java.lang.Object
javax.swing.text.GapContent
- All Implemented Interfaces:
Serializable,AbstractDocument.Content
An implementation of the AbstractDocument.Content interface
implemented using a gapped buffer similar to that used by emacs.
The underlying storage is an 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 accommodate 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 updating 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.
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Constructor Summary
ConstructorsConstructorDescriptionCreates a new GapContent object.GapContent(int initialLength) Creates a new GapContent object, with the initial size specified. -
Method Summary
Modifier and TypeMethodDescriptionprotected ObjectallocateArray(int len) Allocate an array to store items of the type appropriate (which is determined by the subclass).createPosition(int offset) Creates a position within the content that will track change as the content is mutated.protected final ObjectgetArray()Access to the array.protected intGet the length of the allocated array.voidRetrieves a portion of the content.protected final intAccess to the end of the gap.protected final intAccess to the start of the gap.protected VectorgetPositionsInRange(Vector v, int offset, int length) Returns a Vector containing instances of UndoPosRef for the Positions in the rangeoffsettooffset+length.getString(int where, int len) Retrieves a portion of the content.insertString(int where, String str) Inserts a string into the content.intlength()Returns the length of the content.remove(int where, int nitems) Removes part of the content.protected voidReplace the given logical position in the storage with the given new items.protected voidResets all the marks that have an offset of 0 to have an index of zero as well.protected voidshiftEnd(int newSize) Make the gap bigger, moving any necessary data and updating the appropriate marksprotected voidshiftGap(int newGapStart) Move the start of the gap to a new location, without changing the size of the gap.protected voidshiftGapEndUp(int newGapEnd) Adjust the gap end upward.protected voidshiftGapStartDown(int newGapStart) Adjust the gap end downward.protected voidupdateUndoPositions(Vector positions, int offset, int length) Resets the location for all the UndoPosRef instances inpositions.
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Constructor Details
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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
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Method Details
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allocateArray
Allocate an array to store items of the type appropriate (which is determined by the subclass).- Parameters:
len- the length of the array- Returns:
- the java array of some type
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getArrayLength
protected int getArrayLength()Get the length of the allocated array.- Returns:
- the length of the array
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length
public int length()Returns the length of the content.- Specified by:
lengthin interfaceAbstractDocument.Content- Returns:
- the length >= 1
- See Also:
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insertString
Inserts a string into the content.- Specified by:
insertStringin interfaceAbstractDocument.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:
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remove
Removes part of the content.- Specified by:
removein interfaceAbstractDocument.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:
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getString
Retrieves a portion of the content.- Specified by:
getStringin interfaceAbstractDocument.Content- Parameters:
where- the starting position >= 0len- the length to retrieve >= 0- Returns:
- a string representing the content
- Throws:
BadLocationException- if the specified position is invalid- See Also:
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getChars
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.- Specified by:
getCharsin interfaceAbstractDocument.Content- Parameters:
where- the starting position >= 0, where + len <= length()len- the number of characters to retrieve >= 0chars- the Segment object to return the characters in- Throws:
BadLocationException- if the specified position is invalid- See Also:
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createPosition
Creates a position within the content that will track change as the content is mutated.- Specified by:
createPositionin interfaceAbstractDocument.Content- Parameters:
offset- the offset to track >= 0- Returns:
- the position
- Throws:
BadLocationException- if the specified position is invalid
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shiftEnd
protected void shiftEnd(int newSize) Make the gap bigger, moving any necessary data and updating the appropriate marks- Parameters:
newSize- the new capacity
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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.- Parameters:
newGapStart- the new start of the gap
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resetMarksAtZero
protected void resetMarksAtZero()Resets all the marks that have an offset of 0 to have an index of zero as well. -
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).- Parameters:
newGapStart- the new start of the gap
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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).- Parameters:
newGapEnd- the new end of the gap
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getPositionsInRange
Returns a Vector containing instances of UndoPosRef for the Positions in the rangeoffsettooffset+length. Ifvis 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 nulloffset- the starting offset >= 0length- the length >= 0- Returns:
- the set of instances
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updateUndoPositions
Resets the location for all the UndoPosRef instances inpositions.This is meant for internal usage, and is generally not of interest to subclasses.
- Parameters:
positions- the UndoPosRef instances to resetoffset- where the string was insertedlength- length of inserted string
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getArray
Access to the array. The actual type of the array is known only by the subclass.- Returns:
- the java array of some type
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getGapStart
protected final int getGapStart()Access to the start of the gap.- Returns:
- the start of the gap
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getGapEnd
protected final int getGapEnd()Access to the end of the gap.- Returns:
- the end of the gap
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replace
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 removeaddItems- the new items to place in storage.addSize- the number of items to add
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