AsyncBoxView (Java Platform SE 8 )
Keywords: javax.swing.text.AsyncBoxView class
Date: 2026-04-24

javax.swing.text

## Class AsyncBoxView

- java.lang.Object
- - javax.swing.text.View
  - - javax.swing.text.AsyncBoxView

- All Implemented Interfaces:
    SwingConstants

      public class AsyncBoxView
      extends View

  A box that does layout asynchronously. This is useful to keep the GUI event thread moving by not doing any layout on it. The layout is done on a granularity of operations on the child views. After each child view is accessed for some part of layout (a potentially time consuming operation) the remaining tasks can be abandoned or a new higher priority task (i.e. to service a synchronous request or a visible area) can be taken on.

  While the child view is being accessed a read lock is acquired on the associated document so that the model is stable while being accessed.

  Since:
    1.3

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `class` | `AsyncBoxView.ChildLocator` A class to manage the effective position of the child views in a localized area while changes are being made around the localized area.
    `class` | `AsyncBoxView.ChildState` A record representing the layout state of a child view.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected AsyncBoxView.ChildLocator` | `locator` Object that manages the offsets of the children.

    - ### Fields inherited from class javax.swing.text.View

      `BadBreakWeight, ExcellentBreakWeight, ForcedBreakWeight, GoodBreakWeight, X_AXIS, Y_AXIS`

    - ### Fields inherited from interface javax.swing.SwingConstants

      `BOTTOM, CENTER, EAST, HORIZONTAL, LEADING, LEFT, NEXT, NORTH, NORTH_EAST, NORTH_WEST, PREVIOUS, RIGHT, SOUTH, SOUTH_EAST, SOUTH_WEST, TOP, TRAILING, VERTICAL, WEST`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `AsyncBoxView(Element elem, int axis)` Construct a box view that does asynchronous layout.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected AsyncBoxView.ChildState` | `createChildState(View v)` New ChildState records are created through this method to allow subclasses the extend the ChildState records to do/hold more
    `protected void` | `flushRequirementChanges()` Publish the changes in preferences upward to the parent view.
    `float` | `getBottomInset()` Get the bottom part of the margin around the view.
    `Shape` | `getChildAllocation(int index, Shape a)` Fetches the allocation for the given child view.
    `protected AsyncBoxView.ChildState` | `getChildState(int index)` Fetch the object representing the layout state of of the child at the given index.
    `protected boolean` | `getEstimatedMajorSpan()` Is the major span currently estimated?
    `protected float` | `getInsetSpan(int axis)` Fetch the span along an axis that is taken up by the insets.
    `protected LayoutQueue` | `getLayoutQueue()` Fetch the queue to use for layout.
    `float` | `getLeftInset()` Get the left part of the margin around the view.
    `int` | `getMajorAxis()` Fetch the major axis (the axis the children are tiled along).
    `float` | `getMaximumSpan(int axis)` Determines the maximum span for this view along an axis.
    `float` | `getMinimumSpan(int axis)` Determines the minimum span for this view along an axis.
    `int` | `getMinorAxis()` Fetch the minor axis (the axis orthogonal to the tiled axis).
    `int` | `getNextVisualPositionFrom(int pos, Position.Bias b, Shape a, int direction, Position.Bias[] biasRet)` Provides a way to determine the next visually represented model location that one might place a caret.
    `float` | `getPreferredSpan(int axis)` Determines the preferred span for this view along an axis.
    `float` | `getRightInset()` Get the right part of the margin around the view.
    `float` | `getTopInset()` Get the top part of the margin around the view.
    `View` | `getView(int n)` Gets the nth child view.
    `int` | `getViewCount()` Returns the number of views in this view.
    `int` | `getViewIndex(int pos, Position.Bias b)` Returns the child view index representing the given position in the model.
    `protected int` | `getViewIndexAtPosition(int pos, Position.Bias b)` Fetches the child view index representing the given position in the model.
    `protected void` | `loadChildren(ViewFactory f)` Loads all of the children to initialize the view.
    `protected void` | `majorRequirementChange(AsyncBoxView.ChildState cs, float delta)` Requirements changed along the major axis.
    `protected void` | `minorRequirementChange(AsyncBoxView.ChildState cs)` Requirements changed along the minor axis.
    `Shape` | `modelToView(int pos, Shape a, Position.Bias b)` Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it.
    `void` | `paint(Graphics g, Shape alloc)` Render the view using the given allocation and rendering surface.
    `void` | `preferenceChanged(View child, boolean width, boolean height)` Child views can call this on the parent to indicate that the preference has changed and should be reconsidered for layout.
    `void` | `replace(int offset, int length, View[] views)` Calls the superclass to update the child views, and updates the status records for the children.
    `void` | `setBottomInset(float i)` Set the bottom part of the margin around the view.
    `protected void` | `setEstimatedMajorSpan(boolean isEstimated)` Set the estimatedMajorSpan property that determines if the major span should be treated as being estimated.
    `void` | `setLeftInset(float i)` Set the left part of the margin around the view.
    `void` | `setParent(View parent)` Sets the parent of the view.
    `void` | `setRightInset(float i)` Set the right part of the margin around the view.
    `void` | `setSize(float width, float height)` Sets the size of the view.
    `void` | `setTopInset(float i)` Set the top part of the margin around the view.
    `protected void` | `updateLayout(DocumentEvent.ElementChange ec, DocumentEvent e, Shape a)` Update the layout in response to receiving notification of change from the model.
    `int` | `viewToModel(float x, float y, Shape a, Position.Bias[] biasReturn)` Provides a mapping from the view coordinate space to the logical coordinate space of the model.

    - ### Methods inherited from class javax.swing.text.View

      `append, breakView, changedUpdate, createFragment, forwardUpdate, forwardUpdateToView, getAlignment, getAttributes, getBreakWeight, getContainer, getDocument, getElement, getEndOffset, getGraphics, getParent, getResizeWeight, getStartOffset, getToolTipText, getViewFactory, getViewIndex, insert, insertUpdate, isVisible, modelToView, modelToView, remove, removeAll, removeUpdate, updateChildren, viewToModel`

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

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

- - ### Field Detail

    - #### locator

          protected AsyncBoxView.ChildLocator locator

      Object that manages the offsets of the children. All locking for management of child locations is on this object.

  - ### Constructor Detail

    - #### AsyncBoxView

          public AsyncBoxView(Element elem,
                              int axis)

      Construct a box view that does asynchronous layout.
      Parameters:
        `elem` - the element of the model to represent
        `axis` - the axis to tile along. This can be either X_AXIS or Y_AXIS.

  - ### Method Detail

    - #### getMajorAxis

          public int getMajorAxis()

      Fetch the major axis (the axis the children are tiled along). This will have a value of either X_AXIS or Y_AXIS.

    - #### getMinorAxis

          public int getMinorAxis()

      Fetch the minor axis (the axis orthogonal to the tiled axis). This will have a value of either X_AXIS or Y_AXIS.

    - #### getTopInset

          public float getTopInset()

      Get the top part of the margin around the view.

    - #### setTopInset

          public void setTopInset(float i)

      Set the top part of the margin around the view.
      Parameters:
        `i` - the value of the inset

    - #### getBottomInset

          public float getBottomInset()

      Get the bottom part of the margin around the view.

    - #### setBottomInset

          public void setBottomInset(float i)

      Set the bottom part of the margin around the view.
      Parameters:
        `i` - the value of the inset

    - #### getLeftInset

          public float getLeftInset()

      Get the left part of the margin around the view.

    - #### setLeftInset

          public void setLeftInset(float i)

      Set the left part of the margin around the view.
      Parameters:
        `i` - the value of the inset

    - #### getRightInset

          public float getRightInset()

      Get the right part of the margin around the view.

    - #### setRightInset

          public void setRightInset(float i)

      Set the right part of the margin around the view.
      Parameters:
        `i` - the value of the inset

    - #### getInsetSpan

          protected float getInsetSpan(int axis)

      Fetch the span along an axis that is taken up by the insets.
      Parameters:
        `axis` - the axis to determine the total insets along, either X_AXIS or Y_AXIS.
      Since:
        1.4

    - #### setEstimatedMajorSpan

          protected void setEstimatedMajorSpan(boolean isEstimated)

      Set the estimatedMajorSpan property that determines if the major span should be treated as being estimated. If this property is true, the value of setSize along the major axis will change the requirements along the major axis and incremental changes will be ignored until all of the children have been updated (which will cause the property to automatically be set to false). If the property is false the value of the majorSpan will be considered to be accurate and incremental changes will be added into the total as they are calculated.
      Since:
        1.4

    - #### getEstimatedMajorSpan

          protected boolean getEstimatedMajorSpan()

      Is the major span currently estimated?
      Since:
        1.4

    - #### getChildState

          protected AsyncBoxView.ChildState getChildState(int index)

      Fetch the object representing the layout state of of the child at the given index.
      Parameters:
        `index` - the child index. This should be a value >= 0 and < getViewCount().

    - #### getLayoutQueue

          protected LayoutQueue getLayoutQueue()

      Fetch the queue to use for layout.

    - #### createChildState

          protected AsyncBoxView.ChildState createChildState(View v)

      New ChildState records are created through this method to allow subclasses the extend the ChildState records to do/hold more

    - #### majorRequirementChange

          protected void majorRequirementChange(AsyncBoxView.ChildState cs,
                                                float delta)

      Requirements changed along the major axis. This is called by the thread doing layout for the given ChildState object when it has completed fetching the child views new preferences. Typically this would be the layout thread, but might be the event thread if it is trying to update something immediately (such as to perform a model/view translation).

      This is implemented to mark the major axis as having changed so that a future check to see if the requirements need to be published to the parent view will consider the major axis. If the span along the major axis is not estimated, it is updated by the given delta to reflect the incremental change. The delta is ignored if the major span is estimated.

    - #### minorRequirementChange

          protected void minorRequirementChange(AsyncBoxView.ChildState cs)

      Requirements changed along the minor axis. This is called by the thread doing layout for the given ChildState object when it has completed fetching the child views new preferences. Typically this would be the layout thread, but might be the GUI thread if it is trying to update something immediately (such as to perform a model/view translation).

    - #### flushRequirementChanges

          protected void flushRequirementChanges()

      Publish the changes in preferences upward to the parent view. This is normally called by the layout thread.

    - #### replace

          public void replace(int offset,
                              int length,
                              View[] views)

      Calls the superclass to update the child views, and updates the status records for the children. This is expected to be called while a write lock is held on the model so that interaction with the layout thread will not happen (i.e. the layout thread acquires a read lock before doing anything).
      Overrides:
        `replace` in class `View`
      Parameters:
        `offset` - the starting offset into the child views >= 0
        `length` - the number of existing views to replace >= 0
        `views` - the child views to insert

    - #### loadChildren

          protected void loadChildren(ViewFactory f)

      Loads all of the children to initialize the view. This is called by the `setParent` method. Subclasses can reimplement this to initialize their child views in a different manner. The default implementation creates a child view for each child element.

      Normally a write-lock is held on the Document while the children are being changed, which keeps the rendering and layout threads safe. The exception to this is when the view is initialized to represent an existing element (via this method), so it is synchronized to exclude preferenceChanged while we are initializing.

      Parameters:
        `f` - the view factory
      See Also:
        `setParent(javax.swing.text.View)`

    - #### getViewIndexAtPosition

          protected int getViewIndexAtPosition(int pos,
                                               Position.Bias b)

      Fetches the child view index representing the given position in the model. This is implemented to fetch the view in the case where there is a child view for each child element.
      Parameters:
        `pos` - the position >= 0
      Returns:
        index of the view representing the given position, or -1 if no view represents that position

    - #### updateLayout

          protected void updateLayout(DocumentEvent.ElementChange ec,
                                      DocumentEvent e,
                                      Shape a)

      Update the layout in response to receiving notification of change from the model. This is implemented to note the change on the ChildLocator so that offsets of the children will be correctly computed.
      Overrides:
        `updateLayout` in class `View`
      Parameters:
        `ec` - changes to the element this view is responsible for (may be null if there were no changes).
        `e` - the change information from the associated document
        `a` - the current allocation of the view
      See Also:
        `View.insertUpdate(javax.swing.event.DocumentEvent, java.awt.Shape, javax.swing.text.ViewFactory)`, `View.removeUpdate(javax.swing.event.DocumentEvent, java.awt.Shape, javax.swing.text.ViewFactory)`, `View.changedUpdate(javax.swing.event.DocumentEvent, java.awt.Shape, javax.swing.text.ViewFactory)`

    - #### setParent

          public void setParent(View parent)

      Sets the parent of the view. This is reimplemented to provide the superclass behavior as well as calling the `loadChildren` method if this view does not already have children. The children should not be loaded in the constructor because the act of setting the parent may cause them to try to search up the hierarchy (to get the hosting Container for example). If this view has children (the view is being moved from one place in the view hierarchy to another), the `loadChildren` method will not be called.
      Overrides:
        `setParent` in class `View`
      Parameters:
        `parent` - the parent of the view, null if none

    - #### preferenceChanged

          public void preferenceChanged(View child,
                                        boolean width,
                                        boolean height)

      Child views can call this on the parent to indicate that the preference has changed and should be reconsidered for layout. This is reimplemented to queue new work on the layout thread. This method gets messaged from multiple threads via the children.
      Overrides:
        `preferenceChanged` in class `View`
      Parameters:
        `child` - the child view
        `width` - true if the width preference has changed
        `height` - true if the height preference has changed
      See Also:
        `JComponent.revalidate()`

    - #### setSize

          public void setSize(float width,
                              float height)

      Sets the size of the view. This should cause layout of the view if the view caches any layout information.

      Since the major axis is updated asynchronously and should be the sum of the tiled children the call is ignored for the major axis. Since the minor axis is flexible, work is queued to resize the children if the minor span changes.

      Overrides:
        `setSize` in class `View`
      Parameters:
        `width` - the width >= 0
        `height` - the height >= 0

    - #### paint

          public void paint(Graphics g,
                            Shape alloc)

      Render the view using the given allocation and rendering surface.

      This is implemented to determine whether or not the desired region to be rendered (i.e. the unclipped area) is up to date or not. If up-to-date the children are rendered. If not up-to-date, a task to build the desired area is placed on the layout queue as a high priority task. This keeps by event thread moving by rendering if ready, and postponing until a later time if not ready (since paint requests can be rescheduled).

      Specified by:
        `paint` in class `View`
      Parameters:
        `g` - the rendering surface to use
        `alloc` - the allocated region to render into
      See Also:
        `View.paint(java.awt.Graphics, java.awt.Shape)`

    - #### getPreferredSpan

          public float getPreferredSpan(int axis)

      Determines the preferred span for this view along an axis.
      Specified by:
        `getPreferredSpan` in class `View`
      Parameters:
        `axis` - may be either View.X_AXIS or View.Y_AXIS
      Returns:
        the span the view would like to be rendered into >= 0. Typically the view is told to render into the span that is returned, although there is no guarantee. The parent may choose to resize or break the view.
      Throws:
        `IllegalArgumentException` - for an invalid axis type
      See Also:
        `View.getPreferredSpan(int)`

    - #### getMinimumSpan

          public float getMinimumSpan(int axis)

      Determines the minimum span for this view along an axis.
      Overrides:
        `getMinimumSpan` in class `View`
      Parameters:
        `axis` - may be either View.X_AXIS or View.Y_AXIS
      Returns:
        the span the view would like to be rendered into >= 0. Typically the view is told to render into the span that is returned, although there is no guarantee. The parent may choose to resize or break the view.
      Throws:
        `IllegalArgumentException` - for an invalid axis type
      See Also:
        `View.getPreferredSpan(int)`

    - #### getMaximumSpan

          public float getMaximumSpan(int axis)

      Determines the maximum span for this view along an axis.
      Overrides:
        `getMaximumSpan` in class `View`
      Parameters:
        `axis` - may be either View.X_AXIS or View.Y_AXIS
      Returns:
        the span the view would like to be rendered into >= 0. Typically the view is told to render into the span that is returned, although there is no guarantee. The parent may choose to resize or break the view.
      Throws:
        `IllegalArgumentException` - for an invalid axis type
      See Also:
        `View.getPreferredSpan(int)`

    - #### getViewCount

          public int getViewCount()

      Returns the number of views in this view. Since the default is to not be a composite view this returns 0.
      Overrides:
        `getViewCount` in class `View`
      Returns:
        the number of views >= 0
      See Also:
        `View.getViewCount()`

    - #### getView

          public View getView(int n)

      Gets the nth child view. Since there are no children by default, this returns null.
      Overrides:
        `getView` in class `View`
      Parameters:
        `n` - the number of the view to get, >= 0 && < getViewCount()
      Returns:
        the view

    - #### getChildAllocation

          public Shape getChildAllocation(int index,
                                          Shape a)

      Fetches the allocation for the given child view. This enables finding out where various views are located, without assuming the views store their location. This returns null since the default is to not have any child views.
      Overrides:
        `getChildAllocation` in class `View`
      Parameters:
        `index` - the index of the child, >= 0 && < getViewCount()
        `a` - the allocation to this view.
      Returns:
        the allocation to the child

    - #### getViewIndex

          public int getViewIndex(int pos,
                                  Position.Bias b)

      Returns the child view index representing the given position in the model. By default a view has no children so this is implemented to return -1 to indicate there is no valid child index for any position.
      Overrides:
        `getViewIndex` in class `View`
      Parameters:
        `pos` - the position >= 0
      Returns:
        index of the view representing the given position, or -1 if no view represents that position
      Since:
        1.3

    - #### modelToView

          public Shape modelToView(int pos,
                                   Shape a,
                                   Position.Bias b)
                            throws BadLocationException

      Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it.
      Specified by:
        `modelToView` in class `View`
      Parameters:
        `pos` - the position to convert >= 0
        `a` - the allocated region to render into
        `b` - the bias toward the previous character or the next character represented by the offset, in case the position is a boundary of two views.
      Returns:
        the bounding box of the given position is returned
      Throws:
        `BadLocationException` - if the given position does not represent a valid location in the associated document
        `IllegalArgumentException` - for an invalid bias argument
      See Also:
        `View.viewToModel(float, float, java.awt.Shape, javax.swing.text.Position.Bias[])`

    - #### viewToModel

          public int viewToModel(float x,
                                 float y,
                                 Shape a,
                                 Position.Bias[] biasReturn)

      Provides a mapping from the view coordinate space to the logical coordinate space of the model. The biasReturn argument will be filled in to indicate that the point given is closer to the next character in the model or the previous character in the model.

      This is expected to be called by the GUI thread, holding a read-lock on the associated model. It is implemented to locate the child view and determine it's allocation with a lock on the ChildLocator object, and to call viewToModel on the child view with a lock on the ChildState object to avoid interaction with the layout thread.

      Specified by:
        `viewToModel` in class `View`
      Parameters:
        `x` - the X coordinate >= 0
        `y` - the Y coordinate >= 0
        `a` - the allocated region to render into
      Returns:
        the location within the model that best represents the given point in the view >= 0. The biasReturn argument will be filled in to indicate that the point given is closer to the next character in the model or the previous character in the model.

    - #### getNextVisualPositionFrom

          public int getNextVisualPositionFrom(int pos,
                                               Position.Bias b,
                                               Shape a,
                                               int direction,
                                               Position.Bias[] biasRet)
                                        throws BadLocationException

      Provides a way to determine the next visually represented model location that one might place a caret. Some views may not be visible, they might not be in the same order found in the model, or they just might not allow access to some of the locations in the model. This method enables specifying a position to convert within the range of >=0. If the value is -1, a position will be calculated automatically. If the value < -1, the `BadLocationException` will be thrown.
      Overrides:
        `getNextVisualPositionFrom` in class `View`
      Parameters:
        `pos` - the position to convert
        `a` - the allocated region to render into
        `direction` - the direction from the current position that can be thought of as the arrow keys typically found on a keyboard; this may be one of the following:
        - `SwingConstants.WEST`
        - `SwingConstants.EAST`
        - `SwingConstants.NORTH`
        - `SwingConstants.SOUTH`
        `biasRet` - an array contain the bias that was checked
      Returns:
        the location within the model that best represents the next location visual position
      Throws:
        `BadLocationException` - the given position is not a valid position within the document
        `IllegalArgumentException` - if `direction` is invalid

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