[COLLECTION-436] Added emptyIfNull methods to [Collection,Set,List,Map]Utils. Thanks to Arman Sharif for report and patch.
git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1421567 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Thomas Neidhart
parent
806c1d78d5
commit
244fe70119
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@ -22,6 +22,10 @@
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<body>
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<release version="4.0" date="TBA" description="Next release">
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<action issue="COLLECTIONS-436" dev="tn" type="add" due-to="Arman Sharif">
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Added "emptyIfNull" methods to classes "CollectionUtils", "ListUtils", "SetUtils"
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and "MapUtils".
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</action>
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<action issue="COLLECTIONS-415" dev="tn" type="add" due-to="Adrian Nistor">
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Added clarifying javadoc wrt runtime complexity of "AbstrictLinkedList#removeAll".
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</action>
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@ -115,7 +115,8 @@ public class CollectionUtils {
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* undesirable. This implementation only implements Collection.
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*/
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@SuppressWarnings("rawtypes") // we deliberately use the raw type here
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public static final Collection EMPTY_COLLECTION = UnmodifiableCollection.unmodifiableCollection(new ArrayList<Object>());
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public static final Collection EMPTY_COLLECTION =
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UnmodifiableCollection.unmodifiableCollection(new ArrayList<Object>());
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/**
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* <code>CollectionUtils</code> should not normally be instantiated.
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@ -128,6 +129,7 @@ public class CollectionUtils {
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*
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* @see #EMPTY_COLLECTION
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* @since 4.0
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* @param <T> the element type
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* @return immutable empty collection
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*/
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@SuppressWarnings("unchecked")
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@ -135,6 +137,19 @@ public class CollectionUtils {
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return EMPTY_COLLECTION;
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}
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/**
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* Returns an immutable empty collection if the argument is <code>null</code>,
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* or the argument itself otherwise.
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*
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* @param <T> the element type
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* @param collection the collection, possibly <code>null</code>
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* @return an empty collection if the argument is <code>null</code>
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*/
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@SuppressWarnings("unchecked")
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public static <T> Collection<T> emptyIfNull(Collection<T> collection) {
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return collection == null ? EMPTY_COLLECTION : collection;
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}
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/**
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* Returns a {@link Collection} containing the union of the given
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* {@link Collection}s.
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@ -188,7 +203,8 @@ public class CollectionUtils {
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* <p>
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* The cardinality of each element <i>e</i> in the returned
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* {@link Collection} will be equal to
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* <tt>max(cardinality(<i>e</i>,<i>a</i>),cardinality(<i>e</i>,<i>b</i>)) - min(cardinality(<i>e</i>,<i>a</i>),cardinality(<i>e</i>,<i>b</i>))</tt>.
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* <tt>max(cardinality(<i>e</i>,<i>a</i>),cardinality(<i>e</i>,<i>b</i>)) - min(cardinality(<i>e</i>,<i>a</i>),
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* cardinality(<i>e</i>,<i>b</i>))</tt>.
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* <p>
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* This is equivalent to
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* <tt>{@link #subtract subtract}({@link #union union(a,b)},{@link #intersection intersection(a,b)})</tt>
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@ -54,6 +54,19 @@ public class ListUtils {
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}
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//-----------------------------------------------------------------------
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/**
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* Returns an immutable empty list if the argument is <code>null</code>,
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* or the argument itself otherwise.
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*
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* @param <T> the element type
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* @param list the list, possibly <code>null</code>
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* @return an empty list if the argument is <code>null</code>
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*/
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public static <T> List<T> emptyIfNull(List<T> list) {
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return list == null ? Collections.<T>emptyList() : list;
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}
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/**
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* Returns a new list containing all elements that are contained in
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* both given lists.
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@ -85,7 +85,8 @@ public class MapUtils {
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* An empty unmodifiable sorted map.
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* This is not provided in the JDK.
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*/
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public static final SortedMap<Object, Object> EMPTY_SORTED_MAP = UnmodifiableSortedMap.unmodifiableSortedMap(new TreeMap<Object, Object>());
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public static final SortedMap<Object, Object> EMPTY_SORTED_MAP =
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UnmodifiableSortedMap.unmodifiableSortedMap(new TreeMap<Object, Object>());
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/**
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* String used to indent the verbose and debug Map prints.
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@ -1161,6 +1162,20 @@ public class MapUtils {
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}
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//-----------------------------------------------------------------------
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/**
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* Returns an immutable empty map if the argument is <code>null</code>,
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* or the argument itself otherwise.
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*
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* @param <K> the key type
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* @param <V> the value type
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* @param map the map, possibly <code>null</code>
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* @return an empty map if the argument is <code>null</code>
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*/
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public static <K,V> Map<K,V> emptyIfNull(Map<K,V> map) {
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return map == null ? Collections.<K,V>emptyMap() : map;
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}
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/**
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* Null-safe check if the specified map is empty.
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* <p>
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@ -81,6 +81,19 @@ public class SetUtils {
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}
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//-----------------------------------------------------------------------
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/**
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* Returns an immutable empty set if the argument is <code>null</code>,
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* or the argument itself otherwise.
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*
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* @param <T> the element type
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* @param set the set, possibly <code>null</code>
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* @return an empty set if the argument is <code>null</code>
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*/
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public static <T> Set<T> emptyIfNull(Set<T> set) {
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return set == null ? Collections.<T>emptySet() : set;
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}
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/**
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* Tests two sets for equality as per the <code>equals()</code> contract
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* in {@link java.util.Set#equals(java.lang.Object)}.
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@ -1341,6 +1341,13 @@ public class CollectionUtilsTest extends MockTestCase {
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assertEquals(CollectionUtils.EMPTY_COLLECTION, coll);
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}
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@Test
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public void emptyIfNull() {
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assertTrue(CollectionUtils.emptyIfNull(null).isEmpty());
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Collection<Object> collection = new ArrayList<Object>();
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assertSame(collection, CollectionUtils.emptyIfNull(collection));
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}
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/**
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* This test ensures that {@link Iterable}s are supported by {@link CollectionUtils}.
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* Specifically, it uses mocks to ensure that if the passed in
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@ -165,6 +165,13 @@ public class ListUtilsTest extends BulkTest {
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assertEquals(6, list.size());
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}
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public void testEmptyIfNull() {
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assertTrue(ListUtils.emptyIfNull(null).isEmpty());
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List<Long> list = new ArrayList<Long>();
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assertSame(list, ListUtils.emptyIfNull(list));
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}
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public void testEquals() {
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Collection<String> data = Arrays.asList( new String[] { "a", "b", "c" });
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@ -711,6 +711,14 @@ public class MapUtilsTest extends BulkTest {
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}
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//-----------------------------------------------------------------------
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public void testEmptyIfNull() {
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assertTrue(MapUtils.emptyIfNull(null).isEmpty());
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Map<Long, Long> map = new HashMap<Long, Long>();
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assertSame(map, MapUtils.emptyIfNull(map));
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}
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public void testIsEmptyWithEmptyMap() {
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Map<Object, Object> map = new HashMap<Object, Object>();
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assertEquals(true, MapUtils.isEmpty(map));
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@ -69,6 +69,13 @@ public class SetUtilsTest extends BulkTest {
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}
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}
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public void testEmptyIfNull() {
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assertTrue(SetUtils.emptyIfNull(null).isEmpty());
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Set<Long> set = new HashSet<Long>();
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assertSame(set, SetUtils.emptyIfNull(set));
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}
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public void testEquals() {
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Collection<String> data = Arrays.asList( new String[] { "a", "b", "c" });
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