org.apache.commons.collections.comparators.ComparatorChain Maven / Gradle / Ivy
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* 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 org.apache.commons.collections.comparators;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
/**
* 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
* @author Morgan Delagrange
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
*/
public class ComparatorChain implements Comparator, Serializable {
/** Serialization version from Collections 2.0. */
private static final long serialVersionUID = -721644942746081630L;
/** The list of comparators in the chain. */
protected List 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(),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 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 sort; true = reverse sort
*/
public ComparatorChain(Comparator comparator, boolean reverse) {
comparatorChain = new ArrayList();
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
* sort order.
*
* @param list List of Comparators
* @see #ComparatorChain(List,BitSet)
*/
public ComparatorChain(List list) {
this(list,new BitSet(list.size()));
}
/**
* 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.
*
* @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 list, BitSet bits) {
comparatorChain = list;
orderingBits = bits;
}
//-----------------------------------------------------------------------
/**
* Add a Comparator to the end of the chain using the
* forward sort order
*
* @param comparator Comparator with the forward sort order
*/
public void addComparator(Comparator comparator) {
addComparator(comparator,false);
}
/**
* Add a Comparator to the end of the chain using the
* given sort order
*
* @param comparator Comparator to add to the end of the chain
* @param reverse false = forward sort order; true = reverse sort order
*/
public void addComparator(Comparator 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 sort order.
*
* @param index index of the Comparator to replace
* @param comparator Comparator to place at the given index
* @exception IndexOutOfBoundsException
* if index < 0 or index >= size()
*/
public void setComparator(int index, Comparator comparator)
throws IndexOutOfBoundsException {
setComparator(index,comparator,false);
}
/**
* Replace the Comparator at the given index in the
* ComparatorChain, using the given sort order
*
* @param index index of the Comparator to replace
* @param comparator Comparator to set
* @param reverse false = forward sort order; true = reverse sort order
*/
public void setComparator(int index, Comparator comparator, boolean reverse) {
checkLocked();
comparatorChain.set(index,comparator);
if (reverse == true) {
orderingBits.set(index);
} else {
orderingBits.clear(index);
}
}
/**
* Change the sort order at the given index in the
* ComparatorChain to a forward sort.
*
* @param index Index of the ComparatorChain
*/
public void setForwardSort(int index) {
checkLocked();
orderingBits.clear(index);
}
/**
* Change the sort order at the given index in the
* ComparatorChain to a reverse sort.
*
* @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
* @exception UnsupportedOperationException
* if the ComparatorChain does not contain at least one
* Comparator
*/
public int compare(Object o1, Object o2) throws UnsupportedOperationException {
if (isLocked == false) {
checkChainIntegrity();
isLocked = true;
}
// iterate over all comparators in the chain
Iterator comparators = comparatorChain.iterator();
for (int comparatorIndex = 0; comparators.hasNext(); ++comparatorIndex) {
Comparator comparator = (Comparator) comparators.next();
int retval = comparator.compare(o1,o2);
if (retval != 0) {
// invert the order if it is a reverse sort
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 true iff that Object is
* is a {@link Comparator} whose ordering is known to be
* equivalent to mine.
*
* This implementation returns true
* iff object.{@link Object#getClass() 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 {@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;
}
}
}