net.sf.saxon.expr
Class Literal

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.Literal

All Implemented Interfaces:

Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, InstructionInfoProvider

Direct Known Subclasses:

StringLiteral

public class Literal
extends Expression

A Literal is an expression whose value is constant: it is a class that implements the Expression interface as a wrapper around a Value. This may derive from an actual literal in an XPath expression or query, or it may be the result of evaluating a constant subexpression such as true() or xs:date('2007-01-16')

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Literal(Value value)
Create a literal as a wrapper around a Value

Method Summary

int	computeCardinality() Determine the cardinality
int	computeSpecialProperties() Compute the static properties of this expression (other than its type).
void	display(int level, PrintStream out, Configuration config) Diagnostic display of the expression
boolean	effectiveBooleanValue(XPathContext context) Get the effective boolean value of the expression.
boolean	equals(Object obj) Determine whether two literals are equal, when considered as expressions.
String	evaluateAsString(XPathContext context) Evaluate an expression as a String.
Item	evaluateItem(XPathContext context) Evaluate as a singleton item (or empty sequence).
int	getDependencies() Determine which aspects of the context the expression depends on.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items in the expression, if possible
Value	getValue() Get the value represented by this Literal
int	hashCode() Return a hash code to support the equals() function
static boolean	isAtomic(Expression exp) Test whether the literal wraps an atomic value.
static boolean	isConstantBoolean(Expression exp, boolean value) Test if a literal represents the boolean value true
static boolean	isConstantOne(Expression exp) Test if a literal represents the integer value 1
static boolean	isEmptySequence(Expression exp) Test whether the literal explicitly wraps an empty sequence.
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
static Literal	makeLiteral(Value value) Create a literal as a wrapper around a Value
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Optimize an expression
void	process(XPathContext context) Process the value as an instruction, without returning any tail calls
Expression	simplify(StaticContext env) Simplify an expression
Expression	typeCheck(StaticContext env, ItemType contextItemType) TypeCheck an expression

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, getCardinality, getColumnNumber, getContainingProcedure, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterateSubExpressions, markTailFunctionCalls, promote, replaceSubExpression, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Literal

public Literal(Value value)

Create a literal as a wrapper around a Value

Parameters:

value -

Method Detail

makeLiteral

public static Literal makeLiteral(Value value)

Create a literal as a wrapper around a Value

Parameters:

value -

getValue

public Value getValue()

Get the value represented by this Literal

simplify

public final Expression simplify(StaticContext env)

Simplify an expression

Overrides:

simplify in class Expression

Returns:

for a Value, this always returns the value unchanged

typeCheck

public final Expression typeCheck(StaticContext env,
                                  ItemType contextItemType)

TypeCheck an expression

Overrides:

typeCheck in class Expression

Parameters:

env - the static context of the expression

contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE

Returns:

for a Value, this always returns the value unchanged

optimize

public final Expression optimize(Optimizer opt,
                                 StaticContext env,
                                 ItemType contextItemType)

Optimize an expression

Overrides:

optimize in class Expression

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

env - the static context of the expression

contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE

Returns:

for a Value, this always returns the value unchanged

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the items in the expression, if possible

Specified by:

getItemType in class Expression

Parameters:

th - The TypeHierarchy. Can be null if the target is an AtomicValue.

Returns:

for the default implementation: AnyItemType (not known)

computeCardinality

public int computeCardinality()

Determine the cardinality

computeSpecialProperties

public int computeSpecialProperties()

Compute the static properties of this expression (other than its type). For a Value, the only special property is StaticProperty.NON_CREATIVE.

Overrides:

computeSpecialProperties in class Expression

Returns:

StaticProperty.NON_CREATIVE

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

Overrides:

getDependencies in class Expression

Returns:

for a Value, this always returns zero.

iterate

public 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.

Specified by:

iterate in interface SequenceIterable

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

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate as a singleton item (or empty sequence). Note: this implementation returns the first item in the sequence. The method should not be used unless appropriate type-checking has been done to ensure that the value will be a singleton.

Specified by:

evaluateItem in interface EvaluableItem

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

process

public void process(XPathContext context)
             throws XPathException

Process the value as an 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

evaluateAsString

public String evaluateAsString(XPathContext context)
                        throws XPathException

Description copied from class: Expression

Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.

Overrides:

evaluateAsString in class Expression

Parameters:

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

Returns:

the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".

Throws:

XPathException - if any dynamic error occurs evaluating the expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException

Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Overrides:

effectiveBooleanValue in class Expression

Parameters:

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

Returns:

the effective boolean value

Throws:

XPathException - if any dynamic error occurs evaluating the expression

equals

public boolean equals(Object obj)

Determine whether two literals are equal, when considered as expressions.

Overrides:

equals in class Object

Parameters:

obj - the other expression

Returns:

true if the two literals are equal

hashCode

public int hashCode()

Return a hash code to support the equals() function

Overrides:

hashCode in class Object

display

public void display(int level,
                    PrintStream out,
                    Configuration config)

Diagnostic display of the expression

Specified by:

display in class Expression

Parameters:

level - indentation level for this expression

out - Output destination

isAtomic

public static boolean isAtomic(Expression exp)

Test whether the literal wraps an atomic value. (Note, if this method returns false, this still leaves the possibility that the literal wraps a sequence that happens to contain a single atomic value).

Parameters:

exp - an expression

Returns:

if the expression is a literal and the literal wraps an AtomicValue

isEmptySequence

public static boolean isEmptySequence(Expression exp)

Test whether the literal explicitly wraps an empty sequence. (Note, if this method returns false, this still leaves the possibility that the literal wraps a sequence that happens to be empty).

Parameters:

exp - an expression

Returns:

if the expression is a literal and the literal wraps an AtomicValue

isConstantBoolean

public static boolean isConstantBoolean(Expression exp,
                                        boolean value)

Test if a literal represents the boolean value true

Parameters:

exp - an expression

value - true or false

Returns:

if the expression is a literal and the literal represents the boolean value given in the second argument

isConstantOne

public static boolean isConstantOne(Expression exp)

Test if a literal represents the integer value 1

Parameters:

exp - an expression

Returns:

if the expression is a literal and the literal represents the integer value 1