net.sf.saxon.str

Class ZenoString

java.lang.Object

net.sf.saxon.str.UnicodeString

net.sf.saxon.str.ZenoString

All Implemented Interfaces:

java.lang.Comparable<UnicodeString>, AtomicMatchKey

public class ZenoString
extends UnicodeString

A ZenoString is an implementation of UnicodeString that comprises a list of segments representing substrings of the total string. By convention the segments are not themselves ZenoStrings, so the structure is a shallow tree. An index holds pointers to the segments and their offsets within the string as a whole; this is used to locate the codepoint at any particular location in the string.

The segments will always be non-empty. An empty string contains no segments.

The key to the performance of the data structure (and its name) is the algorithm for consolidating segments when strings are concatenated, so as to keep the number of segments increasing logarithmically with the string size, with short segments at the extremities to allow efficient further concatenation at the ends.

For further details see the paper by Michael Kay at Balisage 2021.

Field Summary

Fields

Modifier and Type	Field and Description
static ZenoString	EMPTY An empty ZenoString

Method Summary

Modifier and Type	Method and Description
int	codePointAt(long index) Get the code point at a given position in the string
IntIterator	codePoints() Get an iterator over the code points present in the string.
ZenoString	concat(UnicodeString other) Concatenate another string
static UnicodeString	concatSegments(UnicodeString left, UnicodeString right)
java.util.List<java.lang.Long>	debugSegmentLengths() This method is for diagnostics and unit testing only: it exposes the lengths of the internal segments.
UnicodeString	economize() Get an equivalent UnicodeString that uses the most economical representation available
int	getWidth() Get the number of bits needed to hold all the characters in this string
long	indexOf(int codePoint, long from) Get the position of the first occurrence of the specified codepoint, starting the search at a given position in the string
long	indexWhere(java.util.function.IntPredicate predicate, long from) Get the position of the first occurrence of a codepoint that matches a supplied predicate, starting the search at a given position in the string
boolean	isEmpty() Ask whether the string is empty
long	length() Get the length of the string
static ZenoString	of(UnicodeString content) Construct a ZenoString from a supplied UnicodeString
UnicodeString	substring(long start, long end) Get a substring of this codepoint sequence, with a given start and end position
java.lang.String	toString()
void	writeSegments(UnicodeWriter writer) Write each of the segments in turn to a UnicodeWriter

Methods inherited from class net.sf.saxon.str.UnicodeString

asAtomic, checkSubstringBounds, compareTo, equals, estimatedLength, hashCode, hasSubstring, indexOf, indexOf, length32, prefix, requireInt, substring, tidy, verifyCharacters

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

EMPTY

public static final ZenoString EMPTY

An empty ZenoString

Method Detail

of

public static ZenoString of(UnicodeString content)

Construct a ZenoString from a supplied UnicodeString

Parameters:

content - the supplied UnicodeString

Returns:

the resulting ZenoString

codePoints

public IntIterator codePoints()

Get an iterator over the code points present in the string.

Specified by:

codePoints in class UnicodeString

Returns:

an iterator that delivers the individual code points

length

public long length()

Get the length of the string

Specified by:

length in class UnicodeString

Returns:

the number of code points in the string

isEmpty

public boolean isEmpty()

Ask whether the string is empty

Overrides:

isEmpty in class UnicodeString

Returns:

true if the length of the string is zero

getWidth

public int getWidth()

Get the number of bits needed to hold all the characters in this string

Specified by:

getWidth in class UnicodeString

Returns:

7 for ascii characters, 8 for latin-1, 16 for BMP, 24 for general Unicode.

indexOf

public long indexOf(int codePoint,
                    long from)

Get the position of the first occurrence of the specified codepoint, starting the search at a given position in the string

Specified by:

indexOf in class UnicodeString

Parameters:

codePoint - the sought codePoint

from - the position from which the search should start (0-based), in the range 0 to length()-1

Returns:

the position (0-based) of the first occurrence found, or -1 if not found

Throws:

java.lang.IndexOutOfBoundsException - if the from value is out of range

indexWhere

public long indexWhere(java.util.function.IntPredicate predicate,
                       long from)

Description copied from class: UnicodeString

Get the position of the first occurrence of a codepoint that matches a supplied predicate, starting the search at a given position in the string

Overrides:

indexWhere in class UnicodeString

Parameters:

predicate - condition that the codepoint must satisfy

from - the position from which the search should start (0-based)

Returns:

the position (0-based) of the first codepoint to match the predicate, or -1 if not found

codePointAt

public int codePointAt(long index)

Get the code point at a given position in the string

Specified by:

codePointAt in class UnicodeString

Parameters:

index - the given position (0-based)

Returns:

the code point at the given position

Throws:

java.lang.IndexOutOfBoundsException - if the index is out of range

substring

public UnicodeString substring(long start,
                               long end)

Get a substring of this codepoint sequence, with a given start and end position

Specified by:

substring in class UnicodeString

Parameters:

start - the start position (0-based): that is, the position of the first code point to be included

end - the end position (0-based): specifically, the position of the first code point not to be included

Returns:

the requested substring

concat

public ZenoString concat(UnicodeString other)

Concatenate another string

Overrides:

concat in class UnicodeString

Parameters:

other - the string to be appended to this one

Returns:

the result of the concatenation (neither input string is altered)

writeSegments

public void writeSegments(UnicodeWriter writer)
                   throws java.io.IOException

Write each of the segments in turn to a UnicodeWriter

Parameters:

writer - the writer to which the string is to be written

Throws:

java.io.IOException

concatSegments

public static UnicodeString concatSegments(UnicodeString left,
                                           UnicodeString right)

economize

public UnicodeString economize()

Get an equivalent UnicodeString that uses the most economical representation available

Overrides:

economize in class UnicodeString

Returns:

an equivalent UnicodeString

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

debugSegmentLengths

public java.util.List<java.lang.Long> debugSegmentLengths()

This method is for diagnostics and unit testing only: it exposes the lengths of the internal segments. This is an implementation detail that is subject to change and does not affect the exposed functionality.

Returns:

the lengths of the segments