net.sf.saxon.expr

Class SimpleExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.SimpleExpression

All Implemented Interfaces:

Callable, ExportAgent, Locatable, IdentityComparable

Direct Known Subclasses:

SQLConnect.ConnectInstruction

public abstract class SimpleExpression
extends Expression
implements Callable

An abstract implementation of Expression designed to make it easy to implement new expressions, in particular, expressions to support extension instructions.

An implementation of this class must supply the Callable.call(XPathContext, net.sf.saxon.om.Sequence[]) method to evaluate the expression and return its result.

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
SimpleExpression() Constructor

Method Summary

Modifier and Type	Method and Description
int	computeCardinality() Determine the static cardinality of the expression.
Expression	copy(RebindingMap rebindings) Copy an expression.
protected SimpleExpression	copyOperandsFrom(SimpleExpression se1) Helper method for subclasses to implement the copy() operation: this method can be applied to the new expression to copy operands from the old expressions
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	export(ExpressionPresenter destination) Diagnostic print of expression structure.
java.lang.String	getExpressionType() Return a distinguishing name for the expression, for use in diagnostics.
ItemType	getItemType() Determine the data type of the items returned by this expression.
protected OperandArray	getOperanda() Get the data structure holding the operands of this expression.
SequenceIterator<?>	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
java.lang.Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
void	process(XPathContext context) Process the instruction, without returning any tail calls
void	setArguments(Expression[] sub) Set the immediate sub-expressions of this expression.
protected void	setOperanda(OperandArray operanda) Set the data structure for the operands of this expression.

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

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeHashCode, computeSpecialProperties, computeStaticProperties, dynamicError, effectiveBooleanValue, equals, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getDependencies, getEvaluationMethod, getExpressionName, getExtraProperty, getImplementationMethod, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getStreamerName, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operandSparseList, optimize, optimizeChildren, prepareForStreaming, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, toShortString, toString, typeCheck, typeCheckChildren, typeError, unordered, verifyParentPointers

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

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

call

Constructor Detail

SimpleExpression

public SimpleExpression()

Constructor

Method Detail

setOperanda

protected void setOperanda(OperandArray operanda)

Set the data structure for the operands of this expression. This must be created during initialisation of the expression and must not be subsequently changed

Parameters:

operanda - the data structure for expression operands

getOperanda

protected OperandArray getOperanda()

Get the data structure holding the operands of this expression.

Returns:

the data structure holding expression operands

operands

public java.lang.Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Overrides:

operands in class Expression

Returns:

an iterator containing the sub-expressions of this expression

setArguments

public void setArguments(Expression[] sub)

Set the immediate sub-expressions of this expression.

Parameters:

sub - an array containing the sub-expressions of this expression

copy

public Expression copy(RebindingMap rebindings)

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings - variables that need to be re-bound

Returns:

the copy of the original expression

copyOperandsFrom

protected SimpleExpression copyOperandsFrom(SimpleExpression se1)

Helper method for subclasses to implement the copy() operation: this method can be applied to the new expression to copy operands from the old expressions

Parameters:

se1 - the expression being copied

Returns:

the target object of this method (for convenience)

getItemType

public ItemType getItemType()

Determine the data type of the items returned by this expression. This implementation returns "item()", which can be overridden in a subclass.

Specified by:

getItemType in class Expression

Returns:

the data type

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression. This implementation returns "zero or more", which can be overridden in a subclass.

Specified by:

computeCardinality in class Expression

Returns:

the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE. May also return StaticProperty.ALLOWS_ZERO if the result is known to be an empty sequence, or StaticProperty.ALLOWS_MANY if if is known to return a sequence of length two or more.

evaluateItem

public final Item evaluateItem(XPathContext context)
                        throws XPathException

Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

Overrides:

evaluateItem in class Expression

Parameters:

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

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

iterate

public final SequenceIterator<?> iterate(XPathContext context)
                                  throws XPathException

Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Overrides:

iterate in class Expression

Parameters:

context - supplies the context for evaluation

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

Throws:

XPathException - if any dynamic error occurs evaluating the expression

process

public final void process(XPathContext context)
                   throws XPathException

Process the instruction, without returning any tail calls

Overrides:

process in class Expression

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException - if a dynamic error occurs

export

public void export(ExpressionPresenter destination)
            throws XPathException

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in interface ExportAgent

Specified by:

export in class Expression

Parameters:

destination - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

getExpressionType

public java.lang.String getExpressionType()

Return a distinguishing name for the expression, for use in diagnostics. By default the class name is used.

Returns:

a distinguishing name for the expression (defaults to the name of the implementation class)