias getDotBias()
        Returns the bias of the caret position.
        Returns:
        the bias of the caret position
        Since:
        1.6

      • getMarkBias

        public Position.Bias getMarkBias()
        Returns the bias of the mark.
        Returns:
        the bias of the mark
        Since:
        1.6

      • setMagicCaretPosition

        public void setMagicCaretPosition(Point p)
        Saves the current caret position. This is used when caret up/down actions occur, moving between lines that have uneven end positions.
        Specified by:
        setMagicCaretPosition in interface Caret
        Parameters:
        p - the position
        See Also:
        getMagicCaretPosition()

      • equals

        public boolean equals(Object obj)
        Compares this object to the specified object. The superclass behavior of comparing rectangles is not desired, so this is changed to the Object behavior.
        Overrides:
        equals in class Rectangle
        Parameters:
        obj - the object to compare this font with
        Returns:
        true if the objects are equal; false otherwise
        See Also:
        Object.hashCode(), HashMap

      • toString

        public String toString()
        Description copied from class: Rectangle
        Returns a String representing this Rectangle and its values.
        Overrides:
        toString in class Rectangle
        Returns:
        a String representing this Rectangle object's coordinate and size values.
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Java™ Platform
Standard Ed. 8

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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2022, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.

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