org.apache.xpath.axes

Class WalkerFactory


public class WalkerFactory
extends 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
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.
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. id(), extension function, etc.) step.
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.

Method Summary

static boolean
canCrissCross(int analysis)
static boolean
canSkipSubtrees(int analysis)
static void
diagnoseIterator(String name, int analysis, Compiler compiler)
static int
getAnalysisBitFromAxes(int axis)
Get a corresponding BIT_XXX from an axis.
static 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)

Field Details

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.
Field Value:
234381312

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!!!
Field Value:
255

BITS_RESERVED

public static final int BITS_RESERVED
4 bits are reserved for future use.
Field Value:
3840

BIT_ANCESTOR

public static final int BIT_ANCESTOR
Bit is on if any of the walkers contain an ancestor step.
Field Value:
8192

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.
Field Value:
16384

BIT_ANY_DESCENDANT_FROM_ROOT

public static final int BIT_ANY_DESCENDANT_FROM_ROOT
Found "//foo" pattern
Field Value:
536870912

BIT_ATTRIBUTE

public static final int BIT_ATTRIBUTE
Bit is on if any of the walkers contain an attribute step.
Field Value:
32768

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.
Field Value:
268435456

BIT_CHILD

public static final int BIT_CHILD
Bit is on if any of the walkers contain a child step.
Field Value:
65536

BIT_DESCENDANT

public static final int BIT_DESCENDANT
Bit is on if any of the walkers contain a descendant step.
Field Value:
131072

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.
Field Value:
262144

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.
Field Value:
67108864

BIT_FOLLOWING

public static final int BIT_FOLLOWING
Bit is on if any of the walkers contain a following step.
Field Value:
524288

BIT_FOLLOWING_SIBLING

public static final int BIT_FOLLOWING_SIBLING
Bit is on if any of the walkers contain a following-sibiling step.
Field Value:
1048576

BIT_MATCH_PATTERN

public static final int BIT_MATCH_PATTERN
Bit is on if the expression is a match pattern.
Field Value:
-2147483648

BIT_NAMESPACE

public static final int BIT_NAMESPACE
Bit is on if any of the walkers contain a namespace step.
Field Value:
2097152

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.
Field Value:
1073741824

BIT_PARENT

public static final int BIT_PARENT
Bit is on if any of the walkers contain a parent step.
Field Value:
4194304

BIT_PRECEDING

public static final int BIT_PRECEDING
Bit is on if any of the walkers contain a preceding step.
Field Value:
8388608

BIT_PRECEDING_SIBLING

public static final int BIT_PRECEDING_SIBLING
Bit is on if any of the walkers contain a preceding-sibling step.
Field Value:
16777216

BIT_PREDICATE

public static final int BIT_PREDICATE
Bit is on if the expression contains a top-level predicate.
Field Value:
4096

BIT_ROOT

public static final int BIT_ROOT
Bit is on if any of the walkers contain a root step.
Field Value:
134217728

BIT_SELF

public static final int BIT_SELF
Bit is on if any of the walkers contain a self step.
Field Value:
33554432

Method Details

canCrissCross

public static boolean canCrissCross(int analysis)

canSkipSubtrees

public static boolean canSkipSubtrees(int analysis)

diagnoseIterator

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

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.

getAnalysisString

public static String getAnalysisString(int analysis)

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.

getStepCount

public static int getStepCount(int analysis)

hasPredicate

public static boolean hasPredicate(int analysis)

isAbsolute

public static boolean isAbsolute(int analysis)

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.

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.

isOneStep

public static boolean isOneStep(int analysis)

isSet

public static boolean isSet(int analysis,
                            int bits)

isWild

public static boolean isWild(int analysis)

mightBeProximate

public static boolean mightBeProximate(Compiler compiler,
                                       int opPos,
                                       int stepType)
            throws TransformerException
Tell if the predicates need to have proximity knowledge.

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.

walksAncestors

public static boolean walksAncestors(int analysis)

walksAttributes

public static boolean walksAttributes(int analysis)

walksChildren

public static boolean walksChildren(int analysis)

walksChildrenAndExtraAndSelfOnly

public static boolean walksChildrenAndExtraAndSelfOnly(int analysis)

walksChildrenOnly

public static boolean walksChildrenOnly(int analysis)

walksDescendants

public static boolean walksDescendants(int analysis)

walksDescendantsAndExtraAndSelfOnly

public static boolean walksDescendantsAndExtraAndSelfOnly(int analysis)

walksDownExtraOnly

public static boolean walksDownExtraOnly(int analysis)

walksDownOnly

public static boolean walksDownOnly(int analysis)

walksExtraNodes

public static boolean walksExtraNodes(int analysis)

walksExtraNodesOnly

public static boolean walksExtraNodesOnly(int analysis)

walksFilteredList

public static boolean walksFilteredList(int analysis)

walksFollowingOnlyMaybeAbsolute

public static boolean walksFollowingOnlyMaybeAbsolute(int analysis)

walksInDocOrder

public static boolean walksInDocOrder(int analysis)

walksNamespaces

public static boolean walksNamespaces(int analysis)

walksSelfOnly

public static boolean walksSelfOnly(int analysis)

walksSideways

public static boolean walksSideways(int analysis)

walksSubtree

public static boolean walksSubtree(int analysis)

walksSubtreeOnly

public static boolean walksSubtreeOnly(int analysis)

walksSubtreeOnlyFromRootOrContext

public static boolean walksSubtreeOnlyFromRootOrContext(int analysis)

walksSubtreeOnlyMaybeAbsolute

public static boolean walksSubtreeOnlyMaybeAbsolute(int analysis)

walksUp

public static boolean walksUp(int analysis)

walksUpOnly

public static boolean walksUpOnly(int analysis)

Copyright B) 2004 Apache XML Project. All Rights Reserved.