Package net.sourceforge.pmd.util
Class CollectionUtil
- java.lang.Object
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- net.sourceforge.pmd.util.CollectionUtil
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public final class CollectionUtil extends Object
Generic collection-related utility functions for java.util types.- Author:
- Brian Remedios, Clément Fournier
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Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method Description static <N> boolean
all(@Nullable Iterable<? extends N> list, Predicate<? super N> predicate)
Returns true if all elements of the iterable match the predicate.static <N> boolean
any(@Nullable Iterable<? extends N> list, Predicate<? super N> predicate)
Returns true if any element of the iterable matches the predicate.static <@NonNull T>
@Nullable TasSingle(Set<@NonNull T> set)
If the set has a single element, returns it, otherwise returns null.static <K,V>
Map<K,V>associateBy(Collection<? extends @NonNull V> values, Function<? super V,? extends K> keyMapper)
static <K,V>
Map<K,V>associateByTo(Map<K,V> collector, Collection<? extends @NonNull V> values, Function<? super V,? extends K> keyMapper)
static <K,V>
Map<K,V>associateWith(Collection<? extends @NonNull K> keys, Function<? super K,? extends V> mapper)
static <K,V>
Map<K,V>associateWithTo(Map<K,V> collector, Collection<? extends @NonNull K> keys, Function<? super K,? extends V> mapper)
static <K,V>
Map<K,V>buildMap(Consumer<Map<K,V>> effect)
static <K,V>
Map<K,V>buildMap(Map<K,V> initialMap, Consumer<Map<K,V>> effect)
static <T> List<T>
concatView(List<? extends T> head, List<? extends T> tail)
Returns a list view that pretends it is the concatenation of both lists.static <T> List<T>
defensiveUnmodifiableCopy(List<? extends T> list)
Returns an unmodifiable copy of the list.static <T> Set<T>
defensiveUnmodifiableCopyToSet(Collection<? extends T> list)
static <T> Set<T>
diff(Collection<? extends T> c1, Collection<? extends T> c2, Collection<? extends T>... rest)
Returns the set difference of the first collection with the other collections.static <T> List<T>
drop(List<T> list, int n)
static <V> List<V>
emptyList()
Returns the empty list.static <V,A,C>
Cfinish(Collector<? super V,A,? extends C> collector, A acc)
Finish the accumulated value of the collector.static <@NonNull K,V>
@Nullable KgetKeyOfValue(Map<@NonNull K,V> m, V v)
Returns the key that corresponds to the given value in the map, or null if it is not contained in the map.static <T extends Enum<T>>
Set<T>immutableEnumSet(T first, T... rest)
Returns an unmodifiable set containing the given elements.static <T> Set<T>
immutableSetOf(T first, T... rest)
Returns an unmodifiable set containing the given elements.static <T> Set<T>
intersect(Collection<? extends T> c1, Collection<? extends T> c2, Collection<? extends T>... rest)
Returns the set intersection of the given collections.static @NonNull StringBuilder
joinCharsIntoStringBuilder(List<Chars> lines, String delimiter)
static <T> StringBuilder
joinOn(StringBuilder sb, Iterable<? extends T> iterable, BiConsumer<? super StringBuilder,? super T> appendItem, String delimiter)
LikeString.join(CharSequence, Iterable)
, except it appends on a preexistingStringBuilder
.static <T> List<T>
listOf(T first, T... rest)
static <T> List<T>
listOfNotNull(T t)
static <T> @NonNull List<T>
makeUnmodifiableAndNonNull(@Nullable List<? extends T> list)
static <T,R>
List<R>map(Iterable<? extends T> from, Function<? super T,? extends R> f)
Map each element of the given iterable with the given function, and accumulates it into an unmodifiable list.static <T,R>
List<R>map(Collection<? extends T> from, Function<? super T,? extends R> f)
Map each element of the given collection with the given function, and accumulates it into an unmodifiable list.static <T,R>
List<R>map(Iterator<? extends T> from, Function<? super T,? extends R> f)
Map each element of the given iterator with the given function, and accumulates it into an unmodifiable list.static <T,U,A,C>
Cmap(Collector<? super U,A,? extends C> collector, Iterable<? extends T> from, Function<? super T,? extends U> f)
Map each element of the given iterable with the given function, and accumulates it into the collector.static <T,U,A,C>
Cmap(Collector<? super U,A,? extends C> collector, Iterator<? extends T> from, Function<? super T,? extends U> f)
Map each element of the given iterator with the given function, and accumulates it into the collector.static <T,R>
List<R>map(T[] from, Function<? super T,? extends R> f)
Map each element of the given array with the given function, and accumulates it into an unmodifiable list.static <T,R>
List<@NonNull R>mapNotNull(Iterable<? extends T> from, Function<? super T,? extends @Nullable R> f)
static <K,V>
Map<K,V>mapOf(K k0, V v0)
static <K,V>
Map<K,V>mapOf(K k1, V v1, K k2, V v2)
static <K,V>
voidmergeMaps(Map<K,V> result, Map<K,V> other, BinaryOperator<V> mergeFun)
Merge the second map into the first.static <N> boolean
none(@Nullable Iterable<? extends N> list, Predicate<? super N> predicate)
Returns true if no element of the iterable matches the predicate.static <V> List<V>
plus(List<V> list, V v)
Produce a new list with the elements of the first, and one additional item.static <K,V>
Map<K,V>plus(Map<K,V> m, K k, V v)
Produce a new map with the mappings of the first, and one additional mapping.static <T> Set<T>
setOf(T first, T... rest)
Returns a set containing the given elements.static <V> Set<V>
setUnion(Collection<? extends V> set, V first, V... newElements)
Returns an unmodifiable set containing the set union of the collection, and the new elements.static <T> List<T>
take(List<T> list, int n)
static <T> Collector<T,?,List<T>>
toMutableList()
A collector that returns a mutable list.static <T> Collector<T,?,Set<T>>
toMutableSet()
A collector that returns a mutable set.static <T> Collector<T,?,org.pcollections.PSet<T>>
toPersistentSet()
A collectors that accumulates into a persistent set.static <T> Collector<T,?,List<T>>
toUnmodifiableList()
A collector that returns an unmodifiable list.static <T> Collector<T,?,Set<T>>
toUnmodifiableSet()
A collector that returns an unmodifiable set.static <T> Set<T>
union(Collection<? extends T> c1, Collection<? extends T> c2, Collection<? extends T>... rest)
Returns the set union of the given collections.static <K,V>
Map<K,V>zip(List<? extends @NonNull K> from, List<? extends @NonNull V> to)
Returns a map associating each key in the first list to its corresponding value in the second.
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Method Detail
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concatView
public static <T> List<T> concatView(List<? extends T> head, List<? extends T> tail)
Returns a list view that pretends it is the concatenation of both lists. The returned view is unmodifiable. The implementation is pretty stupid and not optimized for repeated concatenation, but should be ok for smallish chains of random-access lists.- Type Parameters:
T
- Type of elements in both lists- Parameters:
head
- Head elements (to the left)tail
- Tail elements (to the right)- Returns:
- A concatenated view
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union
@SafeVarargs public static <T> Set<T> union(Collection<? extends T> c1, Collection<? extends T> c2, Collection<? extends T>... rest)
Returns the set union of the given collections.- Parameters:
c1
- First collectionc2
- Second collection- Returns:
- Union of both arguments
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intersect
@SafeVarargs public static <T> Set<T> intersect(Collection<? extends T> c1, Collection<? extends T> c2, Collection<? extends T>... rest)
Returns the set intersection of the given collections.- Parameters:
c1
- First collectionc2
- Second collection- Returns:
- Intersection of both arguments
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diff
@SafeVarargs public static <T> Set<T> diff(Collection<? extends T> c1, Collection<? extends T> c2, Collection<? extends T>... rest)
Returns the set difference of the first collection with the other collections.- Parameters:
c1
- First collectionc2
- Second collection- Returns:
- Difference of arguments
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setOf
@SafeVarargs public static <T> Set<T> setOf(T first, T... rest)
Returns a set containing the given elements. No guarantee is made about mutability.- Parameters:
first
- First elementrest
- Following elements
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immutableSetOf
@SafeVarargs public static <T> Set<T> immutableSetOf(T first, T... rest)
Returns an unmodifiable set containing the given elements.- Parameters:
first
- First elementrest
- Following elements
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immutableEnumSet
@SafeVarargs public static <T extends Enum<T>> Set<T> immutableEnumSet(T first, T... rest)
Returns an unmodifiable set containing the given elements.- Parameters:
first
- First elementrest
- Following elements
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listOf
@SafeVarargs public static <T> List<T> listOf(T first, T... rest)
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mapOf
public static <K,V> Map<K,V> mapOf(K k0, V v0)
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mapOf
public static <K,V> Map<K,V> mapOf(K k1, V v1, K k2, V v2)
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mapNotNull
public static <T,R> List<@NonNull R> mapNotNull(Iterable<? extends T> from, Function<? super T,? extends @Nullable R> f)
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plus
public static <K,V> Map<K,V> plus(Map<K,V> m, K k, V v)
Produce a new map with the mappings of the first, and one additional mapping. The returned map may be unmodifiable.
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plus
public static <V> List<V> plus(List<V> list, V v)
Produce a new list with the elements of the first, and one additional item. The returned list is immutable.
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emptyList
public static <V> List<V> emptyList()
Returns the empty list.
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setUnion
@SafeVarargs public static <V> Set<V> setUnion(Collection<? extends V> set, V first, V... newElements)
Returns an unmodifiable set containing the set union of the collection, and the new elements.
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getKeyOfValue
public static <@NonNull K,V> @Nullable K getKeyOfValue(Map<@NonNull K,V> m, V v)
Returns the key that corresponds to the given value in the map, or null if it is not contained in the map.- Type Parameters:
K
- Type of keysV
- Type of values- Parameters:
m
- Mapv
- Value- Throws:
NullPointerException
- If the entry is found, but the key is nullNullPointerException
- If the map is null
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zip
public static <K,V> Map<K,V> zip(List<? extends @NonNull K> from, List<? extends @NonNull V> to)
Returns a map associating each key in the first list to its corresponding value in the second.- Throws:
IllegalArgumentException
- If the list size are mismatchedNullPointerException
- If either of the parameter is null, or any of the keys or values are null
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associateWith
public static <K,V> Map<K,V> associateWith(Collection<? extends @NonNull K> keys, Function<? super K,? extends V> mapper)
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associateWithTo
public static <K,V> Map<K,V> associateWithTo(Map<K,V> collector, Collection<? extends @NonNull K> keys, Function<? super K,? extends V> mapper)
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associateBy
public static <K,V> Map<K,V> associateBy(Collection<? extends @NonNull V> values, Function<? super V,? extends K> keyMapper)
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associateByTo
public static <K,V> Map<K,V> associateByTo(Map<K,V> collector, Collection<? extends @NonNull V> values, Function<? super V,? extends K> keyMapper)
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map
public static <T,R> List<R> map(Collection<? extends T> from, Function<? super T,? extends R> f)
Map each element of the given collection with the given function, and accumulates it into an unmodifiable list.
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map
public static <T,R> List<R> map(Iterable<? extends T> from, Function<? super T,? extends R> f)
Map each element of the given iterable with the given function, and accumulates it into an unmodifiable list.
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map
public static <T,R> List<R> map(T[] from, Function<? super T,? extends R> f)
Map each element of the given array with the given function, and accumulates it into an unmodifiable list.
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map
public static <T,R> List<R> map(Iterator<? extends T> from, Function<? super T,? extends R> f)
Map each element of the given iterator with the given function, and accumulates it into an unmodifiable list.
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map
public static <T,U,A,C> C map(Collector<? super U,A,? extends C> collector, Iterable<? extends T> from, Function<? super T,? extends U> f)
Map each element of the given iterable with the given function, and accumulates it into the collector.
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map
public static <T,U,A,C> C map(Collector<? super U,A,? extends C> collector, Iterator<? extends T> from, Function<? super T,? extends U> f)
Map each element of the given iterator with the given function, and accumulates it into the collector.
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toMutableList
public static <T> Collector<T,?,List<T>> toMutableList()
A collector that returns a mutable list. This contrasts withCollectors.toList()
, which makes no guarantee about the mutability of the list.- Type Parameters:
T
- Type of accumulated values
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toMutableSet
public static <T> Collector<T,?,Set<T>> toMutableSet()
A collector that returns a mutable set. This contrasts withCollectors.toSet()
, which makes no guarantee about the mutability of the set. The set preserves insertion order.- Type Parameters:
T
- Type of accumulated values
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toUnmodifiableList
public static <T> Collector<T,?,List<T>> toUnmodifiableList()
A collector that returns an unmodifiable list. This contrasts withCollectors.toList()
, which makes no guarantee about the mutability of the list.Collectors::toUnmodifiableList
was only added in JDK 9.- Type Parameters:
T
- Type of accumulated values
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toUnmodifiableSet
public static <T> Collector<T,?,Set<T>> toUnmodifiableSet()
A collector that returns an unmodifiable set. This contrasts withCollectors.toSet()
, which makes no guarantee about the mutability of the set.Collectors::toUnmodifiableSet
was only added in JDK 9. The set preserves insertion order.- Type Parameters:
T
- Type of accumulated values
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toPersistentSet
public static <T> Collector<T,?,org.pcollections.PSet<T>> toPersistentSet()
A collectors that accumulates into a persistent set.- Type Parameters:
T
- Type of accumulated values
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finish
public static <V,A,C> C finish(Collector<? super V,A,? extends C> collector, A acc)
Finish the accumulated value of the collector.
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listOfNotNull
public static <T> List<T> listOfNotNull(T t)
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any
public static <N> boolean any(@Nullable Iterable<? extends N> list, Predicate<? super N> predicate)
Returns true if any element of the iterable matches the predicate. Return false if the list is null or empty.
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all
public static <N> boolean all(@Nullable Iterable<? extends N> list, Predicate<? super N> predicate)
Returns true if all elements of the iterable match the predicate. Return true if the list is null or empty.
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none
public static <N> boolean none(@Nullable Iterable<? extends N> list, Predicate<? super N> predicate)
Returns true if no element of the iterable matches the predicate. Return true if the list is null or empty.
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asSingle
public static <@NonNull T> @Nullable T asSingle(Set<@NonNull T> set)
If the set has a single element, returns it, otherwise returns null. Obviously the set should not contain null elements.
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defensiveUnmodifiableCopy
public static <T> List<T> defensiveUnmodifiableCopy(List<? extends T> list)
Returns an unmodifiable copy of the list. This is to be preferred toCollections.unmodifiableList(List)
if you don't trust the source of the list, because no one holds a reference to the buffer except the returned unmodifiable list.- Type Parameters:
T
- Type of items- Parameters:
list
- A list
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defensiveUnmodifiableCopyToSet
public static <T> Set<T> defensiveUnmodifiableCopyToSet(Collection<? extends T> list)
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joinOn
public static <T> StringBuilder joinOn(StringBuilder sb, Iterable<? extends T> iterable, BiConsumer<? super StringBuilder,? super T> appendItem, String delimiter)
LikeString.join(CharSequence, Iterable)
, except it appends on a preexistingStringBuilder
. The result value is that StringBuilder.
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joinCharsIntoStringBuilder
public static @NonNull StringBuilder joinCharsIntoStringBuilder(List<Chars> lines, String delimiter)
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mergeMaps
public static <K,V> void mergeMaps(Map<K,V> result, Map<K,V> other, BinaryOperator<V> mergeFun)
Merge the second map into the first. If some keys are in common, merge them using the merge function, likeMap.merge(Object, Object, BiFunction)
.
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