blackboard.base
Class BaseComparator

java.lang.Object
  blackboard.base.BaseComparator

All Implemented Interfaces:

java.util.Comparator

Direct Known Subclasses:

GenericFieldComparator

public abstract class BaseComparator
extends java.lang.Object
implements java.util.Comparator

Base comparator class that implements ascending/descending and chaining. Comparators may be chained together in a linked list to support a succession of orderings.

Since:

Bb 6.0

Version:

$Revision: #1 $ $Date: 2005/06/27 $

Field Summary

static boolean	ASCENDING ASCENDING constant for use in this class's constructor.
static boolean	DESCENDING DESCENDING constant for use in this class's constructor.

Constructor Summary

protected

BaseComparator(boolean ascending) Constructor.

Method Summary

void	appendSecondaryComparator(java.util.Comparator comparator) Appends the provided Comparator to the end of this linked list of comparators.
int	compare(java.lang.Object o1, java.lang.Object o2) Applies the lined list of comparators to resolve the objects relationship.
static BaseComparator	convertToBaseComparator(java.util.Comparator comparator) Wraps any comparator in an instance of BaseComparator that proxies through to the supplied comparator.
protected abstract int	doCompare(java.lang.Object o1, java.lang.Object o2) Subclasses must override this method to provide functionality.
boolean	isAscending() Returns true if this comparator has been set to compare objects in ascending order.
void	setAscending(boolean ascending) Sets this comparators ascending/descending mode.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Comparator

equals

Field Detail

ASCENDING

public static final boolean ASCENDING

ASCENDING constant for use in this class's constructor.

See Also:

Constant Field Values

DESCENDING

public static final boolean DESCENDING

DESCENDING constant for use in this class's constructor.

See Also:

Constant Field Values

Constructor Detail

BaseComparator

protected BaseComparator(boolean ascending)

Constructor.

Parameters:

ascending - Provides a generic way to reverse the ordering without having to implement an additional comparator class. An object's natural ordering is by definition ascending.

Method Detail

isAscending

public final boolean isAscending()

Returns true if this comparator has been set to compare objects in ascending order. This fields allows an ordering to be reversed without modifying the underlying comparator.

setAscending

public final void setAscending(boolean ascending)

Sets this comparators ascending/descending mode. To reverse the order that a list is sorted using a comparator, one could do:

 comparator.setAscending( !comparator.isAscending() );
 

appendSecondaryComparator

public final void appendSecondaryComparator(java.util.Comparator comparator)

Appends the provided Comparator to the end of this linked list of comparators. The comparator does not have to be a subclass of BaseComparator.

compare

public final int compare(java.lang.Object o1,
                         java.lang.Object o2)
                  throws java.lang.ClassCastException,
                         java.lang.IllegalArgumentException

Applies the lined list of comparators to resolve the objects relationship. The comparators in the list are applied in order. Each time a comparator finds the objects to be equal based on its criteria, the next comparator in the list is called. This allows for arbitrarily nested 'order by' functionality.

Specified by:

compare in interface java.util.Comparator

Throws:

java.lang.ClassCastException

java.lang.IllegalArgumentException

doCompare

protected abstract int doCompare(java.lang.Object o1,
                                 java.lang.Object o2)
                          throws java.lang.ClassCastException,
                                 java.lang.IllegalArgumentException

Subclasses must override this method to provide functionality. This method follows the same rules as the methods java.util.Comparator.compare( Object, Object ). Implementations should return the value according to this comparator's ordering rules without taking into account ascending / descending.

Throws:

java.lang.ClassCastException

java.lang.IllegalArgumentException

convertToBaseComparator

public static BaseComparator convertToBaseComparator(java.util.Comparator comparator)

Wraps any comparator in an instance of BaseComparator that proxies through to the supplied comparator. The new BaseComparator instance is initialized in ASCENDING mode. If the provided comparator is already and instance of BaseComparator, then it is returned unmodified.