: Class Value

com.icl.saxon.expr
Class Value

java.lang.Object

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  +--com.icl.saxon.expr.Expression

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        +--com.icl.saxon.expr.Value

Direct Known Subclasses:

BooleanValue, NodeSetValue, NumericValue, ObjectValue, StringValue

public abstract class Value

extends Expression

A value is the result of an expression but it is also an expression in its own right

Field Summary

static int	ANY
static int	BOOLEAN Constants denoting the data types of an expression or value
static int	NODESET
static int	NUMBER
static int	OBJECT
static int	STRING

Fields inherited from class com.icl.saxon.expr.Expression

staticContext

Constructor Summary

Value()

Method Summary

abstract boolean	asBoolean() Convert the value to a Boolean
abstract double	asNumber() Convert the value to a Number
abstract java.lang.String	asString() Convert the value to a String value
boolean	compare(int operator, Value other) Test how a Value compares to another Value under a relational comparison.
abstract int	conversionPreference(java.lang.Class required) Get conversion preference for this value to a Java class.
abstract java.lang.Object	convertToJava(java.lang.Class target) Convert to Java object (for passing to external functions)
boolean	equals(Value other) Test whether two values are equal.
Value	evaluate(Context context) Evaluate the Value.
int	getDependencies() Determine which aspects of the context the expression depends on.
protected 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"
boolean	notEquals(Value other) Test whether two values are not-equal.
protected boolean	numericCompare(int operator, double x, double y)
Expression	reduce(int dependencies, Context context) Perform a partial evaluation of the expression, by eliminating specified dependencies on the context.
Expression	simplify() Simplify an expression
static double	stringToNumber(java.lang.String s) Static method to convert strings to numbers.

Methods inherited from class com.icl.saxon.expr.Expression

containsReferences, display, enumerate, evaluateAsBoolean, evaluateAsNodeSet, evaluateAsNumber, evaluateAsString, getDataType, getStaticContext, indent, isContextDocumentNodeSet, make, outputStringValue, setStaticContext, usesCurrent

Methods inherited from class java.lang.Object

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

Field Detail

BOOLEAN

public static final int BOOLEAN

Constants denoting the data types of an expression or value

NUMBER

public static final int NUMBER

STRING

public static final int STRING

NODESET

public static final int NODESET

OBJECT

public static final int OBJECT

ANY

public static final int ANY

Constructor Detail

Value

public Value()

Method Detail

stringToNumber

public static double stringToNumber(java.lang.String s)

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; if it cannot be converted, return NaN (as required by the XSL specification)

evaluate

public Value evaluate(Context context)
               throws XPathException

Evaluate the Value. Null operation, because it has already been evaluated

Overrides:

evaluate in class Expression

Parameters:

context - The context (not used)

Returns:

the value, unchanged

simplify

public Expression simplify()

Simplify an expression

Overrides:

simplify in class Expression

Returns:

the simplified expression

getDependencies

public 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 Context.VARIABLES and Context.CURRENT_NODE

Overrides:

getDependencies in class Expression

asString

public abstract java.lang.String asString()
                                   throws XPathException

Convert the value to a String value

Returns:

the value converted to a String

asNumber

public abstract double asNumber()
                         throws XPathException

Convert the value to a Number

Returns:

the value converted to a String

asBoolean

public abstract boolean asBoolean()
                           throws XPathException

Convert the value to a Boolean

Returns:

the value converted to a Boolean

equals

public boolean equals(Value other)
               throws XPathException

Test whether two values are equal. See the XSL specification: if either operand is a nodeset, they are compared as nodesets; else if either is a boolean, they are compared as booleans; else if either operand is a number, they are compared as numbers; else they are compared as strings.

Returns:

a boolean giving the value of the expression, evaluated in the current context

notEquals

public boolean notEquals(Value other)
                  throws XPathException

Test whether two values are not-equal. Note that a!=b means the same as !(a=b) except where either a or b is a nodeset.

Returns:

a boolean giving the value of the expression, evaluated in the current context

compare

public boolean compare(int operator,
                       Value other)
                throws XPathException

Test how a Value compares to another Value under a relational comparison. Note that the method is overridden for NodeSetValue

Parameters:

operator - The comparison operator, one of Tokenizer.LE, Tokenizer.LT, Tokenizer.GE, Tokenizer.GT, Tokenizer.EQUALS, Tokenizer.NE.

inverse

protected 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"

numericCompare

protected final boolean numericCompare(int operator,
                                       double x,
                                       double y)

reduce

public Expression reduce(int dependencies,
                         Context context)

Perform a partial evaluation of the expression, by eliminating specified dependencies on the context.

Overrides:

reduce in class Expression

Parameters:

dependencies - The dependencies to be removed

context - The context to be used for the partial evaluation

Returns:

a new expression that does not have any of the specified dependencies

convertToJava

public abstract java.lang.Object convertToJava(java.lang.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

conversionPreference

public abstract int conversionPreference(java.lang.Class required)

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