com.bigdata.bop.ap.filter

Class SameVariableConstraint<E>

java.lang.Object

com.bigdata.bop.ap.filter.SameVariableConstraint<E>

Type Parameters:

E - The generic type of the elements that will be tested by the filter.

All Implemented Interfaces:

IFilterTest, Externalizable, Serializable

public class SameVariableConstraint<E>
extends Object
implements IFilterTest, Externalizable

Filter imposes the "same variable" constraint on the elements visited by an IAccessPath. The filter is required IFF a IVariable appears in more than one position for the IPredicate associated with the IAccessPath. For example, in spo(?g, p1, o1, ?g), the variable g shows up at both index ZERO (0) and index THREE (3).

An instance of the filter is created by passing in an IPredicate. The filter creates an array of variables which appear more than once and the index at which those variables appear in the predicate. The filter then does the minimum amount of work and just compares the values found in the different slots in which each variable appears for only those variables which appear more than once in the IPredicate.

Version:

$Id$

Author:

Bryan Thompson

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected int[]	indices An array containing one or more records, each of which has the form

Constructor Summary

Constructors

Constructor and Description
SameVariableConstraint() De-serialization constructor.
SameVariableConstraint(IPredicate<E> p, int[] indices)

Method Summary

Methods

Modifier and Type	Method and Description
int[]	getIndices()
boolean	isValid(Object obj) True iff the argument is matched by the filter.
static <E> SameVariableConstraint<E>	newInstance(IPredicate<E> p) The filter is only created and populated for variables which appear more than once in the predicate.
void	readExternal(ObjectInput in)
String	toString()
void	writeExternal(ObjectOutput out)

Methods inherited from class java.lang.Object

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

Field Detail

indices

protected int[] indices

An array containing one or more records, each of which has the form

 [n,index[0], index[1], ... index[n-1]]
 

, where n is the number of occurrences of some variable and index[i], for i in [0,n-1], gives each index in the predicate at which that variable appears.

For example, given the predicate

 spo(?g,p1,o1,?g)
 

the array would be coded as one record

 [2, 0, 3]
 

Given the predicate

 foo(?g,?h,?h,?g,4,?h)
 

the array would be coded as two records

 [[2, 0, 3], [3, 1, 2, 5]]
 

where the records are indicated by the nested square brackets.

Constructor Detail

SameVariableConstraint

public SameVariableConstraint()

De-serialization constructor.

SameVariableConstraint

public SameVariableConstraint(IPredicate<E> p,
                      int[] indices)

Method Detail

isValid

public boolean isValid(Object obj)

Description copied from interface: IFilterTest

True iff the argument is matched by the filter.

Specified by:

isValid in interface IFilterTest

Returns:

true iff that object is accepted by the filter.

getIndices

public int[] getIndices()

toString

public String toString()

Overrides:

toString in class Object

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Throws:

IOException

ClassNotFoundException

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

Specified by:

writeExternal in interface Externalizable

Throws:

IOException

newInstance

public static <E> SameVariableConstraint<E> newInstance(IPredicate<E> p)

The filter is only created and populated for variables which appear more than once in the predicate. If there are no variables which appear more than once, then the filter IS NOT created.

Type Parameters:

E - The generic type of the elements to be tested by the filter.

Parameters:

p - The predicate.

Returns:

The filter -or- null iff no variables appear more than once in the IPredicate.