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Applying Thomas Rogan's patch to COLLECTIONS-328, improving the performance to ListUtils.intersection in the manner described by Jilles van Gurp 

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@965176 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Henri Yandell 2010-07-18 08:07:36 +00:00
parent a11dc6aa1d
commit da5a378c4f
1 changed files with 13 additions and 4 deletions
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17
src/java/org/apache/commons/collections/ListUtils.java
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@ -19,6 +19,7 @@ package org.apache.commons.collections;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
@ -70,12 +71,20 @@ public class ListUtils {
*/
public static <E> List<E> intersection(final List<? extends E> list1, final List<? extends E> list2) {
final List<E> result = new ArrayList<E>();
final ArrayList<E> copyOfList1 = new ArrayList<E>(list1);
for (E e : list2) {
if (copyOfList1.contains(e)) {
List<? extends E> smaller = list1;
List<? extends E> larger = list2;
if (list1.size() > list2.size()) {
smaller = list2;
larger = list1;
}
HashSet<E> hashSet = new HashSet<E>(smaller);
for (E e : larger) {
if (hashSet.contains(e)) {
result.add(e);
copyOfList1.remove(e);
hashSet.remove(e);
}
}
return result;