org.apache.xpath.axes
Class WalkerFactory

java.lang.Object
  |
  +--org.apache.xpath.axes.WalkerFactory

public class WalkerFactory

extends java.lang.Object

This class is both a factory for XPath location path expressions, which are built from the opcode map output, and an analysis engine for the location path expressions in order to provide optimization hints.

Field Summary

static int	BIT_ANCESTOR Bit is on if any of the walkers contain an ancestor step.
static int	BIT_ANCESTOR_OR_SELF Bit is on if any of the walkers contain an ancestor-or-self step.
static int	BIT_ANY_DESCENDANT_FROM_ROOT Found "//foo" pattern
static int	BIT_ATTRIBUTE Bit is on if any of the walkers contain an attribute step.
static int	BIT_BACKWARDS_SELF Bit is on if any of the walkers can go backwards in document order from the context node.
static int	BIT_CHILD Bit is on if any of the walkers contain a child step.
static int	BIT_DESCENDANT Bit is on if any of the walkers contain a descendant step.
static int	BIT_DESCENDANT_OR_SELF Bit is on if any of the walkers contain a descendant-or-self step.
static int	BIT_FILTER Bit is on if any of the walkers contain a filter (i.e.
static int	BIT_FOLLOWING Bit is on if any of the walkers contain a following step.
static int	BIT_FOLLOWING_SIBLING Bit is on if any of the walkers contain a following-sibiling step.
static int	BIT_MATCH_PATTERN Bit is on if the expression is a match pattern.
static int	BIT_NAMESPACE Bit is on if any of the walkers contain a namespace step.
static int	BIT_NODETEST_ANY Bit is on if any of the walkers contain an node() test.
static int	BIT_PARENT Bit is on if any of the walkers contain a parent step.
static int	BIT_PRECEDING Bit is on if any of the walkers contain a preceding step.
static int	BIT_PRECEDING_SIBLING Bit is on if any of the walkers contain a preceding-sibling step.
static int	BIT_PREDICATE Bit is on if the expression contains a top-level predicate.
static int	BIT_ROOT Bit is on if any of the walkers contain a root step.
static int	BIT_SELF Bit is on if any of the walkers contain a self step.
static int	BITMASK_TRAVERSES_OUTSIDE_SUBTREE If any of these bits are on, the expression may likely traverse outside the given subtree.
static int	BITS_COUNT First 8 bits are the number of top-level location steps.
static int	BITS_RESERVED 4 bits are reserved for future use.

Constructor Summary

WalkerFactory()

Method Summary

static boolean	canCrissCross(int analysis)
static boolean	canSkipSubtrees(int analysis)
static void	diagnoseIterator(java.lang.String name, int analysis, Compiler compiler)
static int	getAnalysisBitFromAxes(int axis) Get a corresponding BIT_XXX from an axis.
static java.lang.String	getAnalysisString(int analysis)
static int	getAxisFromStep(Compiler compiler, int stepOpCodePos) Special purpose function to see if we can optimize the pattern for a DescendantIterator.
static int	getStepCount(int analysis)
static boolean	hasPredicate(int analysis)
static boolean	isAbsolute(int analysis)
static boolean	isDownwardAxisOfMany(int axis) Tell if the given axis goes downword.
static boolean	isNaturalDocOrder(int analysis) Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.
static boolean	isOneStep(int analysis)
static boolean	isSet(int analysis, int bits)
static boolean	isWild(int analysis)
static boolean	mightBeProximate(Compiler compiler, int opPos, int stepType) Tell if the predicates need to have proximity knowledge.
static DTMIterator	newDTMIterator(Compiler compiler, int opPos, boolean isTopLevel) Create a new LocPathIterator iterator.
static boolean	walksAncestors(int analysis)
static boolean	walksAttributes(int analysis)
static boolean	walksChildren(int analysis)
static boolean	walksChildrenAndExtraAndSelfOnly(int analysis)
static boolean	walksChildrenOnly(int analysis)
static boolean	walksDescendants(int analysis)
static boolean	walksDescendantsAndExtraAndSelfOnly(int analysis)
static boolean	walksDownExtraOnly(int analysis)
static boolean	walksDownOnly(int analysis)
static boolean	walksExtraNodes(int analysis)
static boolean	walksExtraNodesOnly(int analysis)
static boolean	walksFilteredList(int analysis)
static boolean	walksFollowingOnlyMaybeAbsolute(int analysis)
static boolean	walksInDocOrder(int analysis)
static boolean	walksNamespaces(int analysis)
static boolean	walksSelfOnly(int analysis)
static boolean	walksSideways(int analysis)
static boolean	walksSubtree(int analysis)
static boolean	walksSubtreeOnly(int analysis)
static boolean	walksSubtreeOnlyFromRootOrContext(int analysis)
static boolean	walksSubtreeOnlyMaybeAbsolute(int analysis)
static boolean	walksUp(int analysis)
static boolean	walksUpOnly(int analysis)

Methods inherited from class java.lang.Object

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

Field Detail

BITS_COUNT

public static final int BITS_COUNT

First 8 bits are the number of top-level location steps. Hopefully there will never be more that 255 location steps!!!

BITS_RESERVED

public static final int BITS_RESERVED

4 bits are reserved for future use.

BIT_PREDICATE

public static final int BIT_PREDICATE

Bit is on if the expression contains a top-level predicate.

BIT_ANCESTOR

public static final int BIT_ANCESTOR

Bit is on if any of the walkers contain an ancestor step.

BIT_ANCESTOR_OR_SELF

public static final int BIT_ANCESTOR_OR_SELF

Bit is on if any of the walkers contain an ancestor-or-self step.

BIT_ATTRIBUTE

public static final int BIT_ATTRIBUTE

Bit is on if any of the walkers contain an attribute step.

BIT_CHILD

public static final int BIT_CHILD

Bit is on if any of the walkers contain a child step.

BIT_DESCENDANT

public static final int BIT_DESCENDANT

Bit is on if any of the walkers contain a descendant step.

BIT_DESCENDANT_OR_SELF

public static final int BIT_DESCENDANT_OR_SELF

Bit is on if any of the walkers contain a descendant-or-self step.

BIT_FOLLOWING

public static final int BIT_FOLLOWING

Bit is on if any of the walkers contain a following step.

BIT_FOLLOWING_SIBLING

public static final int BIT_FOLLOWING_SIBLING

Bit is on if any of the walkers contain a following-sibiling step.

BIT_NAMESPACE

public static final int BIT_NAMESPACE

Bit is on if any of the walkers contain a namespace step.

BIT_PARENT

public static final int BIT_PARENT

Bit is on if any of the walkers contain a parent step.

BIT_PRECEDING

public static final int BIT_PRECEDING

Bit is on if any of the walkers contain a preceding step.

BIT_PRECEDING_SIBLING

public static final int BIT_PRECEDING_SIBLING

Bit is on if any of the walkers contain a preceding-sibling step.

BIT_SELF

public static final int BIT_SELF

Bit is on if any of the walkers contain a self step.

BIT_FILTER

public static final int BIT_FILTER

Bit is on if any of the walkers contain a filter (i.e. id(), extension function, etc.) step.

BIT_ROOT

public static final int BIT_ROOT

Bit is on if any of the walkers contain a root step.

BITMASK_TRAVERSES_OUTSIDE_SUBTREE

public static final int BITMASK_TRAVERSES_OUTSIDE_SUBTREE

If any of these bits are on, the expression may likely traverse outside the given subtree.

BIT_BACKWARDS_SELF

public static final int BIT_BACKWARDS_SELF

Bit is on if any of the walkers can go backwards in document order from the context node.

BIT_ANY_DESCENDANT_FROM_ROOT

public static final int BIT_ANY_DESCENDANT_FROM_ROOT

Found "//foo" pattern

BIT_NODETEST_ANY

public static final int BIT_NODETEST_ANY

Bit is on if any of the walkers contain an node() test. This is really only useful if the count is 1.

BIT_MATCH_PATTERN

public static final int BIT_MATCH_PATTERN

Bit is on if the expression is a match pattern.

Constructor Detail

WalkerFactory

public WalkerFactory()

Method Detail

isSet

public static boolean isSet(int analysis,
                            int bits)

diagnoseIterator

public static void diagnoseIterator(java.lang.String name,
                                    int analysis,
                                    Compiler compiler)

newDTMIterator

public static DTMIterator newDTMIterator(Compiler compiler,
                                         int opPos,
                                         boolean isTopLevel)
                                  throws TransformerException

Create a new LocPathIterator iterator. The exact type of iterator returned is based on an analysis of the XPath operations.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

opPos - The position of the operation code for this itterator.

Returns:

non-null reference to a LocPathIterator or derivative.

Throws:

TransformerException -

getAxisFromStep

public static int getAxisFromStep(Compiler compiler,
                                  int stepOpCodePos)
                           throws TransformerException

Special purpose function to see if we can optimize the pattern for a DescendantIterator.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

stepOpCodePos - The opcode position for the step.

Returns:

32 bits as an integer that give information about the location path as a whole.

Throws:

TransformerException -

getAnalysisBitFromAxes

public static int getAnalysisBitFromAxes(int axis)

Get a corresponding BIT_XXX from an axis.

Parameters:

axis - One of Axis.ANCESTOR, etc.

Returns:

One of BIT_ANCESTOR, etc.

mightBeProximate

public static boolean mightBeProximate(Compiler compiler,
                                       int opPos,
                                       int stepType)
                                throws TransformerException

Tell if the predicates need to have proximity knowledge.

isDownwardAxisOfMany

public static boolean isDownwardAxisOfMany(int axis)

Tell if the given axis goes downword. Bogus name, if you can think of a better one, please do tell. This really has to do with inverting attribute axis.

Parameters:

axis - One of Axis.XXX.

Returns:

true if the axis is not a child axis and does not go up from the axis root.

getAnalysisString

public static java.lang.String getAnalysisString(int analysis)

hasPredicate

public static boolean hasPredicate(int analysis)

isWild

public static boolean isWild(int analysis)

walksAncestors

public static boolean walksAncestors(int analysis)

walksAttributes

public static boolean walksAttributes(int analysis)

walksNamespaces

public static boolean walksNamespaces(int analysis)

walksChildren

public static boolean walksChildren(int analysis)

walksDescendants

public static boolean walksDescendants(int analysis)

walksSubtree

public static boolean walksSubtree(int analysis)

walksSubtreeOnlyMaybeAbsolute

public static boolean walksSubtreeOnlyMaybeAbsolute(int analysis)

walksSubtreeOnly

public static boolean walksSubtreeOnly(int analysis)

walksFilteredList

public static boolean walksFilteredList(int analysis)

walksSubtreeOnlyFromRootOrContext

public static boolean walksSubtreeOnlyFromRootOrContext(int analysis)

walksInDocOrder

public static boolean walksInDocOrder(int analysis)

walksFollowingOnlyMaybeAbsolute

public static boolean walksFollowingOnlyMaybeAbsolute(int analysis)

walksUp

public static boolean walksUp(int analysis)

walksSideways

public static boolean walksSideways(int analysis)

walksExtraNodes

public static boolean walksExtraNodes(int analysis)

walksExtraNodesOnly

public static boolean walksExtraNodesOnly(int analysis)

isAbsolute

public static boolean isAbsolute(int analysis)

walksChildrenOnly

public static boolean walksChildrenOnly(int analysis)

walksChildrenAndExtraAndSelfOnly

public static boolean walksChildrenAndExtraAndSelfOnly(int analysis)

walksDescendantsAndExtraAndSelfOnly

public static boolean walksDescendantsAndExtraAndSelfOnly(int analysis)

walksSelfOnly

public static boolean walksSelfOnly(int analysis)

walksUpOnly

public static boolean walksUpOnly(int analysis)

walksDownOnly

public static boolean walksDownOnly(int analysis)

walksDownExtraOnly

public static boolean walksDownExtraOnly(int analysis)

canSkipSubtrees

public static boolean canSkipSubtrees(int analysis)

canCrissCross

public static boolean canCrissCross(int analysis)

isNaturalDocOrder

public static boolean isNaturalDocOrder(int analysis)

Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.

Parameters:

analysis - The general analysis of the pattern.

Returns:

true if the walk can be done in natural order.

Throws:

TransformerException -

isOneStep

public static boolean isOneStep(int analysis)

getStepCount

public static int getStepCount(int analysis)