javax.swing.text
class GapContent

All Implemented Interfaces:

Serializable, AbstractDocument.Content

public class GapContent
extends GapVector
implements AbstractDocument.Content, Serializable

An implementation of the AbstractDocument.Content interface implemented using a gapped buffer similar to that used by emacs. The underlying storage is a array of unicode characters with a gap somewhere. The gap is moved to the location of changes to take advantage of common behavior where most changes are in the same location. Changes that occur at a gap boundary are generally cheap and moving the gap is generally cheaper than moving the array contents directly to accomodate the change.

The positions tracking change are also generally cheap to maintain. The Position implementations (marks) store the array index and can easily calculate the sequential position from the current gap location. Changes only require update to the the marks between the old and new gap boundaries when the gap is moved, so generally updating the marks is pretty cheap. The marks are stored sorted so they can be located quickly with a binary search. This increases the cost of adding a mark, and decreases the cost of keeping the mark updated.

GapContent

public GapContent()

Creates a new GapContent object. Initial size defaults to 10.

GapContent

public GapContent(int initialLength)

Creates a new GapContent object, with the initial size specified. The initial size will not be allowed to go below 2, to give room for the implied break and the gap.

Parameters:

initialLength - the initial size

allocateArray

protected Object allocateArray(int len)

Allocate an array to store items of the type appropriate (which is determined by the subclass).

Overrides:

allocateArray in class GapVector

Parameters:

len

createPosition

public Position createPosition(int offset)
                        throws BadLocationException

Creates a position within the content that will track change as the content is mutated.

Parameters:

offset - the offset to track >= 0

Returns:

the position

Throws:

BadLocationException - if the specified position is invalid

getArrayLength

protected int getArrayLength()

Get the length of the allocated array.

Overrides:

getArrayLength in class GapVector

getChars

public void getChars(int where,
                     int len,
                     Segment chars)
              throws BadLocationException

Retrieves a portion of the content. If the desired content spans the gap, we copy the content. If the desired content does not span the gap, the actual store is returned to avoid the copy since it is contiguous.

Parameters:

where - the starting position >= 0, where + len <= length()

len - the number of characters to retrieve >= 0

chars - the Segment object to return the characters in

Throws:

BadLocationException - if the specified position is invalid

getPositionsInRange

protected Vector getPositionsInRange(Vector v,
                                     int offset,
                                     int length)

Returns a Vector containing instances of UndoPosRef for the Positions in the range offset to offset + length. If v is not null the matching Positions are placed in there. The vector with the resulting Positions are returned.

Parameters:

v - the Vector to use, with a new one created on null

offset - the starting offset >= 0

length - the length >= 0

Returns:

the set of instances

getString

public String getString(int where,
                        int len)
                 throws BadLocationException

Retrieves a portion of the content.

Parameters:

where - the starting position >= 0

len - the length to retrieve >= 0

Returns:

a string representing the content

Throws:

BadLocationException - if the specified position is invalid

insertString

public UndoableEdit insertString(int where,
                                 String str)
                          throws BadLocationException

Inserts a string into the content.

Parameters:

where - the starting position >= 0, < length()

str - the non-null string to insert

Returns:

an UndoableEdit object for undoing

Throws:

BadLocationException - if the specified position is invalid

length

public int length()

Returns the length of the content.

Returns:

the length >= 1

remove

public UndoableEdit remove(int where,
                           int nitems)
                    throws BadLocationException

Removes part of the content.

Parameters:

where - the starting position >= 0, where + nitems < length()

nitems - the number of characters to remove >= 0

Returns:

an UndoableEdit object for undoing

Throws:

BadLocationException - if the specified position is invalid

resetMarksAtZero

protected void resetMarksAtZero()

Resets all the marks that have an offset of 0 to have an index of zero as well.

shiftEnd

protected void shiftEnd(int newSize)

Make the gap bigger, moving any necessary data and updating the appropriate marks

Overrides:

shiftEnd in class GapVector

Parameters:

newSize

shiftGap

protected void shiftGap(int newGapStart)

Move the start of the gap to a new location, without changing the size of the gap. This moves the data in the array and updates the marks accordingly.

Overrides:

shiftGap in class GapVector

Parameters:

newGapStart

shiftGapEndUp

protected void shiftGapEndUp(int newGapEnd)

Adjust the gap end upward. This doesn't move any data, but it does update any marks affected by the boundary change. All marks from the old gap end up to the new gap end are squeezed to the end of the gap (their location has been removed).

Overrides:

shiftGapEndUp in class GapVector

Parameters:

newGapEnd

shiftGapStartDown

protected void shiftGapStartDown(int newGapStart)

Adjust the gap end downward. This doesn't move any data, but it does update any marks affected by the boundary change. All marks from the old gap start down to the new gap start are squeezed to the end of the gap (their location has been removed).

Overrides:

shiftGapStartDown in class GapVector

Parameters:

newGapStart

updateUndoPositions

protected void updateUndoPositions(Vector positions,
                                   int offset,
                                   int length)

Resets the location for all the UndoPosRef instances in positions.

This is meant for internal usage, and is generally not of interest to subclasses.

Parameters:

positions - the UndoPosRef instances to reset

offset

length