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[COLLECTIONS-412] Improved performance of CollectionUtils#subtract. Thanks to Adrian Nistor for report and patch. 

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1353111 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Thomas Neidhart 2012-06-23 11:31:54 +00:00
parent 13c8e44e6a
commit cae889f3c0
1 changed files with 18 additions and 4 deletions
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22
src/main/java/org/apache/commons/collections/CollectionUtils.java
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@ -28,6 +28,7 @@ import java.util.ListIterator;
import java.util.Map;
import java.util.Set;
import org.apache.commons.collections.bag.HashBag;
import org.apache.commons.collections.collection.PredicatedCollection;
import org.apache.commons.collections.collection.SynchronizedCollection;
import org.apache.commons.collections.collection.TransformedCollection;
@ -246,6 +247,12 @@ public class CollectionUtils {
* <i>b</i>. Only the elements of <i>b</i> that satisfy the predicate
* condition, <i>p</i> are subtracted from <i>a</i>.
*
* <p>The cardinality of each element <i>e</i> in the returned {@link Collection}
* that satisfies the predicate condition will be the cardinality of <i>e</i> in <i>a</i>
* minus the cardinality of <i>e</i> in <i>b</i>, or zero, whichever is greater.</p>
* <p>The cardinality of each element <i>e</i> in the returned {@link Collection} that does <b>not</b>
* satisfy the predicate condition will be equal to the cardinality of <i>e</i> in <i>a</i>.</p>
*
* @param a the collection to subtract from, must not be null
* @param b the collection to subtract, must not be null
* @param p the condition used to determine which elements of <i>b</i> are
@ -256,12 +263,19 @@ public class CollectionUtils {
* @since 4.0
* @see Collection#removeAll
*/
public static <O> Collection<O> subtract(final Iterable<? extends O> a, final Iterable<? extends O> b, final Predicate<O> p) {
ArrayList<O> list = new ArrayList<O>();
addAll(list, a);
public static <O> Collection<O> subtract(final Iterable<? extends O> a,
final Iterable<? extends O> b,
final Predicate<O> p) {
final ArrayList<O> list = new ArrayList<O>();
final HashBag<O> bag = new HashBag<O>();
for (O element : b) {
if (p.evaluate(element)) {
list.remove(element);
bag.add(element);
}
}
for (O element : a) {
if (!bag.remove(element, 1)) {
list.add(element);
}
}
return list;