org.codehaus.plexus.util.CollectionUtils Maven / Gradle / Ivy
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package org.codehaus.plexus.util;
/*
* Copyright The Codehaus Foundation.
*
* 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.
*/
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @author olamy
* @version $Id$
*/
public class CollectionUtils
{
// ----------------------------------------------------------------------
// Static methods that can probably be moved to a real util class.
// ----------------------------------------------------------------------
/**
* Take a dominant and recessive Map and merge the key:value pairs where the recessive Map may add key:value pairs
* to the dominant Map but may not override any existing key:value pairs. If we have two Maps, a dominant and
* recessive, and their respective keys are as follows: dominantMapKeys = { a, b, c, d, e, f } recessiveMapKeys = {
* a, b, c, x, y, z } Then the result should be the following: resultantKeys = { a, b, c, d, e, f, x, y, z }
*
* @param dominantMap Dominant Map.
* @param recessiveMap Recessive Map.
* @return The result map with combined dominant and recessive values.
*/
public static Map mergeMaps( Map dominantMap, Map recessiveMap )
{
if ( dominantMap == null && recessiveMap == null )
{
return null;
}
if ( dominantMap != null && recessiveMap == null )
{
return dominantMap;
}
if ( dominantMap == null )
{
return recessiveMap;
}
Map result = new HashMap();
// Grab the keys from the dominant and recessive maps.
Set dominantMapKeys = dominantMap.keySet();
Set recessiveMapKeys = recessiveMap.keySet();
// Create the set of keys that will be contributed by the
// recessive Map by subtracting the intersection of keys
// from the recessive Map's keys.
Collection contributingRecessiveKeys =
CollectionUtils.subtract( recessiveMapKeys,
CollectionUtils.intersection( dominantMapKeys, recessiveMapKeys ) );
result.putAll( dominantMap );
// Now take the keys we just found and extract the values from
// the recessiveMap and put the key:value pairs into the dominantMap.
for ( K key : contributingRecessiveKeys )
{
result.put( key, recessiveMap.get( key ) );
}
return result;
}
/**
* Take a series of Maps and merge them where the ordering of the array from 0..n is the dominant
* order.
*
* @param maps An array of Maps to merge.
* @return Map The result Map produced after the merging process.
*/
public static Map mergeMaps( Map[] maps )
{
Map result;
if ( maps.length == 0 )
{
result = null;
}
else if ( maps.length == 1 )
{
result = maps[0];
}
else
{
result = mergeMaps( maps[0], maps[1] );
for ( int i = 2; i < maps.length; i++ )
{
result = mergeMaps( result, maps[i] );
}
}
return result;
}
/**
* Returns a {@link Collection} containing the intersection of the given {@link Collection}s.
*
* The cardinality of each element in the returned {@link Collection} will be equal to the minimum of the
* cardinality of that element in the two given {@link Collection}s.
*
* @param a The first collection
* @param b The second collection
* @see Collection#retainAll
* @return The intersection of a and b, never null
*/
public static Collection intersection( final Collection a, final Collection b )
{
ArrayList list = new ArrayList();
Map mapa = getCardinalityMap( a );
Map mapb = getCardinalityMap( b );
Set elts = new HashSet( a );
elts.addAll( b );
for ( E obj : elts )
{
for ( int i = 0, m = Math.min( getFreq( obj, mapa ), getFreq( obj, mapb ) ); i < m; i++ )
{
list.add( obj );
}
}
return list;
}
/**
* Returns a {@link Collection} containing a - b. The cardinality of each element e in
* the returned {@link Collection} will be the cardinality of e in a minus the cardinality of e
* in b, or zero, whichever is greater.
*
* @param a The start collection
* @param b The collection that will be subtracted
* @see Collection#removeAll
* @return The result of the subtraction
*/
public static Collection subtract( final Collection a, final Collection b )
{
ArrayList list = new ArrayList( a );
for ( T aB : b )
{
list.remove( aB );
}
return list;
}
/**
* Returns a {@link Map} mapping each unique element in the given {@link Collection} to an {@link Integer}
* representing the number of occurrences of that element in the {@link Collection}. An entry that maps to
* null indicates that the element does not appear in the given {@link Collection}.
*
* @param col The collection to count cardinalities for
* @return A map of counts, indexed on each element in the collection
*/
public static Map getCardinalityMap( final Collection col )
{
HashMap count = new HashMap();
for ( E obj : col )
{
Integer c = count.get( obj );
if ( null == c )
{
count.put( obj, 1 );
}
else
{
count.put( obj, c + 1 );
}
}
return count;
}
public static List iteratorToList( Iterator it )
{
if ( it == null )
{
throw new NullPointerException( "it cannot be null." );
}
List list = new ArrayList();
while ( it.hasNext() )
{
list.add( it.next() );
}
return list;
}
// ----------------------------------------------------------------------
//
// ----------------------------------------------------------------------
private static int getFreq( final E obj, final Map freqMap )
{
try
{
Integer o = freqMap.get( obj );
if ( o != null ) // minimize NullPointerExceptions
{
return o;
}
}
catch ( NullPointerException ignore )
{
}
catch ( NoSuchElementException ignore )
{
}
return 0;
}
}