org.apache.commons.collections.comparators
Class ComparatorChain<T>

java.lang.Object
  org.apache.commons.collections.comparators.ComparatorChain<T>

All Implemented Interfaces:

Serializable, Comparator<T>

public class ComparatorChain<T>
extends Object
implements Comparator<T>, Serializable

A ComparatorChain is a Comparator that wraps one or more Comparators in sequence. The ComparatorChain calls each Comparator in sequence until either 1) any single Comparator returns a non-zero result (and that result is then returned), or 2) the ComparatorChain is exhausted (and zero is returned). This type of sorting is very similar to multi-column sorting in SQL, and this class allows Java classes to emulate that kind of behaviour when sorting a List.

To further facilitate SQL-like sorting, the order of any single Comparator in the list can be reversed.

Calling a method that adds new Comparators or changes the ascend/descend sort after compare(Object, Object) has been called will result in an UnsupportedOperationException. However, take care to not alter the underlying List of Comparators or the BitSet that defines the sort order.

Instances of ComparatorChain are not synchronized. The class is not thread-safe at construction time, but it is thread-safe to perform multiple comparisons after all the setup operations are complete.

Since:

Commons Collections 2.0

Version:

$Revision: 1.1.1.1 $ $Date: 2005/05/23 04:34:08 $

Author:

Matt Hall, John Watkinson, Morgan Delagrange

See Also:

Serialized Form

Field Summary

protected List<Comparator<T>>	comparatorChain The list of comparators in the chain.
protected boolean	isLocked Whether the chain has been "locked".
protected BitSet	orderingBits Order - false (clear) = ascend; true (set) = descend.

Constructor Summary

ComparatorChain()
Construct a ComparatorChain with no Comparators.

ComparatorChain(Comparator<T> comparator)
Construct a ComparatorChain with a single Comparator, sorting in the forward order

ComparatorChain(Comparator<T> comparator, boolean reverse)
Construct a Comparator chain with a single Comparator, sorting in the given order

ComparatorChain(List<Comparator<T>> list)
Construct a ComparatorChain from the Comparators in the List.

ComparatorChain(List<Comparator<T>> list, BitSet bits)
Construct a ComparatorChain from the Comparators in the given List.

Method Summary

void	addComparator(Comparator<T> comparator) Add a Comparator to the end of the chain using the forward sort order
void	addComparator(Comparator<T> comparator, boolean reverse) Add a Comparator to the end of the chain using the given sort order
int	compare(T o1, T o2) Perform comparisons on the Objects as per Comparator.compare(o1,o2).
boolean	equals(Object object) Returns true iff that Object is is a Comparator whose ordering is known to be equivalent to mine.
int	hashCode() Implement a hash code for this comparator that is consistent with equals.
boolean	isLocked() Determine if modifications can still be made to the ComparatorChain.
void	setComparator(int index, Comparator<T> comparator) Replace the Comparator at the given index, maintaining the existing sort order.
void	setComparator(int index, Comparator<T> comparator, boolean reverse) Replace the Comparator at the given index in the ComparatorChain, using the given sort order
void	setForwardSort(int index) Change the sort order at the given index in the ComparatorChain to a forward sort.
void	setReverseSort(int index) Change the sort order at the given index in the ComparatorChain to a reverse sort.
int	size() Number of Comparators in the current ComparatorChain.

Methods inherited from class java.lang.Object

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

Field Detail

comparatorChain

protected List<Comparator<T>> comparatorChain

The list of comparators in the chain.

orderingBits

protected BitSet orderingBits

Order - false (clear) = ascend; true (set) = descend.

isLocked

protected boolean isLocked

Whether the chain has been "locked".

Constructor Detail

ComparatorChain

public ComparatorChain()

Construct a ComparatorChain with no Comparators. You must add at least one Comparator before calling the compare(Object,Object) method, or an UnsupportedOperationException is thrown

ComparatorChain

public ComparatorChain(Comparator<T> comparator)

Construct a ComparatorChain with a single Comparator, sorting in the forward order

Parameters:

comparator - First comparator in the Comparator chain

ComparatorChain

public ComparatorChain(Comparator<T> comparator,
                       boolean reverse)

Construct a Comparator chain with a single Comparator, sorting in the given order

Parameters:

comparator - First Comparator in the ComparatorChain

reverse - false = forward sort; true = reverse sort

ComparatorChain

public ComparatorChain(List<Comparator<T>> list)

Construct a ComparatorChain from the Comparators in the List. All Comparators will default to the forward sort order.

Parameters:

list - List of Comparators

See Also:

ComparatorChain(List,BitSet)

ComparatorChain

public ComparatorChain(List<Comparator<T>> list,
                       BitSet bits)

Construct a ComparatorChain from the Comparators in the given List. The sort order of each column will be drawn from the given BitSet. When determining the sort order for Comparator at index i in the List, the ComparatorChain will call BitSet.get(i). If that method returns false, the forward sort order is used; a return value of true indicates reverse sort order.

Parameters:

list - List of Comparators. NOTE: This constructor does not perform a defensive copy of the list

bits - Sort order for each Comparator. Extra bits are ignored, unless extra Comparators are added by another method.

Method Detail

addComparator

public void addComparator(Comparator<T> comparator)

Add a Comparator to the end of the chain using the forward sort order

Parameters:

comparator - Comparator with the forward sort order

addComparator

public void addComparator(Comparator<T> comparator,
                          boolean reverse)

Add a Comparator to the end of the chain using the given sort order

Parameters:

comparator - Comparator to add to the end of the chain

reverse - false = forward sort order; true = reverse sort order

setComparator

public void setComparator(int index,
                          Comparator<T> comparator)
                   throws IndexOutOfBoundsException

Replace the Comparator at the given index, maintaining the existing sort order.

Parameters:

index - index of the Comparator to replace

comparator - Comparator to place at the given index

Throws:

IndexOutOfBoundsException - if index < 0 or index >= size()

setComparator

public void setComparator(int index,
                          Comparator<T> comparator,
                          boolean reverse)

Replace the Comparator at the given index in the ComparatorChain, using the given sort order

Parameters:

index - index of the Comparator to replace

comparator - Comparator to set

reverse - false = forward sort order; true = reverse sort order

setForwardSort

public void setForwardSort(int index)

Change the sort order at the given index in the ComparatorChain to a forward sort.

Parameters:

index - Index of the ComparatorChain

setReverseSort

public void setReverseSort(int index)

Change the sort order at the given index in the ComparatorChain to a reverse sort.

Parameters:

index - Index of the ComparatorChain

size

public int size()

Number of Comparators in the current ComparatorChain.

Returns:

Comparator count

isLocked

public boolean isLocked()

Determine if modifications can still be made to the ComparatorChain. ComparatorChains cannot be modified once they have performed a comparison.

Returns:

true = ComparatorChain cannot be modified; false = ComparatorChain can still be modified.

compare

public int compare(T o1,
                   T o2)
            throws UnsupportedOperationException

Perform comparisons on the Objects as per Comparator.compare(o1,o2).

Specified by:

compare in interface Comparator<T>

Parameters:

o1 - the first object to compare

o2 - the second object to compare

Returns:

-1, 0, or 1

Throws:

UnsupportedOperationException - if the ComparatorChain does not contain at least one Comparator

hashCode

public int hashCode()

Implement a hash code for this comparator that is consistent with equals.

Overrides:

hashCode in class Object

Returns:

a suitable hash code

Since:

Commons Collections 3.0

equals

public boolean equals(Object object)

Returns true iff that Object is is a Comparator whose ordering is known to be equivalent to mine.

This implementation returns true iff object.getClass() equals this.getClass(), and the underlying comparators and order bits are equal. Subclasses may want to override this behavior to remain consistent with the Comparator.equals(Object) contract.

Specified by:

equals in interface Comparator<T>

Overrides:

equals in class Object

Parameters:

object - the object to compare with

Returns:

true if equal

Since:

Commons Collections 3.0