: Class Expression

com.icl.saxon.expr
Class Expression

java.lang.Object

  |

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

Direct Known Subclasses:

AttributeValueTemplate, ErrorExpression, Function, IsLastExpression, NodeSetComparison, NodeSetExpression, SingletonComparison, Value, VariableReference

public abstract class Expression

extends java.lang.Object

This class serves two purposes: it is an abstract superclass for different kinds of XPath expression, and it contains a static method to invoke the expression parser

Field Summary

protected StaticContext

staticContext

Constructor Summary

Expression()

Method Summary

boolean	containsReferences() Determine whether the expression contains any references to variables
abstract void	display(int level) Diagnostic print of expression structure
NodeEnumeration	enumerate(Context context, boolean sorted) Return an enumeration of nodes in a nodeset.
abstract Value	evaluate(Context context) Evaluate an expression.
boolean	evaluateAsBoolean(Context context) Evaluate an expression as a Boolean. The result of x.evaluateAsBoolean(c) must be equivalent to x.evaluate(c).asBoolean(); but optimisations are possible when it is known that a boolean result is required, especially in the case of a NodeSet.
NodeSetValue	evaluateAsNodeSet(Context context) Evaluate an expression as a NodeSet.
double	evaluateAsNumber(Context context) Evaluate an expression as a Number. The result of x.evaluateAsNumber(c) must be equivalent to x.evaluate(c).asNumber(); but optimisations are possible when it is known that a numeric result is required, especially in the case of a NodeSet.
java.lang.String	evaluateAsString(Context context) Evaluate an expression as a String. The result of x.evaluateAsString(c) must be equivalent to x.evaluate(c).asString(); but optimisations are possible when it is known that a string result is required, especially in the case of a NodeSet.
abstract int	getDataType() Determine the data type of the expression, if possible
abstract int	getDependencies() Determine which aspects of the context the expression depends on.
StaticContext	getStaticContext() Determine the static context used when the expression was parsed
protected static java.lang.String	indent(int level) Construct indent string, for diagnostic output
boolean	isContextDocumentNodeSet() Determine, in the case of an expression whose data type is Value.NODESET, whether all the nodes in the node-set are guaranteed to come from the same document as the context node.
static Expression	make(java.lang.String expression, StaticContext env) Parse an expression
void	outputStringValue(Outputter out, Context context) Evaluate an expression as a String and write the result to the specified outputter.
abstract Expression	reduce(int dependencies, Context context) Perform a partial evaluation of the expression, by eliminating specified dependencies on the context.
void	setStaticContext(StaticContext sc) Set the static context used when the expression was parsed
Expression	simplify() Simplify an expression.
boolean	usesCurrent() Determine whether the expression uses the current() function.

Methods inherited from class java.lang.Object

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

Field Detail

staticContext

protected StaticContext staticContext

Constructor Detail

Expression

public Expression()

Method Detail

make

public static Expression make(java.lang.String expression,
                              StaticContext env)
                       throws XPathException

Parse an expression

Parameters:

expression - The expression (as a character string)

env - An object giving information about the compile-time context of the expression

Returns:

an object of type Expression

simplify

public Expression simplify()
                    throws XPathException

Simplify an expression. Default implementation does nothing.

Returns:

the simplified expression

setStaticContext

public final void setStaticContext(StaticContext sc)

Set the static context used when the expression was parsed

getStaticContext

public final StaticContext getStaticContext()

Determine the static context used when the expression was parsed

containsReferences

public boolean containsReferences()
                           throws XPathException

Determine whether the expression contains any references to variables

Returns:

true if so

evaluate

public abstract Value evaluate(Context context)
                        throws XPathException

Evaluate an expression.

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the value of the expression, evaluated in the current context

evaluateAsBoolean

public boolean evaluateAsBoolean(Context context)
                          throws XPathException

Evaluate an expression as a Boolean.
The result of x.evaluateAsBoolean(c) must be equivalent to x.evaluate(c).asBoolean(); but optimisations are possible when it is known that a boolean result is required, especially in the case of a NodeSet.

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the value of the expression, evaluated in the current context

evaluateAsNumber

public double evaluateAsNumber(Context context)
                        throws XPathException

Evaluate an expression as a Number.
The result of x.evaluateAsNumber(c) must be equivalent to x.evaluate(c).asNumber(); but optimisations are possible when it is known that a numeric result is required, especially in the case of a NodeSet.

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the value of the expression, evaluated in the current context

evaluateAsString

public java.lang.String evaluateAsString(Context context)
                                  throws XPathException

Evaluate an expression as a String.
The result of x.evaluateAsString(c) must be equivalent to x.evaluate(c).asString(); but optimisations are possible when it is known that a string result is required, especially in the case of a NodeSet.

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the value of the expression, evaluated in the current context

outputStringValue

public void outputStringValue(Outputter out,
                              Context context)
                       throws javax.xml.transform.TransformerException

Evaluate an expression as a String and write the result to the specified outputter.

Parameters:

out - The required outputter

context - The context in which the expression is to be evaluated

evaluateAsNodeSet

public NodeSetValue evaluateAsNodeSet(Context context)
                               throws XPathException

Evaluate an expression as a NodeSet.

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the value of the expression, evaluated in the current context. Note that the result is not necessarily in document order; to get it into document order, call sort() on the result.

Throws:

XPathException - when the expression does not return a nodeset.

enumerate

public NodeEnumeration enumerate(Context context,
                                 boolean sorted)
                          throws XPathException

Return an enumeration of nodes in a nodeset.

Parameters:

context - The context in which the expression is to be evaluated

sorted - Indicates whether the nodes are required in document order. If this is false, they may come in any order, but there will be no duplicates.

Throws:

XPathException - when the expression does not return a nodeset.

getDataType

public abstract int getDataType()

Determine the data type of the expression, if possible

Returns:

one of the values Value.STRING, Value.BOOLEAN, Value.NUMBER, Value.NODESET, Value.FRAGMENT, or Value.ANY (meaning not known in advance)

isContextDocumentNodeSet

public boolean isContextDocumentNodeSet()

Determine, in the case of an expression whose data type is Value.NODESET, whether all the nodes in the node-set are guaranteed to come from the same document as the context node. Used for optimization.

usesCurrent

public boolean usesCurrent()

Determine whether the expression uses the current() function. This is an error if the expression is within a pattern

getDependencies

public abstract 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

reduce

public abstract Expression reduce(int dependencies,
                                  Context context)
                           throws XPathException

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

Parameters:

dependencies - The dependencies to be removed, e.g. Context.VARIABLES

context - The context to be used for the partial evaluation

Returns:

a new expression (or Value) that does not have any of the specified dependencies

display

public abstract void display(int level)

Diagnostic print of expression structure

indent

protected static java.lang.String indent(int level)

Construct indent string, for diagnostic output