org.basex.query.expr

Class CmpG

java.lang.Object

org.basex.data.ExprInfo

org.basex.query.expr.Expr

org.basex.query.expr.ParseExpr

org.basex.query.expr.Arr

org.basex.query.expr.Cmp

org.basex.query.expr.CmpG

public final class CmpG
extends Cmp

General comparison.

Author:

BaseX Team 2005-12, BSD License, Christian Gruen

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	CmpG.OpG Comparators.

Nested classes/interfaces inherited from class org.basex.query.expr.Expr

Expr.Use

Field Summary

Fields inherited from class org.basex.query.expr.Arr

expr

Fields inherited from class org.basex.query.expr.ParseExpr

input, size, type

Constructor Summary

Constructors

Constructor and Description
CmpG(InputInfo ii, Expr e1, Expr e2, CmpG.OpG o) Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
Expr	comp(QueryContext ctx) Compiles and optimizes the expression, assigns data types and cardinalities.
Expr	compEbv(QueryContext ctx) This method is called at compile time by expressions that perform effective boolean value tests (e.g.
java.lang.String	description() Returns a string description of the expression.
boolean	indexAccessible(IndexContext ic) Checks if an expression can be rewritten to an index access.
Expr	indexEquivalent(IndexContext ic) Returns an equivalent expression which accesses an index structure.
static AxisStep	indexStep(Expr expr) If possible, returns the last location step of the specified expression.
CmpG	invert() If possible, inverts the operands of the expression.
Bln	item(QueryContext ctx, InputInfo ii) Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence.
void	plan(Serializer ser) Serializes the expression tree.
java.lang.String	toString()

Methods inherited from class org.basex.query.expr.Arr

allAreValues, count, removable, remove, toString, uses

Methods inherited from class org.basex.query.expr.ParseExpr

checkBln, checkColl, checkCreate, checkCtx, checkDbl, checkDBNode, checkEStr, checkEStr, checkIO, checkItem, checkItr, checkItr, checkMap, checkNode, checkNoEmpty, checkStr, checkType, checkUp, checkUp, checkWrite, compBln, ebv, iter, optPre, preEval, size, test, type, value

Methods inherited from class org.basex.query.expr.Expr

addText, hasFreeVars, isEmpty, isFunction, isItem, isVacuous, isValue, iterable, markTailCalls, sameAs

Methods inherited from class org.basex.data.ExprInfo

info

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

CmpG

public CmpG(InputInfo ii,
    Expr e1,
    Expr e2,
    CmpG.OpG o)

Constructor.

Parameters:

ii - input info

e1 - first expression

e2 - second expression

o - operator

Method Detail

comp

public Expr comp(QueryContext ctx)
          throws QueryException

Description copied from class: Expr

Compiles and optimizes the expression, assigns data types and cardinalities.

Overrides:

comp in class Arr

Parameters:

ctx - query context

Returns:

optimized expression

Throws:

QueryException - query exception

compEbv

public Expr compEbv(QueryContext ctx)

Description copied from class: Expr

This method is called at compile time by expressions that perform effective boolean value tests (e.g. If or Preds). If the arguments of the called expression return a boolean anyway, the expression will be simplified.

Example in CmpV: if($x eq true()) is rewritten to if($x), if $x will always yield a single boolean.

Overrides:

compEbv in class Expr

Parameters:

ctx - query context

Returns:

optimized expression

item

public Bln item(QueryContext ctx,
       InputInfo ii)
         throws QueryException

Description copied from class: Expr

Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence. If this method is not overwritten, Expr.iter(org.basex.query.QueryContext) must be implemented by an expression, as it may be called by this method.

Overrides:

item in class ParseExpr

Parameters:

ctx - query context

ii - input info

Returns:

iterator

Throws:

QueryException - query exception

invert

public CmpG invert()

Description copied from class: Cmp

If possible, inverts the operands of the expression.

Specified by:

invert in class Cmp

Returns:

original or modified expression

indexAccessible

public boolean indexAccessible(IndexContext ic)
                        throws QueryException

Description copied from class: Expr

Checks if an expression can be rewritten to an index access. If this method is implemented, Expr.indexEquivalent(org.basex.query.util.IndexContext) must be implemented as well.

Overrides:

indexAccessible in class Expr

Parameters:

ic - index context

Returns:

true if an index can be used

Throws:

QueryException - query exception

indexEquivalent

public Expr indexEquivalent(IndexContext ic)

Description copied from class: Expr

Returns an equivalent expression which accesses an index structure. Will be called if Expr.indexAccessible(org.basex.query.util.IndexContext) is returns true for an expression.

Overrides:

indexEquivalent in class Arr

Parameters:

ic - index context

Returns:

equivalent index-expression

indexStep

public static AxisStep indexStep(Expr expr)

If possible, returns the last location step of the specified expression.

Parameters:

expr - expression

Returns:

location step

plan

public void plan(Serializer ser)
          throws java.io.IOException

Description copied from class: ExprInfo

Serializes the expression tree.

Overrides:

plan in class Arr

Parameters:

ser - serializer

Throws:

java.io.IOException - I/O exception

description

public java.lang.String description()

Description copied from class: ExprInfo

Returns a string description of the expression. This method is only called by error messages. Contrary to the ExprInfo.toString() method, arguments are not included in the output.

Overrides:

description in class ExprInfo

Returns:

result of check

toString

public java.lang.String toString()

Specified by:

toString in class ExprInfo