/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package com.stratio.cassandra.contrib;
import java.io.Serializable;
import java.util.*;
/**
* <p> 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. </p> <p/> <p> To further facilitate SQL-like sorting, the order of any single Comparator in the list can be
* reversed. </p> <p/> <p> Calling a method that adds new Comparators or changes the ascend/descend sortFields <i>after
* compare(Object, Object) has been called</i> will result in an UnsupportedOperationException. However, <i>take
* care</i> to not alter the underlying List of Comparators or the BitSet that defines the sortFields order. </p> <p/>
* <p> Instances of ComparatorChain are not synchronized. The class is not thread-safe at construction time, but it
* <i>is</i> thread-safe to perform multiple comparisons after all the setup operations are complete. </p>
*
* @author Morgan Delagrange
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
* @since Commons Collections 2.0
*/
public class ComparatorChain<T> implements Comparator<T>, Serializable {
/**
* Serialization version from Collections 2.0.
*/
private static final long serialVersionUID = -721644942746081630L;
/**
* The list of comparators in the chain.
*/
protected List<Comparator<T>> comparatorChain = null;
/**
* Order - false (clear) = ascend; true (set) = descend.
*/
protected BitSet orderingBits = null;
/**
* Whether the chain has been "locked".
*/
protected boolean isLocked = false;
// -----------------------------------------------------------------------
/**
* 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
*/
public ComparatorChain() {
this(new ArrayList<Comparator<T>>(), new BitSet());
}
/**
* Construct a ComparatorChain with a single Comparator, sorting in the forward order
*
* @param comparator First comparator in the Comparator chain
*/
public ComparatorChain(Comparator<T> comparator) {
this(comparator, false);
}
/**
* Construct a Comparator chain with a single Comparator, sorting in the given order
*
* @param comparator First Comparator in the ComparatorChain
* @param reverse false = forward sortFields; true = reverse sortFields
*/
public ComparatorChain(Comparator<T> comparator, boolean reverse) {
comparatorChain = new ArrayList<Comparator<T>>();
comparatorChain.add(comparator);
orderingBits = new BitSet(1);
if (reverse == true) {
orderingBits.set(0);
}
}
/**
* Construct a ComparatorChain from the Comparators in the List. All Comparators will default to the forward
* sortFields order.
*
* @param list List of Comparators
* @see #ComparatorChain(List, BitSet)
*/
public ComparatorChain(List<Comparator<T>> list) {
this(list, new BitSet(list.size()));
}
/**
* Construct a ComparatorChain from the Comparators in the given List. The sortFields order of each column will be
* drawn from the given BitSet. When determining the sortFields order for Comparator at index <i>i</i> in the List,
* the ComparatorChain will call BitSet.get(<i>i</i>). If that method returns <i>false</i>, the forward sortFields
* order is used; a return value of <i>true</i> indicates reverse sortFields order.
*
* @param list List of Comparators. NOTE: This constructor does not perform a defensive copy of the list
* @param bits Sort order for each Comparator. Extra bits are ignored, unless extra Comparators are added by another
* method.
*/
public ComparatorChain(List<Comparator<T>> list, BitSet bits) {
comparatorChain = list;
orderingBits = bits;
}
// -----------------------------------------------------------------------
/**
* Add a Comparator to the end of the chain using the forward sortFields order
*
* @param comparator Comparator with the forward sortFields order
*/
public void addComparator(Comparator<T> comparator) {
addComparator(comparator, false);
}
/**
* Add a Comparator to the end of the chain using the given sortFields order
*
* @param comparator Comparator to add to the end of the chain
* @param reverse false = forward sortFields order; true = reverse sortFields order
*/
public void addComparator(Comparator<T> comparator, boolean reverse) {
checkLocked();
comparatorChain.add(comparator);
if (reverse == true) {
orderingBits.set(comparatorChain.size() - 1);
}
}
/**
* Replace the Comparator at the given index, maintaining the existing sortFields order.
*
* @param index index of the Comparator to replace
* @param comparator Comparator to place at the given index
* @throws IndexOutOfBoundsException if index < 0 or index >= size()
*/
public void setComparator(int index, Comparator<T> comparator) throws IndexOutOfBoundsException {
setComparator(index, comparator, false);
}
/**
* Replace the Comparator at the given index in the ComparatorChain, using the given sortFields order
*
* @param index index of the Comparator to replace
* @param comparator Comparator to set
* @param reverse false = forward sortFields order; true = reverse sortFields order
*/
public void setComparator(int index, Comparator<T> comparator, boolean reverse) {
checkLocked();
comparatorChain.set(index, comparator);
if (reverse == true) {
orderingBits.set(index);
} else {
orderingBits.clear(index);
}
}
/**
* Change the sortFields order at the given index in the ComparatorChain to a forward sortFields.
*
* @param index Index of the ComparatorChain
*/
public void setForwardSort(int index) {
checkLocked();
orderingBits.clear(index);
}
/**
* Change the sortFields order at the given index in the ComparatorChain to a reverse sortFields.
*
* @param index Index of the ComparatorChain
*/
public void setReverseSort(int index) {
checkLocked();
orderingBits.set(index);
}
/**
* Number of Comparators in the current ComparatorChain.
*
* @return Comparator count
*/
public int size() {
return comparatorChain.size();
}
/**
* Determine if modifications can still be made to the ComparatorChain. ComparatorChains cannot be modified once
* they have performed a comparison.
*
* @return true = ComparatorChain cannot be modified; false = ComparatorChain can still be modified.
*/
public boolean isLocked() {
return isLocked;
}
// throw an exception if the ComparatorChain is locked
private void checkLocked() {
if (isLocked == true) {
throw new UnsupportedOperationException(
"Comparator ordering cannot be changed after the first comparison is performed");
}
}
private void checkChainIntegrity() {
if (comparatorChain.size() == 0) {
throw new UnsupportedOperationException("ComparatorChains must contain at least one Comparator");
}
}
// -----------------------------------------------------------------------
/**
* Perform comparisons on the Objects as per Comparator.compare(o1,o2).
*
* @param o1 the first object to compare
* @param o2 the second object to compare
* @return -1, 0, or 1
* @throws UnsupportedOperationException if the ComparatorChain does not contain at least one Comparator
*/
public int compare(T o1, T o2) throws UnsupportedOperationException {
if (isLocked == false) {
checkChainIntegrity();
isLocked = true;
}
// iterate over all comparators in the chain
Iterator<Comparator<T>> comparators = comparatorChain.iterator();
for (int comparatorIndex = 0; comparators.hasNext(); ++comparatorIndex) {
Comparator<T> comparator = comparators.next();
int retval = comparator.compare(o1, o2);
if (retval != 0) {
// invert the order if it is a reverse sortFields
if (orderingBits.get(comparatorIndex) == true) {
if (Integer.MIN_VALUE == retval) {
retval = Integer.MAX_VALUE;
} else {
retval *= -1;
}
}
return retval;
}
}
// if comparators are exhausted, return 0
return 0;
}
// -----------------------------------------------------------------------
/**
* Implement a hash code for this comparator that is consistent with {@link #equals(Object) equals}.
*
* @return a suitable hash code
* @since Commons Collections 3.0
*/
public int hashCode() {
int hash = 0;
if (null != comparatorChain) {
hash ^= comparatorChain.hashCode();
}
if (null != orderingBits) {
hash ^= orderingBits.hashCode();
}
return hash;
}
/**
* Returns <code>true</code> iff <i>that</i> Object is is a {@link Comparator} whose ordering is known to be
* equivalent to mine.
* <p/>
* This implementation returns <code>true</code> iff <code><i>object</i>.{@link Object#getClass() getClass()}</code>
* equals <code>this.getClass()</code>, and the underlying comparators and order bits are equal. Subclasses may want
* to override this behavior to remain consistent with the {@link Comparator#equals(Object)} contract.
*
* @param object the object to compare with
* @return true if equal
* @since Commons Collections 3.0
*/
public boolean equals(Object object) {
if (this == object) {
return true;
} else if (null == object) {
return false;
} else if (object.getClass().equals(this.getClass())) {
ComparatorChain<?> chain = (ComparatorChain<?>) object;
return ((null == orderingBits ? null == chain.orderingBits : orderingBits.equals(chain.orderingBits)) &&
(null == comparatorChain ?
null == chain.comparatorChain :
comparatorChain.equals(chain.comparatorChain)));
} else {
return false;
}
}
}