Package org.basex.query.value.seq

Class Empty

java.lang.Object

org.basex.query.expr.ExprInfo

org.basex.query.expr.Expr

org.basex.query.value.Value

org.basex.query.value.item.Item

org.basex.query.value.seq.Empty

All Implemented Interfaces:

Iterable<Item>

public final class Empty
extends Item

Empty sequence.

Author:

BaseX Team 2005-21, BSD License, Christian Gruen

Field Summary

Fields

Modifier and Type	Field	Description
static final BasicIter<Item>	ITER	Empty iterator.
static final Empty	VALUE	Single instance.

Fields inherited from class org.basex.query.value.item.Item

UNDEF

Fields inherited from class org.basex.query.value.Value

type

Method Summary

Modifier and Type	Method	Description
Iter	atomIter(QueryContext qc, InputInfo ii)	Evaluates the expression and returns an iterator on the resulting, atomized items.
long	atomSize()	Computes the number of atomized items.
String	description()	Returns a string description of the expression.
Item	ebv(QueryContext qc, InputInfo ii)	Checks if the effective boolean value can be computed for this expression:
boolean	eq(Item item, Collation coll, StaticContext sc, InputInfo ii)	Compares the items for equality.
boolean	equals(Object obj)	This function is e.g.
int	hash(InputInfo ii)	Returns a hash code for this value.
BasicIter<Item>	iter()	Returns an iterator.
void	plan(QueryPlan plan)	Creates a query plan.
void	plan(QueryString qs)	Creates a query string.
SeqType	seqType()	Returns the static type of the resulting value.
Expr	simplifyFor(CompileContext.Simplify mode, CompileContext cc)	This function is called at compile time for expressions whose operands might be simplified.
long	size()	Returns the result size, or -1 if the size is unknown.
byte[]	string(InputInfo ii)	Returns a string representation of the value.
Empty	subsequence(long start, long length, QueryContext qc)	Returns a subsequence of this value with the given start and length.
Item	test(QueryContext qc, InputInfo ii)	Performs a predicate test and returns the item if the test was successful.
Object	toJava()	Returns a Java representation of the value.
boolean	vacuous()	Tests if this is a vacuous expression (empty sequence or error function).

Methods inherited from class org.basex.query.value.item.Item

atomItem, atomValue, bool, cache, comparable, dbl, ddo, dec, diff, equiv, flt, input, instanceOf, item, itemAt, itr, materialize, persistent, refineType, reverse, sameKey, score, typeId, xdmInfo

Methods inherited from class org.basex.query.value.Value

accept, checkUp, compile, copy, count, exprSize, has, inline, inlineable, isEmpty, isItem, iter, iterator, materialize, serialize, serialize, serialize, value

Methods inherited from class org.basex.query.expr.Expr

arg, args, data, data, funcType, hasFreeVars, indexAccessible, isSimple, markTailCalls, mergeEbv, optimize, typeCheck, uses, visitAll

Methods inherited from class org.basex.query.expr.ExprInfo

toErrorString, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Field Details

VALUE

public static final Empty VALUE

Single instance.

ITER

public static final BasicIter<Item> ITER

Empty iterator.

Method Details

vacuous

public boolean vacuous()

Description copied from class: Expr

Tests if this is a vacuous expression (empty sequence or error function). This check is needed for updating queries.

Overrides:

vacuous in class Expr

Returns:

result of check

size

public long size()

Description copied from class: Expr

Returns the result size, or -1 if the size is unknown.

Overrides:

size in class Item

Returns:

result of check

toJava

public Object toJava()

Description copied from class: Value

Returns a Java representation of the value.

Specified by:

toJava in class Value

Returns:

Java object

iter

public BasicIter<Item> iter()

Description copied from class: Value

Returns an iterator.

Overrides:

iter in class Item

Returns:

iterator

ebv

public Item ebv(QueryContext qc,
 InputInfo ii)

Description copied from class: Expr

Checks if the effective boolean value can be computed for this expression:

• If it yields an empty sequence, Bln.FALSE will be returned.
• If it yields a single item, this item will be returned.
• If it yields nodes, the first node will be returned.
• Otherwise, an error will be raised.

A single numeric item may later be evaluated as positional predicate.

Overrides:

ebv in class Item

Parameters:

qc - query context

ii - input info (required for Seq instances, which have no input info)

Returns:

item

test

public Item test(QueryContext qc,
 InputInfo ii)

Description copied from class: Expr

Performs a predicate test and returns the item if the test was successful. The returned item is required for full-text scoring.

Overrides:

test in class Item

Parameters:

qc - query context

ii - input info (required for Seq instances, which have no input info)

Returns:

item or null

string

public byte[] string(InputInfo ii)

Description copied from class: Item

Returns a string representation of the value.

Specified by:

string in class Item

Parameters:

ii - input info (can be null)

Returns:

string value

eq

public boolean eq(Item item,
 Collation coll,
 StaticContext sc,
 InputInfo ii)

Description copied from class: Item

Compares the items for equality.

Specified by:

eq in class Item

Parameters:

item - item to be compared

coll - collation (can be null)

sc - static context; required for comparing items of type xs:QName (can be null)

ii - input info (can be null)

Returns:

result of check

subsequence

public Empty subsequence(long start,
 long length,
 QueryContext qc)

Description copied from class: Value

Returns a subsequence of this value with the given start and length. The following properties must hold:

• start >= 0,
• length >= 0,
• length <= size() - start

Overrides:

subsequence in class Item

Parameters:

start - starting position

length - number of items

qc - query context

Returns:

sub sequence

seqType

public SeqType seqType()

Description copied from class: Expr

Returns the static type of the resulting value.

Overrides:

seqType in class Item

Returns:

result of check

hash

public int hash(InputInfo ii)

Description copied from class: Value

Returns a hash code for this value.

Overrides:

hash in class Item

Parameters:

ii - input info

Returns:

hash code

atomIter

public Iter atomIter(QueryContext qc,
 InputInfo ii)

Description copied from class: Expr

Evaluates the expression and returns an iterator on the resulting, atomized items.

Overrides:

atomIter in class Expr

Parameters:

qc - query context

ii - input info

Returns:

iterator

atomSize

public long atomSize()

Description copied from class: Item

Computes the number of atomized items. Overwritten by XQArray.

Overrides:

atomSize in class Item

Returns:

atomized item

simplifyFor

public Expr simplifyFor(CompileContext.Simplify mode,
 CompileContext cc)

Description copied from class: Expr

This function is called at compile time for expressions whose operands might be simplified.

Overrides:

simplifyFor in class Expr

Parameters:

mode - mode of simplification

cc - compilation context

Returns:

simplified or original expression

See Also:

• CompileContext.Simplify

equals

public boolean equals(Object obj)

Description copied from class: Expr

This function is e.g. called by:

• If.optimize(CompileContext), Switch.optimize(CompileContext), Typeswitch.optimize(CompileContext), in order to discard identical expressions.
• CmpR.mergeEbv(Expr, boolean, CompileContext) or CmpSR.mergeEbv(Expr, boolean, CompileContext), in order to merge expressions with identical input.
• CmpG.optimize(CompileContext) or CmpV.optimize(CompileContext), in order to pre-evaluate equality tests.
• CmpG.optimize(CompileContext) or Pos.get(Expr, CmpV.OpV, InputInfo, CompileContext), in order to compare the start and end value.
• PathCache, in order to find identical root values at runtime.

Specified by:

equals in class Expr

description

public String description()

Description copied from class: ExprInfo

Returns a string description of the expression. This method is only called by error messages. Contrary to the ExprInfo.toString() method, arguments are not included in the output.

Overrides:

description in class Item

Returns:

result of check

plan

public void plan(QueryPlan plan)

Description copied from class: ExprInfo

Creates a query plan.

Overrides:

plan in class Item

Parameters:

plan - expression plan

plan

public void plan(QueryString qs)

Description copied from class: ExprInfo

Creates a query string.

Specified by:

plan in class ExprInfo

Parameters:

qs - query string builder