net.sf.saxon.value
Class Value

java.lang.Object
  net.sf.saxon.value.Value

All Implemented Interfaces:

Serializable, Expression

Direct Known Subclasses:

AtomicValue, SequenceValue, SingletonNode

public abstract class Value
extends Object
implements Expression, Serializable

A value is the result of an expression but it is also an expression in its own right. Note that every value can be regarded as a sequence - in many cases, a sequence of length one.

See Also:

Serialized Form

Constructor Summary

Value()

Method Summary

Expression	analyze(StaticContext env) TypeCheck an expression
static Item	asItem(Value value, XPathContext context) Static method to make an Item from a Value
static Value	asValue(Item item) Static method to make a Value from a given Item (which may be either an AtomicValue or a NodeInfo
static CharSequence	collapseWhitespace(CharSequence in) Collapse whitespace as defined in XML Schema
abstract int	conversionPreference(Class required) Get conversion preference for this value to a Java class.
abstract Object	convertToJava(Class target) Convert to Java object (for passing to external functions)
int	getDependencies() Determine which aspects of the context the expression depends on.
int	getSpecialProperties() Get the static properties of this expression (other than its type).
Expression[]	getSubExpressions() Get the sub-expressions of this expression.
static int	inverse(int operator) Return the inverse of a relational operator, so that "a op b" can be rewritten as "b inverse(op) a"
static CharSequence	normalizeWhitespace(CharSequence in) Normalize whitespace as defined in XML Schema
Expression	promote(PromotionOffer offer) Offer promotion for this subexpression.
Expression	simplify() Simplify an expression
static long	stringToInteger(CharSequence s) Static method to convert strings to integers.
static double	stringToNumber(CharSequence s) Static method to convert strings to numbers.
static CharSequence	trimWhitespace(CharSequence in) Remove leading and trailing whitespace.

Methods inherited from class java.lang.Object

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

Methods inherited from interface net.sf.saxon.expr.Expression

display, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getItemType, iterate

Constructor Detail

Value

public Value()

Method Detail

asValue

public static Value asValue(Item item)

Static method to make a Value from a given Item (which may be either an AtomicValue or a NodeInfo

Parameters:

item - The supplied item, or null, indicating the empty sequence.

Returns:

The supplied item, if it is a value, or a SingletonNode that wraps the item, if it is a node. If the supplied value was null, return an EmptySequence

asItem

public static Item asItem(Value value,
                          XPathContext context)
                   throws XPathException

Static method to make an Item from a Value

Parameters:

value - the value to be converted

context - the context. It is probably safe to set this to null.

Returns:

null if the value is an empty sequence; or the only item in the value if it is a singleton sequence

Throws:

XPathException - if the Value contains multiple items

stringToNumber

public static double stringToNumber(CharSequence s)
                             throws NumberFormatException

Static method to convert strings to numbers. Might as well go here as anywhere else.

Parameters:

s - the String to be converted

Returns:

a double representing the value of the String

Throws:

NumberFormatException - if the value cannot be converted

stringToInteger

public static long stringToInteger(CharSequence s)
                            throws XPathException

Static method to convert strings to integers.

Parameters:

s - the String to be converted

Returns:

a long representing the value of the String; if it cannot be converted, throw an exception

Throws:

XPathException

normalizeWhitespace

public static CharSequence normalizeWhitespace(CharSequence in)

Normalize whitespace as defined in XML Schema

collapseWhitespace

public static CharSequence collapseWhitespace(CharSequence in)

Collapse whitespace as defined in XML Schema

trimWhitespace

public static CharSequence trimWhitespace(CharSequence in)

Remove leading and trailing whitespace. This has the same effect as collapseWhitespace, but is cheaper, for use by data types that do not allow internal whitespace.

Parameters:

in - the input string whose whitespace is to be removed

Returns:

the result of removing excess whitespace

simplify

public final Expression simplify()

Simplify an expression

Specified by:

simplify in interface Expression

Returns:

the simplified expression

analyze

public final Expression analyze(StaticContext env)

TypeCheck an expression

Specified by:

analyze in interface Expression

Parameters:

env - the static context of the expression

Returns:

the simplified expression

getSubExpressions

public final Expression[] getSubExpressions()

Get the sub-expressions of this expression. Always returns an empty array

Specified by:

getSubExpressions in interface Expression

Returns:

an array containing the sub-expressions of this expression

getSpecialProperties

public int getSpecialProperties()

Description copied from interface: Expression

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Specified by:

getSpecialProperties in interface Expression

Returns:

a set of flags indicating static properties of this expression

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Offer promotion for this subexpression. Values (constant expressions) are never promoted

Specified by:

promote in interface Expression

Parameters:

offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression

Returns:

if promotion is not possible, returns the expression unchanged. If promotion has occurred, returns the expression suitably modified.

Throws:

XPathException - if any error is detected

getDependencies

public final int getDependencies()

Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.VARIABLES and StaticProperty.CURRENT_NODE

Specified by:

getDependencies in interface Expression

Returns:

a set of bit-significant flags identifying the dependencies of the expression

inverse

public static final int inverse(int operator)

Return the inverse of a relational operator, so that "a op b" can be rewritten as "b inverse(op) a"

convertToJava

public abstract Object convertToJava(Class target)
                              throws XPathException

Convert to Java object (for passing to external functions)

Parameters:

target - The class required by the external function

Returns:

an object of the target class

Throws:

XPathException

conversionPreference

public abstract int conversionPreference(Class required)

Get conversion preference for this value to a Java class. A low result indicates higher preference.