Invertible Comparator
import java.io.Serializable;
import java.util.Comparator;
/*
* Copyright 2002-2005 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* A decorator for a comparator, with an "ascending" flag denoting
* whether comparison results should be treated in forward (standard
* ascending) order or flipped for reverse (descending) order.
*
* @author Keith Donald
* @author Juergen Hoeller
* @since 1.2.2
*/
public class InvertibleComparator implements Comparator, Serializable {
private final Comparator comparator;
private boolean ascending = true;
/**
* Create an InvertibleComparator that sorts ascending by default.
* For the actual comparison, the specified Comparator will be used.
* @param comparator the comparator to decorate
*/
public InvertibleComparator(Comparator comparator) {
this.comparator = comparator;
}
/**
* Create an InvertibleComparator that sorts based on the provided order.
* For the actual comparison, the specified Comparator will be used.
* @param comparator the comparator to decorate
* @param ascending the sort order: ascending (true) or descending (false)
*/
public InvertibleComparator(Comparator comparator, boolean ascending) {
this.comparator = comparator;
setAscending(ascending);
}
/**
* Specify the sort order: ascending (true) or descending (false).
*/
public void setAscending(boolean ascending) {
this.ascending = ascending;
}
/**
* Return the sort order: ascending (true) or descending (false).
*/
public boolean isAscending() {
return ascending;
}
/**
* Invert the sort order: ascending -> descending or
* descending -> ascending.
*/
public void invertOrder() {
this.ascending = !this.ascending;
}
public int compare(Object o1, Object o2) {
int result = this.comparator.compare(o1, o2);
if (result != 0) {
// Invert the order if it is a reverse sort.
if (!this.ascending) {
if (Integer.MIN_VALUE == result) {
result = Integer.MAX_VALUE;
}
else {
result *= -1;
}
}
return result;
}
return 0;
}
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof InvertibleComparator)) {
return false;
}
InvertibleComparator other = (InvertibleComparator) obj;
return (this.comparator.equals(other.comparator) && this.ascending == other.ascending);
}
public int hashCode() {
return this.comparator.hashCode();
}
public String toString() {
return "InvertibleComparator: [" + this.comparator + "]; ascending=" + this.ascending;
}
}
Related examples in the same category
