public class

GapContent

extends Object
implements Serializable AbstractDocument.Content
java.lang.Object
   ↳ javax.swing.text.GapContent

Class Overview

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.

Summary

Public Constructors
GapContent()
Creates a new GapContent object.
GapContent(int initialLength)
Creates a new GapContent object, with the initial size specified.
Public Methods
Position createPosition(int offset)
Creates a position within the content that will track change as the content is mutated.
void getChars(int where, int len, Segment chars)
Retrieves a portion of the content.
String getString(int where, int len)
Retrieves a portion of the content.
UndoableEdit insertString(int where, String str)
Inserts a string into the content.
int length()
Returns the length of the content.
UndoableEdit remove(int where, int nitems)
Removes part of the content.
Protected Methods
Object allocateArray(int len)
Allocate an array to store items of the type appropriate (which is determined by the subclass).
final Object getArray()
Access to the array.
int getArrayLength()
Get the length of the allocated array.
final int getGapEnd()
Access to the end of the gap.
final int getGapStart()
Access to the start of the gap.
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.
void replace(int position, int rmSize, Object addItems, int addSize)
Replace the given logical position in the storage with the given new items.
void resetMarksAtZero()
Resets all the marks that have an offset of 0 to have an index of zero as well.
void shiftEnd(int newSize)
Make the gap bigger, moving any necessary data and updating the appropriate marks
void shiftGap(int newGapStart)
Move the start of the gap to a new location, without changing the size of the gap.
void shiftGapEndUp(int newGapEnd)
Adjust the gap end upward.
void shiftGapStartDown(int newGapStart)
Adjust the gap end downward.
void updateUndoPositions(Vector positions, int offset, int length)
Resets the location for all the UndoPosRef instances in positions.
[Expand]
Inherited Methods
From class java.lang.Object
From interface javax.swing.text.AbstractDocument.Content

Public Constructors

public GapContent ()

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

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

Public Methods

public Position createPosition (int offset)

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

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

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
See Also

public String getString (int where, int len)

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
See Also

public UndoableEdit insertString (int where, String str)

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
See Also

public int length ()

Returns the length of the content.

Returns
  • the length >= 1
See Also

public UndoableEdit remove (int where, int nitems)

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
See Also

Protected Methods

protected Object allocateArray (int len)

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

protected final Object getArray ()

Access to the array. The actual type of the array is known only by the subclass.

protected int getArrayLength ()

Get the length of the allocated array.

protected final int getGapEnd ()

Access to the end of the gap.

protected final int getGapStart ()

Access to the start of the gap.

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

protected void replace (int position, int rmSize, Object addItems, int addSize)

Replace the given logical position in the storage with the given new items. This will move the gap to the area being changed if the gap is not currently located at the change location.

Parameters
position the location to make the replacement. This is not the location in the underlying storage array, but the location in the contiguous space being modeled.
rmSize the number of items to remove
addItems the new items to place in storage.

protected void resetMarksAtZero ()

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

protected void shiftEnd (int newSize)

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

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.

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).

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).

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