com.icl.saxon.expr

Class Expression

Known Direct 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

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.
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 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(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.

Field Details

staticContext

protected StaticContext staticContext

Method Details

containsReferences

public boolean containsReferences()
            throws XPathException
Determine whether the expression contains any references to variables
Returns:
true if so

display

public abstract void display(int level)
Diagnostic print of expression structure

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.

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

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.

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 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

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)

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

getStaticContext

public final StaticContext getStaticContext()
Determine the static context used when the expression was parsed

indent

protected static String indent(int level)
Construct indent string, for diagnostic output

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.

make

public static Expression make(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

outputStringValue

public void outputStringValue(Outputter out,
                              Context context)
            throws 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

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

setStaticContext

public final void setStaticContext(StaticContext sc)
Set the static context used when the expression was parsed

simplify

public Expression simplify()
            throws XPathException
Simplify an expression. Default implementation does nothing.
Returns:
the simplified expression

usesCurrent

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