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[COLLECTIONS-429] Improved CollectionUtils#containsAll with the version from the patch, added more javadoc with information on the runtime/space trade-off. 

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1469039 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Thomas Neidhart 2013-04-17 19:32:34 +00:00
parent 2067c96f3f
commit 6f42ddf1ba
2 changed files with 32 additions and 24 deletions
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6
src/changes/changes.xml
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@ -22,6 +22,12 @@
<body>
<release version="4.0" date="TBA" description="Next release">
<action issue="COLLECTIONS-429,COLLECTION-434" dev="tn" type="add" due-to="Adrian Nistor, Mert Guldur">
Added method "CollectionUtils#containsAll(Collection, Collection)" with guaranteed
runtime complexity of O(n + m) and space complexity of O(n). This method may yield much
better performance than "Collection#containsAll(Collection)" depending on the use-case and
type of collection used.
</action>
<action issue="COLLECTIONS-285" dev="tn" type="add" due-to="Christian Gruenberg">
Added serialization support for "TreeBidiMap".
</action>

50
src/main/java/org/apache/commons/collections4/CollectionUtils.java
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@ -105,23 +105,6 @@ public class CollectionUtils {
return getFreq(obj, cardinalityB);
}
/**
* Returns the number of unique elements in collection A.
* @return the number of unique elements in collection A
*/
@SuppressWarnings("unused")
public int sizeA() {
return cardinalityA.size();
}
/**
* Returns the number of unique elements in collection A.
* @return the number of unique elements in collection A
*/
public int sizeB() {
return cardinalityB.size();
}
private final int getFreq(final Object obj, final Map<?, Integer> freqMap) {
final Integer count = freqMap.get(obj);
if (count != null) {
@ -366,9 +349,10 @@ public class CollectionUtils {
* will be returned.
* <p>
* This method is intended as a replacement for {@link Collection#containsAll(Collection)}
* with a guaranteed runtime complexity of {@code O(n)}. Depending on the type of
* with a guaranteed runtime complexity of {@code O(n + m)}. Depending on the type of
* {@link Collection} provided, this method will be much faster than calling
* {@link Collection#containsAll(Collection)} instead.
* {@link Collection#containsAll(Collection)} instead, though this will come at the
* cost of an additional space complexity O(n).
*
* @param coll1 the first collection, must not be null
* @param coll2 the second collection, must not be null
@ -380,12 +364,30 @@ public class CollectionUtils {
if (coll2.isEmpty()) {
return true;
} else {
final SetOperationCardinalityHelper<Object> helper =
new SetOperationCardinalityHelper<Object>(coll1, coll2);
for (final Object obj : helper) {
helper.setCardinality(obj, helper.min(obj));
final Iterator<?> it = coll1.iterator();
final Set<Object> elementsAlreadySeen = new HashSet<Object>();
for (final Object nextElement : coll2) {
if (elementsAlreadySeen.contains(nextElement)) {
continue;
}
boolean foundCurrentElement = false;
while (it.hasNext()) {
final Object p = it.next();
elementsAlreadySeen.add(p);
if (nextElement == null ? p == null : nextElement.equals(p)) {
foundCurrentElement = true;
break;
}
}
if (foundCurrentElement) {
continue;
} else {
return false;
}
}
return helper.list().size() == helper.sizeB();
return true;
}
}