Package aQute.bnd.properties

Class GapTextStore

java.lang.Object
aQute.bnd.properties.GapTextStore
All Implemented Interfaces:
ITextStore
public class GapTextStore extends Object implements ITextStore
Implements a gap managing text store. The gap text store relies on the assumption that consecutive changes to a document are co-located. The start of the gap is always moved to the location of the last change.

Performance: Typing-style changes perform in constant time unless re-allocation becomes necessary. Generally, a change that does not cause re-allocation will cause at most one arraycopy operation of a length of about d, where d is the distance from the previous change. Let a(x) be the algorithmic performance of an arraycopy operation of the length x , then such a change then performs in O(a(x)), get(int, length) performs in O(a(length)), get(int) in O(1).

How frequently the array needs re-allocation is controlled by the constructor parameters.

This class is not intended to be subclassed.

See Also:

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private char[]
    fContent
    The store's content
    private int
    fGapEnd
    End index of the gap
    private int
    fGapStart
    Starting index of the gap
    private final int
    fMaxGapSize
    The maximum gap size allocated when re-allocation occurs.
    private final int
    fMinGapSize
    The minimum gap size allocated when re-allocation occurs.
    private final float
    fSizeMultiplier
    The multiplier to compute the array size from the content length (1 <= fSizeMultiplier <= 2).
    private int
    fThreshold
    The current high water mark.

  • Constructor Summary

    Constructors
    Constructor
    Description
    GapTextStore()
    Equivalent to new GapTextStore(256, 4096, 0.1f).
    GapTextStore(int lowWatermark, int highWatermark)
    Creates a new empty text store using the specified low and high watermarks.
    GapTextStore(int minSize, int maxSize, float maxGapFactor)
    Creates an empty text store that uses re-allocation thresholds relative to the content length.

  • Method Summary

    Modifier and Type
    Method
    Description
    private void
    adjustGap(int offset, int remove, int add)
    Moves the gap to offset + add, moving any content after offset + remove behind the gap.
    private char[]
    allocate(int size)
    Allocates a new char[size].
    private void
    arrayCopy(int srcPos, char[] dest, int destPos, int length)
     
    private int
    gapSize()
    Returns the gap size.
    final char
    get(int offset)
    Returns the character at the specified offset.
    final String
    get(int offset, int length)
    Returns the text of the specified character range.
    protected String
    getContentAsString()
    Returns a copy of the content of this text store.
    protected int
    getGapEndIndex()
    Returns the end index of the gap managed by this text store.
    protected int
    getGapStartIndex()
    Returns the start index of the gap managed by this text store.
    final int
    getLength()
    Returns number of characters stored in this text store.
    private int
    moveGap(int offset, int remove, int oldGapSize, int newGapSize, int newGapStart)
    Moves the gap to newGapStart.
    private int
    reallocate(int offset, int remove, int oldGapSize, int newGapSize, int newGapStart)
    Reallocates a new array and copies the data from the previous one.
    final void
    replace(int offset, int length, String text)
    Replaces the specified character range with the given text.
    final void
    set(String text)
    Replace the content of the text store with the given text.

    Methods inherited from class java.lang.Object

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

  • Field Details

    • fMinGapSize

      private final int fMinGapSize
      The minimum gap size allocated when re-allocation occurs. @since 3.3

    • fMaxGapSize

      private final int fMaxGapSize
      The maximum gap size allocated when re-allocation occurs. @since 3.3

    • fSizeMultiplier

      private final float fSizeMultiplier
      The multiplier to compute the array size from the content length (1 <= fSizeMultiplier <= 2). @since 3.3

    • fContent

      private char[] fContent
      The store's content

    • fGapStart

      private int fGapStart
      Starting index of the gap

    • fGapEnd

      private int fGapEnd
      End index of the gap

    • fThreshold

      private int fThreshold
      The current high water mark. If a change would cause the gap to grow larger than this, the array is re-allocated. @since 3.3

  • Constructor Details

    • GapTextStore

      public GapTextStore(int lowWatermark, int highWatermark)
      Creates a new empty text store using the specified low and high watermarks.
      Parameters:
      lowWatermark - unused - at the lower bound, the array is only resized when the content does not fit
      highWatermark - if the gap is ever larger than this, it will automatically be shrunken (>= 0) @deprecated use GapTextStore(int, int, float) instead

    • GapTextStore

      public GapTextStore()
      Equivalent to new GapTextStore(256, 4096, 0.1f). @since 3.3

    • GapTextStore

      public GapTextStore(int minSize, int maxSize, float maxGapFactor)
      Creates an empty text store that uses re-allocation thresholds relative to the content length. Re-allocation is controlled by the gap factor, which is the quotient of the gap size and the array size. Re-allocation occurs if a change causes the gap factor to go outside [0, maxGapFactor]. When re-allocation occurs, the array is sized such that the gap factor is 0.5 * maxGapFactor. The gap size computed in this manner is bounded by the minSize and maxSize parameters.

      A maxGapFactor of 0 creates a text store that never has a gap at all (if minSize is 0); a maxGapFactor of 1 creates a text store that doubles its size with every re-allocation and that never shrinks.

      The minSize and maxSize parameters are absolute bounds to the allocated gap size. Use minSize to avoid frequent re-allocation for small documents. Use maxSize to avoid a huge gap being allocated for large documents.

      Parameters:
      minSize - the minimum gap size to allocate (>= 0; use 0 for no minimum)
      maxSize - the maximum gap size to allocate (>= minSize; use Integer.MAX_VALUE for no maximum)
      maxGapFactor - is the maximum fraction of the array that is occupied by the gap ( 0 <= maxGapFactor <= 1 ) @since 3.3

  • Method Details

    • get

      public final char get(int offset)
      Description copied from interface: ITextStore
      Returns the character at the specified offset.
      Specified by:
      get in interface ITextStore
      Parameters:
      offset - the offset in this text store
      Returns:
      the character at this offset

    • get

      public final String get(int offset, int length)
      Description copied from interface: ITextStore
      Returns the text of the specified character range.
      Specified by:
      get in interface ITextStore
      Parameters:
      offset - the offset of the range
      length - the length of the range
      Returns:
      the text of the range

    • getLength

      public final int getLength()
      Description copied from interface: ITextStore
      Returns number of characters stored in this text store.
      Specified by:
      getLength in interface ITextStore
      Returns:
      the number of characters stored in this text store

    • set

      public final void set(String text)
      Description copied from interface: ITextStore
      Replace the content of the text store with the given text. Convenience method for replace(0, getLength(), text.
      Specified by:
      set in interface ITextStore
      Parameters:
      text - the new content of the text store

    • replace

      public final void replace(int offset, int length, String text)
      Description copied from interface: ITextStore
      Replaces the specified character range with the given text. replace(getLength(), 0, "some text") is a valid call and appends text to the end of the text store.
      Specified by:
      replace in interface ITextStore
      Parameters:
      offset - the offset of the range to be replaced
      length - the number of characters to be replaced
      text - the substitution text

    • adjustGap

      private void adjustGap(int offset, int remove, int add)
      Moves the gap to offset + add, moving any content after offset + remove behind the gap. The gap size is kept between 0 and fThreshold, leading to re-allocation if needed. The content between offset and offset + add is undefined after this operation.
      Parameters:
      offset - the offset at which a change happens
      remove - the number of character which are removed or overwritten at offset
      add - the number of character which are inserted or overwriting at offset

    • moveGap

      private int moveGap(int offset, int remove, int oldGapSize, int newGapSize, int newGapStart)
      Moves the gap to newGapStart.
      Parameters:
      offset - the change offset
      remove - the number of removed / overwritten characters
      oldGapSize - the old gap size
      newGapSize - the gap size after the change
      newGapStart - the offset in the array to move the gap to
      Returns:
      the new gap end @since 3.3

    • reallocate

      private int reallocate(int offset, int remove, int oldGapSize, int newGapSize, int newGapStart)
      Reallocates a new array and copies the data from the previous one.
      Parameters:
      offset - the change offset
      remove - the number of removed / overwritten characters
      oldGapSize - the old gap size
      newGapSize - the gap size after the change if no re-allocation would occur (can be negative)
      newGapStart - the offset in the array to move the gap to
      Returns:
      the new gap end @since 3.3

    • allocate

      private char[] allocate(int size)
      Allocates a new char[size].
      Parameters:
      size - the length of the new array.
      Returns:
      a newly allocated char array @since 3.3

    • arrayCopy

      private void arrayCopy(int srcPos, char[] dest, int destPos, int length)

    • gapSize

      private int gapSize()
      Returns the gap size.
      Returns:
      the gap size @since 3.3

    • getContentAsString

      protected String getContentAsString()
      Returns a copy of the content of this text store. For internal use only.
      Returns:
      a copy of the content of this text store

    • getGapStartIndex

      protected int getGapStartIndex()
      Returns the start index of the gap managed by this text store. For internal use only.
      Returns:
      the start index of the gap managed by this text store

    • getGapEndIndex

      protected int getGapEndIndex()
      Returns the end index of the gap managed by this text store. For internal use only.
      Returns:
      the end index of the gap managed by this text store