com.feilong.lib.collection4.comparators.ComparatorChain Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of feilong Show documentation
Show all versions of feilong Show documentation
feilong is a suite of core and expanded libraries that include utility classes, http, excel,cvs, io classes, and much much more.
/*
* 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.feilong.lib.collection4.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.
*
*
* @param
* the type of objects compared by this comparator
* @since 2.0
*/
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. */
private final List> comparatorChain;
/** Order - false (clear) = ascend; true (set) = descend. */
private BitSet orderingBits = null;
/** Whether the chain has been "locked". */
private 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(final 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(final Comparator comparator, final boolean reverse){
comparatorChain = new ArrayList<>(1);
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(final 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(final List> list, final 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(final 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(final Comparator comparator,final 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
* @throws IndexOutOfBoundsException
* if index < 0 or index >= size()
*/
public void setComparator(final int index,final 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(final int index,final Comparator comparator,final 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(final 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(final 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;
}
/**
* Throws an exception if the {@link ComparatorChain} is locked.
*
* @throws UnsupportedOperationException
* if the {@link ComparatorChain} is locked
*/
private void checkLocked(){
if (isLocked == true){
throw new UnsupportedOperationException("Comparator ordering cannot be changed after the first comparison is performed");
}
}
/**
* Throws an exception if the {@link ComparatorChain} is empty.
*
* @throws UnsupportedOperationException
* if the {@link ComparatorChain} is empty
*/
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
*/
@Override
public int compare(final E o1,final E o2) throws UnsupportedOperationException{
if (isLocked == false){
checkChainIntegrity();
isLocked = true;
}
// iterate over all comparators in the chain
final Iterator> comparators = comparatorChain.iterator();
for (int comparatorIndex = 0; comparators.hasNext(); ++comparatorIndex){
final 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 (retval > 0){
retval = -1;
}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 3.0
*/
@Override
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 3.0
*/
@Override
public boolean equals(final Object object){
if (this == object){
return true;
}
if (null == object){
return false;
}
if (object.getClass().equals(this.getClass())){
final ComparatorChain chain = (ComparatorChain) object;
return (null == orderingBits ? null == chain.orderingBits : orderingBits.equals(chain.orderingBits))
&& (null == comparatorChain ? null == chain.comparatorChain : comparatorChain.equals(chain.comparatorChain));
}
return false;
}
}