[COLLECTIONS-556] Added method SetUtils.identityHashSet.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1681635 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Thomas Neidhart 2015-05-25 19:18:50 +00:00
parent 0e11402b98
commit 1918bb005e
3 changed files with 43 additions and 1 deletions

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@ -22,6 +22,10 @@
<body>
<release version="4.1" date="TBD" description="">
<action issue="COLLECTIONS-556" dev="tn" type="add">
Added method "SetUtils#identityHashSet()" which returns a new identity HashSet
using reference-equality instead of object-equality.
</action>
<action issue="COLLECTIONS-562" dev="tn" type="update">
Upgraded minimum java requirement to Java 6 (up from Java 5).
</action>

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@ -18,6 +18,7 @@ package org.apache.commons.collections4;
import java.util.Collection;
import java.util.Collections;
import java.util.IdentityHashMap;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
@ -151,6 +152,28 @@ public class SetUtils {
return hashCode;
}
/**
* Returns a new hash set that matches elements based on <code>==</code> not
* <code>equals()</code>.
* <p>
* <strong>This set will violate the detail of various Set contracts.</note>
* As a general rule, don't compare this set to other sets. In particular, you can't
* use decorators like {@link ListOrderedSet} on it, which silently assume that these
* contracts are fulfilled.</strong>
* <p>
* <strong>Note that the returned set is not synchronized and is not thread-safe.</strong>
* If you wish to use this set from multiple threads concurrently, you must use
* appropriate synchronization. The simplest approach is to wrap this map
* using {@link java.util.Collections#synchronizedSet(Set)}. This class may throw
* exceptions when accessed by concurrent threads without synchronization.
*
* @return a new identity hash set
* @since 4.1
*/
public static <E> Set<E> identityHashSet() {
return Collections.newSetFromMap(new IdentityHashMap<E, Boolean>());
}
//-----------------------------------------------------------------------
/**
* Returns a synchronized set backed by the given set.
@ -255,7 +278,7 @@ public class SetUtils {
* avoid non-deterministic behavior:
*
* <pre>
* Set s = SetUtils.synchronizedSet(mySet);
* Set s = SetUtils.synchronizedSortedSet(mySet);
* synchronized (s) {
* Iterator i = s.iterator();
* while (i.hasNext()) {

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@ -102,4 +102,19 @@ public class SetUtilsTest extends BulkTest {
assertEquals(0, SetUtils.hashCodeForSet(null));
}
public void testIdentityHashSet() {
Set<String> set = SetUtils.identityHashSet();
String a = new String("a");
set.add(a);
set.add(new String("b"));
set.add(a);
assertEquals(2, set.size());
set.add(new String("a"));
assertEquals(3, set.size());
set.remove(a);
assertEquals(2, set.size());
}
}