org.basex.query.item

Class Value

java.lang.Object

org.basex.data.ExprInfo

org.basex.query.expr.Expr

org.basex.query.item.Value

All Implemented Interfaces:

java.lang.Iterable<Item>

Direct Known Subclasses:

Empty, Item, Seq

public abstract class Value
extends Expr
implements java.lang.Iterable<Item>

Abstract value. This class also implements the Iterable interface, which is why all of its values can also be retrieved via enhanced for (for-each) loops. Note, however, that using the default iter() method will give you better performance.

Author:

BaseX Team 2005-12, BSD License, Christian Gruen

Nested Class Summary

Nested classes/interfaces inherited from class org.basex.query.expr.Expr

Expr.Use

Field Summary

Fields

Modifier and Type	Field and Description
Type	type Data type.

Method Summary

Methods

Modifier and Type	Method and Description
ItemCache	cache() Creates an ItemCache, containing all items of this value.
Value	comp(QueryContext ctx) Compiles and optimizes the expression, assigns data types and cardinalities.
int	count(Var v) Counts how often the specified variable is used by an expression.
Data	data() Returns the data reference (if) attached to this value.
java.lang.String	description() Returns a string description of the expression.
abstract int	hash(InputInfo ii) Returns a hash code for this value.
abstract boolean	homogenous() Checks if all items of this value share the same type.
java.lang.String	info() Returns the simplified class name.
boolean	isValue() Tests if this is a value.
abstract Item	itemAt(long pos) Gets the item at the given position in the value.
abstract ValueIter	iter() Returns an iterator.
ValueIter	iter(QueryContext ctx) Evaluates the expression and returns an iterator on the resulting items.
java.util.Iterator<Item>	iterator()
boolean	removable(Var v) Checks if the specified variable is replaceable by a context item.
Expr	remove(Var v) Substitutes all VarRef expressions for the given variable by a Context reference.
abstract long	size() Returns the sequence size or 1.
abstract java.lang.Object	toJava() Returns a Java representation of the value.
boolean	uses(Expr.Use u) Indicates if an expression uses the specified type or operation.
Value	value(QueryContext ctx) Evaluates the expression and returns the resulting value.
abstract int	writeTo(Item[] arr, int start) Writes this value's items out to the given array.

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

addText, compEbv, ebv, hasFreeVars, indexAccessible, indexEquivalent, isEmpty, isFunction, isItem, isVacuous, item, iterable, markTailCalls, sameAs, test, type

Methods inherited from class org.basex.data.ExprInfo

plan, toString

Methods inherited from class java.lang.Object

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

Field Detail

type

public Type type

Data type.

Method Detail

comp

public final Value comp(QueryContext ctx)

Description copied from class: Expr

Compiles and optimizes the expression, assigns data types and cardinalities.

Specified by:

comp in class Expr

Parameters:

ctx - query context

Returns:

optimized expression

iter

public final ValueIter iter(QueryContext ctx)

Description copied from class: Expr

Evaluates the expression and returns an iterator on the resulting items. If this method is not overwritten, Expr.item(org.basex.query.QueryContext, org.basex.util.InputInfo) must be implemented by an expression, as it may be called by this method.

Specified by:

iter in class Expr

Parameters:

ctx - query context

Returns:

resulting item

iterator

public final java.util.Iterator<Item> iterator()

Specified by:

iterator in interface java.lang.Iterable<Item>

iter

public abstract ValueIter iter()

Returns an iterator.

Returns:

iterator

value

public final Value value(QueryContext ctx)

Description copied from class: Expr

Evaluates the expression and returns the resulting value.

Specified by:

value in class Expr

Parameters:

ctx - query context

Returns:

iterator

data

public Data data()

Returns the data reference (if) attached to this value.

Returns:

data reference

isValue

public final boolean isValue()

Description copied from class: Expr

Tests if this is a value.

Overrides:

isValue in class Expr

Returns:

result of check

size

public abstract long size()

Description copied from class: Expr

Returns the sequence size or 1.

Specified by:

size in class Expr

Returns:

result of check

toJava

public abstract java.lang.Object toJava()
                                 throws QueryException

Returns a Java representation of the value.

Returns:

Java object

Throws:

QueryException - query exception

uses

public boolean uses(Expr.Use u)

Description copied from class: Expr

Indicates if an expression uses the specified type or operation. This method is called by numerous Expr.comp(org.basex.query.QueryContext) methods to test the properties of sub-expressions. It will return true as soon as at least one test is successful.

Specified by:

uses in class Expr

Parameters:

u - type/operation to be found

Returns:

result of check

count

public int count(Var v)

Description copied from class: Expr

Counts how often the specified variable is used by an expression. This method is called by:

• GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates and remove statically bound or unused clauses
• GFLWOR.compHoist(org.basex.query.QueryContext) to hoist independent variables

Specified by:

count in class Expr

Parameters:

v - variable to be checked

Returns:

number of occurrences

removable

public final boolean removable(Var v)

Description copied from class: Expr

Checks if the specified variable is replaceable by a context item. The following tests might return false:

• Preds.removable(org.basex.query.util.Var), if one of the variables is used within a predicate.
• MixedPath.removable(org.basex.query.util.Var), if the variable occurs within the path.
• Group.removable(org.basex.query.util.Var), as the group by expression depends on variable references.

This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses into predicates.

Specified by:

removable in class Expr

Parameters:

v - variable to be replaced

Returns:

result of check

remove

public final Expr remove(Var v)

Description copied from class: Expr

Substitutes all VarRef expressions for the given variable by a Context reference. This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates.

Specified by:

remove in class Expr

Parameters:

v - variable to be replaced

Returns:

new expression

description

public java.lang.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 ExprInfo

Returns:

result of check

info

public final java.lang.String info()

Description copied from class: ExprInfo

Returns the simplified class name.

Overrides:

info in class ExprInfo

Returns:

class name

hash

public abstract int hash(InputInfo ii)
                  throws QueryException

Returns a hash code for this value.

Parameters:

ii - input info

Returns:

hash code

Throws:

QueryException - if atomization can't be applied (e.g. function item)

writeTo

public abstract int writeTo(Item[] arr,
          int start)

Writes this value's items out to the given array.

Parameters:

arr - array to write to

start - start position

Returns:

number of written items

cache

public final ItemCache cache()

Creates an ItemCache, containing all items of this value. Use with care, as compressed Values are expanded, creating many objects.

Returns:

cached items

itemAt

public abstract Item itemAt(long pos)

Gets the item at the given position in the value.

Parameters:

pos - position

Returns:

item

homogenous

public abstract boolean homogenous()

Checks if all items of this value share the same type.

Returns:

result of check