Collections (Java SE 9 & JDK 9 ) (original) (raw)

Field Summary

Fields

Modifier and Type	Field	Description
static List	EMPTY_LIST	The empty list (immutable).
static Map	EMPTY_MAP	The empty map (immutable).
static Set	EMPTY_SET	The empty set (immutable).

Method Summary

All Methods Static Methods Concrete Methods

Modifier and Type	Method	Description
static boolean	addAll(Collection<? super T> c, T... elements)	Adds all of the specified elements to the specified collection.
static Queue	asLifoQueue(Deque deque)	Returns a view of a Deque as a Last-in-first-out (Lifo)Queue.
static int	binarySearch(List<? extends Comparable<? super T>> list, T key)	Searches the specified list for the specified object using the binary search algorithm.
static int	binarySearch(List<? extends T> list, T key,Comparator<? super T> c)	Searches the specified list for the specified object using the binary search algorithm.
static Collection	checkedCollection(Collection c,Class type)	Returns a dynamically typesafe view of the specified collection.
static List	checkedList(List list,Class type)	Returns a dynamically typesafe view of the specified list.
static <K,V> Map<K,V>	checkedMap(Map<K,V> m,Class keyType,Class valueType)	Returns a dynamically typesafe view of the specified map.
static <K,V> NavigableMap<K,V>	checkedNavigableMap(NavigableMap<K,V> m,Class keyType,Class valueType)	Returns a dynamically typesafe view of the specified navigable map.
static NavigableSet	checkedNavigableSet(NavigableSet s,Class type)	Returns a dynamically typesafe view of the specified navigable set.
static Queue	checkedQueue(Queue queue,Class type)	Returns a dynamically typesafe view of the specified queue.
static Set	checkedSet(Set s,Class type)	Returns a dynamically typesafe view of the specified set.
static <K,V> SortedMap<K,V>	checkedSortedMap(SortedMap<K,V> m,Class keyType,Class valueType)	Returns a dynamically typesafe view of the specified sorted map.
static SortedSet	checkedSortedSet(SortedSet s,Class type)	Returns a dynamically typesafe view of the specified sorted set.
static void	copy(List<? super T> dest,List<? extends T> src)	Copies all of the elements from one list into another.
static boolean	disjoint(Collection c1,[Collection](../../java/util/Collection.html "interface in java.util") c2)	Returns true if the two specified collections have no elements in common.
static Enumeration	emptyEnumeration()	Returns an enumeration that has no elements.
static Iterator	emptyIterator()	Returns an iterator that has no elements.
static List	emptyList()	Returns an empty list (immutable).
static ListIterator	emptyListIterator()	Returns a list iterator that has no elements.
static <K,V> Map<K,V>	emptyMap()	Returns an empty map (immutable).
static <K,V> NavigableMap<K,V>	emptyNavigableMap()	Returns an empty navigable map (immutable).
static NavigableSet	emptyNavigableSet()	Returns an empty navigable set (immutable).
static Set	emptySet()	Returns an empty set (immutable).
static <K,V> SortedMap<K,V>	emptySortedMap()	Returns an empty sorted map (immutable).
static SortedSet	emptySortedSet()	Returns an empty sorted set (immutable).
static Enumeration	enumeration(Collection c)	Returns an enumeration over the specified collection.
static void	fill(List<? super T> list, T obj)	Replaces all of the elements of the specified list with the specified element.
static int	frequency(Collection<?> c,Object o)	Returns the number of elements in the specified collection equal to the specified object.
static int	indexOfSubList(List source,[List](../../java/util/List.html "interface in java.util") target)	Returns the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.
static int	lastIndexOfSubList(List source,[List](../../java/util/List.html "interface in java.util") target)	Returns the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.
static ArrayList	list(Enumeration e)	Returns an array list containing the elements returned by the specified enumeration in the order they are returned by the enumeration.
static <T extends Object & Comparable<? super T>>T	max(Collection<? extends T> coll)	Returns the maximum element of the given collection, according to the_natural ordering_ of its elements.
static T	max(Collection<? extends T> coll,Comparator<? super T> comp)	Returns the maximum element of the given collection, according to the order induced by the specified comparator.
static <T extends Object & Comparable<? super T>>T	min(Collection<? extends T> coll)	Returns the minimum element of the given collection, according to the_natural ordering_ of its elements.
static T	min(Collection<? extends T> coll,Comparator<? super T> comp)	Returns the minimum element of the given collection, according to the order induced by the specified comparator.
static List	nCopies(int n, T o)	Returns an immutable list consisting of n copies of the specified object.
static Set	newSetFromMap(Map<E,Boolean> map)	Returns a set backed by the specified map.
static boolean	replaceAll(List list, T oldVal, T newVal)	Replaces all occurrences of one specified value in a list with another.
static void	reverse(List<?> list)	Reverses the order of the elements in the specified list.
static Comparator	reverseOrder()	Returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement theComparable interface.
static Comparator	reverseOrder(Comparator cmp)	Returns a comparator that imposes the reverse ordering of the specified comparator.
static void	rotate(List<?> list, int distance)	Rotates the elements in the specified list by the specified distance.
static void	shuffle(List<?> list)	Randomly permutes the specified list using a default source of randomness.
static void	shuffle(List<?> list,Random rnd)	Randomly permute the specified list using the specified source of randomness.
static Set	singleton(T o)	Returns an immutable set containing only the specified object.
static List	singletonList(T o)	Returns an immutable list containing only the specified object.
static <K,V> Map<K,V>	singletonMap(K key, V value)	Returns an immutable map, mapping only the specified key to the specified value.
static <T extends Comparable<? super T>>void	sort(List list)	Sorts the specified list into ascending order, according to thenatural ordering of its elements.
static void	sort(List list,Comparator<? super T> c)	Sorts the specified list according to the order induced by the specified comparator.
static void	swap(List<?> list, int i, int j)	Swaps the elements at the specified positions in the specified list.
static Collection	synchronizedCollection(Collection c)	Returns a synchronized (thread-safe) collection backed by the specified collection.
static List	synchronizedList(List list)	Returns a synchronized (thread-safe) list backed by the specified list.
static <K,V> Map<K,V>	synchronizedMap(Map<K,V> m)	Returns a synchronized (thread-safe) map backed by the specified map.
static <K,V> NavigableMap<K,V>	synchronizedNavigableMap(NavigableMap<K,V> m)	Returns a synchronized (thread-safe) navigable map backed by the specified navigable map.
static NavigableSet	synchronizedNavigableSet(NavigableSet s)	Returns a synchronized (thread-safe) navigable set backed by the specified navigable set.
static Set	synchronizedSet(Set s)	Returns a synchronized (thread-safe) set backed by the specified set.
static <K,V> SortedMap<K,V>	synchronizedSortedMap(SortedMap<K,V> m)	Returns a synchronized (thread-safe) sorted map backed by the specified sorted map.
static SortedSet	synchronizedSortedSet(SortedSet s)	Returns a synchronized (thread-safe) sorted set backed by the specified sorted set.
static Collection	unmodifiableCollection(Collection<? extends T> c)	Returns an unmodifiable view of the specified collection.
static List	unmodifiableList(List<? extends T> list)	Returns an unmodifiable view of the specified list.
static <K,V> Map<K,V>	unmodifiableMap(Map<? extends K,? extends V> m)	Returns an unmodifiable view of the specified map.
static <K,V> NavigableMap<K,V>	unmodifiableNavigableMap(NavigableMap<K,? extends V> m)	Returns an unmodifiable view of the specified navigable map.
static NavigableSet	unmodifiableNavigableSet(NavigableSet s)	Returns an unmodifiable view of the specified navigable set.
static Set	unmodifiableSet(Set<? extends T> s)	Returns an unmodifiable view of the specified set.
static <K,V> SortedMap<K,V>	unmodifiableSortedMap(SortedMap<K,? extends V> m)	Returns an unmodifiable view of the specified sorted map.
static SortedSet	unmodifiableSortedSet(SortedSet s)	Returns an unmodifiable view of the specified sorted set.

   * ### Methods inherited from class java.lang.[Object](../../java/lang/Object.html "class in java.lang")  
   `[clone](../../java/lang/Object.html#clone--), [equals](../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../java/lang/Object.html#finalize--), [getClass](../../java/lang/Object.html#getClass--), [hashCode](../../java/lang/Object.html#hashCode--), [notify](../../java/lang/Object.html#notify--), [notifyAll](../../java/lang/Object.html#notifyAll--), [toString](../../java/lang/Object.html#toString--), [wait](../../java/lang/Object.html#wait--), [wait](../../java/lang/Object.html#wait-long-), [wait](../../java/lang/Object.html#wait-long-int-)`

Field Detail

 * #### EMPTY\_SET  
 public static final [Set](../../java/util/Set.html "interface in java.util") EMPTY_SET  
 The empty set (immutable). This set is serializable.  
 See Also:  
 [emptySet()](../../java/util/Collections.html#emptySet--)  
 * #### EMPTY\_LIST  
 public static final [List](../../java/util/List.html "interface in java.util") EMPTY_LIST  
 The empty list (immutable). This list is serializable.  
 See Also:  
 [emptyList()](../../java/util/Collections.html#emptyList--)  
 * #### EMPTY\_MAP  
 public static final [Map](../../java/util/Map.html "interface in java.util") EMPTY_MAP  
 The empty map (immutable). This map is serializable.  
 Since:  
 1.3  
 See Also:  
 [emptyMap()](../../java/util/Collections.html#emptyMap--)

Method Detail

* #### sort  
public static <T extends [Comparable](../../java/lang/Comparable.html "interface in java.lang")<? super T>> void sort([List](../../java/util/List.html "interface in java.util")<T> list)  
Sorts the specified list into ascending order, according to the[natural ordering](../../java/lang/Comparable.html "interface in java.lang") of its elements. All elements in the list must implement the [Comparable](../../java/lang/Comparable.html "interface in java.lang") interface. Furthermore, all elements in the list must be_mutually comparable_ (that is, `e1.compareTo(e2)` must not throw a `ClassCastException` for any elements`e1` and `e2` in the list).  
This sort is guaranteed to be _stable_: equal elements will not be reordered as a result of the sort.  
The specified list must be modifiable, but need not be resizable.  
Implementation Note:  
This implementation defers to the [List.sort(Comparator)](../../java/util/List.html#sort-java.util.Comparator-) method using the specified list and a `null` comparator.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list to be sorted.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the list contains elements that are not_mutually comparable_ (for example, strings and integers).  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list's list-iterator does not support the `set` operation.  
`[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- (optional) if the implementation detects that the natural ordering of the list elements is found to violate the [Comparable](../../java/lang/Comparable.html "interface in java.lang") contract  
See Also:  
[List.sort(Comparator)](../../java/util/List.html#sort-java.util.Comparator-)  
* #### sort  
public static <T> void sort([List](../../java/util/List.html "interface in java.util")<T> list,  
                            [Comparator](../../java/util/Comparator.html "interface in java.util")<? super T> c)  
Sorts the specified list according to the order induced by the specified comparator. All elements in the list must be _mutually comparable_ using the specified comparator (that is,`c.compare(e1, e2)` must not throw a `ClassCastException` for any elements `e1` and `e2` in the list).  
This sort is guaranteed to be _stable_: equal elements will not be reordered as a result of the sort.  
The specified list must be modifiable, but need not be resizable.  
Implementation Note:  
This implementation defers to the [List.sort(Comparator)](../../java/util/List.html#sort-java.util.Comparator-) method using the specified list and comparator.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list to be sorted.  
`c` \- the comparator to determine the order of the list. A`null` value indicates that the elements' _natural ordering_ should be used.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the list contains elements that are not_mutually comparable_ using the specified comparator.  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list's list-iterator does not support the `set` operation.  
`[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- (optional) if the comparator is found to violate the [Comparator](../../java/util/Comparator.html "interface in java.util") contract  
See Also:  
[List.sort(Comparator)](../../java/util/List.html#sort-java.util.Comparator-)  
* #### binarySearch  
public static <T> int binarySearch([List](../../java/util/List.html "interface in java.util")<? extends [Comparable](../../java/lang/Comparable.html "interface in java.lang")<? super T>> list,  
                                   T key)  
Searches the specified list for the specified object using the binary search algorithm. The list must be sorted into ascending order according to the [natural ordering](../../java/lang/Comparable.html "interface in java.lang") of its elements (as by the [sort(List)](../../java/util/Collections.html#sort-java.util.List-) method) prior to making this call. If it is not sorted, the results are undefined. If the list contains multiple elements equal to the specified object, there is no guarantee which one will be found.  
This method runs in log(n) time for a "random access" list (which provides near-constant-time positional access). If the specified list does not implement the [RandomAccess](../../java/util/RandomAccess.html "interface in java.util") interface and is large, this method will do an iterator-based binary search that performs O(n) link traversals and O(log n) element comparisons.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list to be searched.  
`key` \- the key to be searched for.  
Returns:  
the index of the search key, if it is contained in the list; otherwise, `(-(_insertion point_) - 1)`. The_insertion point_ is defined as the point at which the key would be inserted into the list: the index of the first element greater than the key, or `list.size()` if all elements in the list are less than the specified key. Note that this guarantees that the return value will be >= 0 if and only if the key is found.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the list contains elements that are not_mutually comparable_ (for example, strings and integers), or the search key is not mutually comparable with the elements of the list.  
* #### binarySearch  
public static <T> int binarySearch([List](../../java/util/List.html "interface in java.util")<? extends T> list,  
                                   T key,  
                                   [Comparator](../../java/util/Comparator.html "interface in java.util")<? super T> c)  
Searches the specified list for the specified object using the binary search algorithm. The list must be sorted into ascending order according to the specified comparator (as by the[sort(List, Comparator)](../../java/util/Collections.html#sort-java.util.List-java.util.Comparator-) method), prior to making this call. If it is not sorted, the results are undefined. If the list contains multiple elements equal to the specified object, there is no guarantee which one will be found.  
This method runs in log(n) time for a "random access" list (which provides near-constant-time positional access). If the specified list does not implement the [RandomAccess](../../java/util/RandomAccess.html "interface in java.util") interface and is large, this method will do an iterator-based binary search that performs O(n) link traversals and O(log n) element comparisons.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list to be searched.  
`key` \- the key to be searched for.  
`c` \- the comparator by which the list is ordered. A `null` value indicates that the elements'[natural ordering](../../java/lang/Comparable.html "interface in java.lang") should be used.  
Returns:  
the index of the search key, if it is contained in the list; otherwise, `(-(_insertion point_) - 1)`. The_insertion point_ is defined as the point at which the key would be inserted into the list: the index of the first element greater than the key, or `list.size()` if all elements in the list are less than the specified key. Note that this guarantees that the return value will be >= 0 if and only if the key is found.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the list contains elements that are not_mutually comparable_ using the specified comparator, or the search key is not mutually comparable with the elements of the list using this comparator.  
* #### reverse  
public static void reverse([List](../../java/util/List.html "interface in java.util")<?> list)  
Reverses the order of the elements in the specified list.  
 This method runs in linear time.  
Parameters:  
`list` \- the list whose elements are to be reversed.  
Throws:  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list or its list-iterator does not support the `set` operation.  
* #### shuffle  
public static void shuffle([List](../../java/util/List.html "interface in java.util")<?> list)  
Randomly permutes the specified list using a default source of randomness. All permutations occur with approximately equal likelihood.  
The hedge "approximately" is used in the foregoing description because default source of randomness is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm would choose permutations with perfect uniformity.  
This implementation traverses the list backwards, from the last element up to the second, repeatedly swapping a randomly selected element into the "current position". Elements are randomly selected from the portion of the list that runs from the first element to the current position, inclusive.  
This method runs in linear time. If the specified list does not implement the [RandomAccess](../../java/util/RandomAccess.html "interface in java.util") interface and is large, this implementation dumps the specified list into an array before shuffling it, and dumps the shuffled array back into the list. This avoids the quadratic behavior that would result from shuffling a "sequential access" list in place.  
Parameters:  
`list` \- the list to be shuffled.  
Throws:  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list or its list-iterator does not support the `set` operation.  
* #### shuffle  
public static void shuffle([List](../../java/util/List.html "interface in java.util")<?> list,  
                           [Random](../../java/util/Random.html "class in java.util") rnd)  
Randomly permute the specified list using the specified source of randomness. All permutations occur with equal likelihood assuming that the source of randomness is fair.  
 This implementation traverses the list backwards, from the last element up to the second, repeatedly swapping a randomly selected element into the "current position". Elements are randomly selected from the portion of the list that runs from the first element to the current position, inclusive.  
 This method runs in linear time. If the specified list does not implement the [RandomAccess](../../java/util/RandomAccess.html "interface in java.util") interface and is large, this implementation dumps the specified list into an array before shuffling it, and dumps the shuffled array back into the list. This avoids the quadratic behavior that would result from shuffling a "sequential access" list in place.  
Parameters:  
`list` \- the list to be shuffled.  
`rnd` \- the source of randomness to use to shuffle the list.  
Throws:  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list or its list-iterator does not support the `set` operation.  
* #### swap  
public static void swap([List](../../java/util/List.html "interface in java.util")<?> list,  
                        int i,  
                        int j)  
Swaps the elements at the specified positions in the specified list. (If the specified positions are equal, invoking this method leaves the list unchanged.)  
Parameters:  
`list` \- The list in which to swap elements.  
`i` \- the index of one element to be swapped.  
`j` \- the index of the other element to be swapped.  
Throws:  
`[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang")` \- if either `i` or `j` is out of range (i < 0 || i >= list.size() || j < 0 || j >= list.size()).  
Since:  
1.4  
* #### fill  
public static <T> void fill([List](../../java/util/List.html "interface in java.util")<? super T> list,  
                            T obj)  
Replaces all of the elements of the specified list with the specified element.  
 This method runs in linear time.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list to be filled with the specified element.  
`obj` \- The element with which to fill the specified list.  
Throws:  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list or its list-iterator does not support the `set` operation.  
* #### copy  
public static <T> void copy([List](../../java/util/List.html "interface in java.util")<? super T> dest,  
                            [List](../../java/util/List.html "interface in java.util")<? extends T> src)  
Copies all of the elements from one list into another. After the operation, the index of each copied element in the destination list will be identical to its index in the source list. The destination list's size must be greater than or equal to the source list's size. If it is greater, the remaining elements in the destination list are unaffected.  
 This method runs in linear time.  
Type Parameters:  
`T` \- the class of the objects in the lists  
Parameters:  
`dest` \- The destination list.  
`src` \- The source list.  
Throws:  
`[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang")` \- if the destination list is too small to contain the entire source List.  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the destination list's list-iterator does not support the `set` operation.  
* #### min  
public static <T extends [Object](../../java/lang/Object.html "class in java.lang") & [Comparable](../../java/lang/Comparable.html "interface in java.lang")<? super T>> T min([Collection](../../java/util/Collection.html "interface in java.util")<? extends T> coll)  
Returns the minimum element of the given collection, according to the_natural ordering_ of its elements. All elements in the collection must implement the `Comparable` interface. Furthermore, all elements in the collection must be _mutually comparable_ (that is, `e1.compareTo(e2)` must not throw a`ClassCastException` for any elements `e1` and`e2` in the collection).  
 This method iterates over the entire collection, hence it requires time proportional to the size of the collection.  
Type Parameters:  
`T` \- the class of the objects in the collection  
Parameters:  
`coll` \- the collection whose minimum element is to be determined.  
Returns:  
the minimum element of the given collection, according to the _natural ordering_ of its elements.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the collection contains elements that are not _mutually comparable_ (for example, strings and integers).  
`[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util")` \- if the collection is empty.  
See Also:  
[Comparable](../../java/lang/Comparable.html "interface in java.lang")  
* #### min  
public static <T> T min([Collection](../../java/util/Collection.html "interface in java.util")<? extends T> coll,  
                        [Comparator](../../java/util/Comparator.html "interface in java.util")<? super T> comp)  
Returns the minimum element of the given collection, according to the order induced by the specified comparator. All elements in the collection must be _mutually comparable_ by the specified comparator (that is, `comp.compare(e1, e2)` must not throw a`ClassCastException` for any elements `e1` and`e2` in the collection).  
 This method iterates over the entire collection, hence it requires time proportional to the size of the collection.  
Type Parameters:  
`T` \- the class of the objects in the collection  
Parameters:  
`coll` \- the collection whose minimum element is to be determined.  
`comp` \- the comparator with which to determine the minimum element. A `null` value indicates that the elements' _natural ordering_ should be used.  
Returns:  
the minimum element of the given collection, according to the specified comparator.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the collection contains elements that are not _mutually comparable_ using the specified comparator.  
`[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util")` \- if the collection is empty.  
See Also:  
[Comparable](../../java/lang/Comparable.html "interface in java.lang")  
* #### max  
public static <T extends [Object](../../java/lang/Object.html "class in java.lang") & [Comparable](../../java/lang/Comparable.html "interface in java.lang")<? super T>> T max([Collection](../../java/util/Collection.html "interface in java.util")<? extends T> coll)  
Returns the maximum element of the given collection, according to the_natural ordering_ of its elements. All elements in the collection must implement the `Comparable` interface. Furthermore, all elements in the collection must be _mutually comparable_ (that is, `e1.compareTo(e2)` must not throw a`ClassCastException` for any elements `e1` and`e2` in the collection).  
 This method iterates over the entire collection, hence it requires time proportional to the size of the collection.  
Type Parameters:  
`T` \- the class of the objects in the collection  
Parameters:  
`coll` \- the collection whose maximum element is to be determined.  
Returns:  
the maximum element of the given collection, according to the _natural ordering_ of its elements.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the collection contains elements that are not _mutually comparable_ (for example, strings and integers).  
`[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util")` \- if the collection is empty.  
See Also:  
[Comparable](../../java/lang/Comparable.html "interface in java.lang")  
* #### max  
public static <T> T max([Collection](../../java/util/Collection.html "interface in java.util")<? extends T> coll,  
                        [Comparator](../../java/util/Comparator.html "interface in java.util")<? super T> comp)  
Returns the maximum element of the given collection, according to the order induced by the specified comparator. All elements in the collection must be _mutually comparable_ by the specified comparator (that is, `comp.compare(e1, e2)` must not throw a`ClassCastException` for any elements `e1` and`e2` in the collection).  
 This method iterates over the entire collection, hence it requires time proportional to the size of the collection.  
Type Parameters:  
`T` \- the class of the objects in the collection  
Parameters:  
`coll` \- the collection whose maximum element is to be determined.  
`comp` \- the comparator with which to determine the maximum element. A `null` value indicates that the elements' _natural ordering_ should be used.  
Returns:  
the maximum element of the given collection, according to the specified comparator.  
Throws:  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the collection contains elements that are not _mutually comparable_ using the specified comparator.  
`[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util")` \- if the collection is empty.  
See Also:  
[Comparable](../../java/lang/Comparable.html "interface in java.lang")  
* #### rotate  
public static void rotate([List](../../java/util/List.html "interface in java.util")<?> list,  
                          int distance)  
Rotates the elements in the specified list by the specified distance. After calling this method, the element at index `i` will be the element previously at index `(i - distance)` mod`list.size()`, for all values of `i` between `0` and `list.size()-1`, inclusive. (This method has no effect on the size of the list.)  
For example, suppose `list` comprises` [t, a, n, k, s]`. After invoking `Collections.rotate(list, 1)` (or`Collections.rotate(list, -4)`), `list` will comprise`[s, t, a, n, k]`.  
Note that this method can usefully be applied to sublists to move one or more elements within a list while preserving the order of the remaining elements. For example, the following idiom moves the element at index `j` forward to position`k` (which must be greater than or equal to `j`):  
     Collections.rotate(list.subList(j, k+1), -1);  
       
 To make this concrete, suppose `list` comprises`[a, b, c, d, e]`. To move the element at index `1` (`b`) forward two positions, perform the following invocation:  
     Collections.rotate(l.subList(1, 4), -1);  
       
 The resulting list is `[a, c, d, b, e]`.  
To move more than one element forward, increase the absolute value of the rotation distance. To move elements backward, use a positive shift distance.  
If the specified list is small or implements the [RandomAccess](../../java/util/RandomAccess.html "interface in java.util") interface, this implementation exchanges the first element into the location it should go, and then repeatedly exchanges the displaced element into the location it should go until a displaced element is swapped into the first element. If necessary, the process is repeated on the second and successive elements, until the rotation is complete. If the specified list is large and doesn't implement the`RandomAccess` interface, this implementation breaks the list into two sublist views around index `-distance mod size`. Then the [reverse(List)](../../java/util/Collections.html#reverse-java.util.List-) method is invoked on each sublist view, and finally it is invoked on the entire list. For a more complete description of both algorithms, see Section 2.3 of Jon Bentley's_Programming Pearls_ (Addison-Wesley, 1986).  
Parameters:  
`list` \- the list to be rotated.  
`distance` \- the distance to rotate the list. There are no constraints on this value; it may be zero, negative, or greater than `list.size()`.  
Throws:  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list or its list-iterator does not support the `set` operation.  
Since:  
1.4  
* #### replaceAll  
public static <T> boolean replaceAll([List](../../java/util/List.html "interface in java.util")<T> list,  
                                     T oldVal,  
                                     T newVal)  
Replaces all occurrences of one specified value in a list with another. More formally, replaces with `newVal` each element `e` in `list` such that`(oldVal==null ? e==null : oldVal.equals(e))`. (This method has no effect on the size of the list.)  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list in which replacement is to occur.  
`oldVal` \- the old value to be replaced.  
`newVal` \- the new value with which `oldVal` is to be replaced.  
Returns:  
`true` if `list` contained one or more elements`e` such that`(oldVal==null ? e==null : oldVal.equals(e))`.  
Throws:  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the specified list or its list-iterator does not support the `set` operation.  
Since:  
1.4  
* #### indexOfSubList  
public static int indexOfSubList([List](../../java/util/List.html "interface in java.util")<?> source,  
                                 [List](../../java/util/List.html "interface in java.util")<?> target)  
Returns the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence. More formally, returns the lowest index `i` such that `source.subList(i, i+target.size()).equals(target)`, or -1 if there is no such index. (Returns -1 if`target.size() > source.size()`)  
This implementation uses the "brute force" technique of scanning over the source list, looking for a match with the target at each location in turn.  
Parameters:  
`source` \- the list in which to search for the first occurrence of `target`.  
`target` \- the list to search for as a subList of `source`.  
Returns:  
the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.  
Since:  
1.4  
* #### lastIndexOfSubList  
public static int lastIndexOfSubList([List](../../java/util/List.html "interface in java.util")<?> source,  
                                     [List](../../java/util/List.html "interface in java.util")<?> target)  
Returns the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence. More formally, returns the highest index `i` such that `source.subList(i, i+target.size()).equals(target)`, or -1 if there is no such index. (Returns -1 if`target.size() > source.size()`)  
This implementation uses the "brute force" technique of iterating over the source list, looking for a match with the target at each location in turn.  
Parameters:  
`source` \- the list in which to search for the last occurrence of `target`.  
`target` \- the list to search for as a subList of `source`.  
Returns:  
the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.  
Since:  
1.4  
* #### unmodifiableCollection  
public static <T> [Collection](../../java/util/Collection.html "interface in java.util")<T> unmodifiableCollection([Collection](../../java/util/Collection.html "interface in java.util")<? extends T> c)  
Returns an unmodifiable view of the specified collection. This method allows modules to provide users with "read-only" access to internal collections. Query operations on the returned collection "read through" to the specified collection, and attempts to modify the returned collection, whether direct or via its iterator, result in an`UnsupportedOperationException`.  
 The returned collection does _not_ pass the hashCode and equals operations through to the backing collection, but relies on`Object`'s `equals` and `hashCode` methods. This is necessary to preserve the contracts of these operations in the case that the backing collection is a set or a list.  
 The returned collection will be serializable if the specified collection is serializable.  
Type Parameters:  
`T` \- the class of the objects in the collection  
Parameters:  
`c` \- the collection for which an unmodifiable view is to be returned.  
Returns:  
an unmodifiable view of the specified collection.  
* #### unmodifiableSet  
public static <T> [Set](../../java/util/Set.html "interface in java.util")<T> unmodifiableSet([Set](../../java/util/Set.html "interface in java.util")<? extends T> s)  
Returns an unmodifiable view of the specified set. This method allows modules to provide users with "read-only" access to internal sets. Query operations on the returned set "read through" to the specified set, and attempts to modify the returned set, whether direct or via its iterator, result in an `UnsupportedOperationException`.  
 The returned set will be serializable if the specified set is serializable.  
Type Parameters:  
`T` \- the class of the objects in the set  
Parameters:  
`s` \- the set for which an unmodifiable view is to be returned.  
Returns:  
an unmodifiable view of the specified set.  
* #### unmodifiableSortedSet  
public static <T> [SortedSet](../../java/util/SortedSet.html "interface in java.util")<T> unmodifiableSortedSet([SortedSet](../../java/util/SortedSet.html "interface in java.util")<T> s)  
Returns an unmodifiable view of the specified sorted set. This method allows modules to provide users with "read-only" access to internal sorted sets. Query operations on the returned sorted set "read through" to the specified sorted set. Attempts to modify the returned sorted set, whether direct, via its iterator, or via its`subSet`, `headSet`, or `tailSet` views, result in an `UnsupportedOperationException`.  
 The returned sorted set will be serializable if the specified sorted set is serializable.  
Type Parameters:  
`T` \- the class of the objects in the set  
Parameters:  
`s` \- the sorted set for which an unmodifiable view is to be returned.  
Returns:  
an unmodifiable view of the specified sorted set.  
* #### unmodifiableNavigableSet  
public static <T> [NavigableSet](../../java/util/NavigableSet.html "interface in java.util")<T> unmodifiableNavigableSet([NavigableSet](../../java/util/NavigableSet.html "interface in java.util")<T> s)  
Returns an unmodifiable view of the specified navigable set. This method allows modules to provide users with "read-only" access to internal navigable sets. Query operations on the returned navigable set "read through" to the specified navigable set. Attempts to modify the returned navigable set, whether direct, via its iterator, or via its`subSet`, `headSet`, or `tailSet` views, result in an `UnsupportedOperationException`.  
 The returned navigable set will be serializable if the specified navigable set is serializable.  
Type Parameters:  
`T` \- the class of the objects in the set  
Parameters:  
`s` \- the navigable set for which an unmodifiable view is to be returned  
Returns:  
an unmodifiable view of the specified navigable set  
Since:  
1.8  
* #### unmodifiableList  
public static <T> [List](../../java/util/List.html "interface in java.util")<T> unmodifiableList([List](../../java/util/List.html "interface in java.util")<? extends T> list)  
Returns an unmodifiable view of the specified list. This method allows modules to provide users with "read-only" access to internal lists. Query operations on the returned list "read through" to the specified list, and attempts to modify the returned list, whether direct or via its iterator, result in an`UnsupportedOperationException`.  
 The returned list will be serializable if the specified list is serializable. Similarly, the returned list will implement[RandomAccess](../../java/util/RandomAccess.html "interface in java.util") if the specified list does.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list for which an unmodifiable view is to be returned.  
Returns:  
an unmodifiable view of the specified list.  
* #### unmodifiableMap  
public static <K,V> [Map](../../java/util/Map.html "interface in java.util")<K,V> unmodifiableMap([Map](../../java/util/Map.html "interface in java.util")<? extends K,? extends V> m)  
Returns an unmodifiable view of the specified map. This method allows modules to provide users with "read-only" access to internal maps. Query operations on the returned map "read through" to the specified map, and attempts to modify the returned map, whether direct or via its collection views, result in an`UnsupportedOperationException`.  
 The returned map will be serializable if the specified map is serializable.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the map for which an unmodifiable view is to be returned.  
Returns:  
an unmodifiable view of the specified map.  
* #### unmodifiableSortedMap  
public static <K,V> [SortedMap](../../java/util/SortedMap.html "interface in java.util")<K,V> unmodifiableSortedMap([SortedMap](../../java/util/SortedMap.html "interface in java.util")<K,? extends V> m)  
Returns an unmodifiable view of the specified sorted map. This method allows modules to provide users with "read-only" access to internal sorted maps. Query operations on the returned sorted map "read through" to the specified sorted map. Attempts to modify the returned sorted map, whether direct, via its collection views, or via its`subMap`, `headMap`, or `tailMap` views, result in an `UnsupportedOperationException`.  
 The returned sorted map will be serializable if the specified sorted map is serializable.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the sorted map for which an unmodifiable view is to be returned.  
Returns:  
an unmodifiable view of the specified sorted map.  
* #### unmodifiableNavigableMap  
public static <K,V> [NavigableMap](../../java/util/NavigableMap.html "interface in java.util")<K,V> unmodifiableNavigableMap([NavigableMap](../../java/util/NavigableMap.html "interface in java.util")<K,? extends V> m)  
Returns an unmodifiable view of the specified navigable map. This method allows modules to provide users with "read-only" access to internal navigable maps. Query operations on the returned navigable map "read through" to the specified navigable map. Attempts to modify the returned navigable map, whether direct, via its collection views, or via its`subMap`, `headMap`, or `tailMap` views, result in an `UnsupportedOperationException`.  
 The returned navigable map will be serializable if the specified navigable map is serializable.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the navigable map for which an unmodifiable view is to be returned  
Returns:  
an unmodifiable view of the specified navigable map  
Since:  
1.8  
* #### synchronizedCollection  
public static <T> [Collection](../../java/util/Collection.html "interface in java.util")<T> synchronizedCollection([Collection](../../java/util/Collection.html "interface in java.util")<T> c)  
Returns a synchronized (thread-safe) collection backed by the specified collection. In order to guarantee serial access, it is critical that**all** access to the backing collection is accomplished through the returned collection.  
 It is imperative that the user manually synchronize on the returned collection when traversing it via [Iterator](../../java/util/Iterator.html "interface in java.util"), [Spliterator](../../java/util/Spliterator.html "interface in java.util") or [Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  Collection c = Collections.synchronizedCollection(myCollection);  
     ...  
  synchronized (c) {  
      Iterator i = c.iterator(); // Must be in the synchronized block  
      while (i.hasNext())  
         foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned collection does _not_ pass the `hashCode` and `equals` operations through to the backing collection, but relies on `Object`'s equals and hashCode methods. This is necessary to preserve the contracts of these operations in the case that the backing collection is a set or a list.  
 The returned collection will be serializable if the specified collection is serializable.  
Type Parameters:  
`T` \- the class of the objects in the collection  
Parameters:  
`c` \- the collection to be "wrapped" in a synchronized collection.  
Returns:  
a synchronized view of the specified collection.  
* #### synchronizedSet  
public static <T> [Set](../../java/util/Set.html "interface in java.util")<T> synchronizedSet([Set](../../java/util/Set.html "interface in java.util")<T> s)  
Returns a synchronized (thread-safe) set backed by the specified set. In order to guarantee serial access, it is critical that**all** access to the backing set is accomplished through the returned set.  
 It is imperative that the user manually synchronize on the returned collection when traversing it via [Iterator](../../java/util/Iterator.html "interface in java.util"), [Spliterator](../../java/util/Spliterator.html "interface in java.util") or [Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  Set s = Collections.synchronizedSet(new HashSet());  
      ...  
  synchronized (s) {  
      Iterator i = s.iterator(); // Must be in the synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned set will be serializable if the specified set is serializable.  
Type Parameters:  
`T` \- the class of the objects in the set  
Parameters:  
`s` \- the set to be "wrapped" in a synchronized set.  
Returns:  
a synchronized view of the specified set.  
* #### synchronizedSortedSet  
public static <T> [SortedSet](../../java/util/SortedSet.html "interface in java.util")<T> synchronizedSortedSet([SortedSet](../../java/util/SortedSet.html "interface in java.util")<T> s)  
Returns a synchronized (thread-safe) sorted set backed by the specified sorted set. In order to guarantee serial access, it is critical that**all** access to the backing sorted set is accomplished through the returned sorted set (or its views).  
 It is imperative that the user manually synchronize on the returned sorted set when traversing it or any of its `subSet`,`headSet`, or `tailSet` views via [Iterator](../../java/util/Iterator.html "interface in java.util"),[Spliterator](../../java/util/Spliterator.html "interface in java.util") or [Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());  
      ...  
  synchronized (s) {  
      Iterator i = s.iterator(); // Must be in the synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 or:  
  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());  
  SortedSet s2 = s.headSet(foo);  
      ...  
  synchronized (s) {  // Note: s, not s2!!!  
      Iterator i = s2.iterator(); // Must be in the synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned sorted set will be serializable if the specified sorted set is serializable.  
Type Parameters:  
`T` \- the class of the objects in the set  
Parameters:  
`s` \- the sorted set to be "wrapped" in a synchronized sorted set.  
Returns:  
a synchronized view of the specified sorted set.  
* #### synchronizedNavigableSet  
public static <T> [NavigableSet](../../java/util/NavigableSet.html "interface in java.util")<T> synchronizedNavigableSet([NavigableSet](../../java/util/NavigableSet.html "interface in java.util")<T> s)  
Returns a synchronized (thread-safe) navigable set backed by the specified navigable set. In order to guarantee serial access, it is critical that **all** access to the backing navigable set is accomplished through the returned navigable set (or its views).  
 It is imperative that the user manually synchronize on the returned navigable set when traversing it, or any of its `subSet`,`headSet`, or `tailSet` views, via [Iterator](../../java/util/Iterator.html "interface in java.util"),[Spliterator](../../java/util/Spliterator.html "interface in java.util") or [Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());  
      ...  
  synchronized (s) {  
      Iterator i = s.iterator(); // Must be in the synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 or:  
  NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());  
  NavigableSet s2 = s.headSet(foo, true);  
      ...  
  synchronized (s) {  // Note: s, not s2!!!  
      Iterator i = s2.iterator(); // Must be in the synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned navigable set will be serializable if the specified navigable set is serializable.  
Type Parameters:  
`T` \- the class of the objects in the set  
Parameters:  
`s` \- the navigable set to be "wrapped" in a synchronized navigable set  
Returns:  
a synchronized view of the specified navigable set  
Since:  
1.8  
* #### synchronizedList  
public static <T> [List](../../java/util/List.html "interface in java.util")<T> synchronizedList([List](../../java/util/List.html "interface in java.util")<T> list)  
Returns a synchronized (thread-safe) list backed by the specified list. In order to guarantee serial access, it is critical that**all** access to the backing list is accomplished through the returned list.  
 It is imperative that the user manually synchronize on the returned list when traversing it via [Iterator](../../java/util/Iterator.html "interface in java.util"), [Spliterator](../../java/util/Spliterator.html "interface in java.util") or [Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  List list = Collections.synchronizedList(new ArrayList());  
      ...  
  synchronized (list) {  
      Iterator i = list.iterator(); // Must be in synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned list will be serializable if the specified list is serializable.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`list` \- the list to be "wrapped" in a synchronized list.  
Returns:  
a synchronized view of the specified list.  
* #### synchronizedMap  
public static <K,V> [Map](../../java/util/Map.html "interface in java.util")<K,V> synchronizedMap([Map](../../java/util/Map.html "interface in java.util")<K,V> m)  
Returns a synchronized (thread-safe) map backed by the specified map. In order to guarantee serial access, it is critical that**all** access to the backing map is accomplished through the returned map.  
 It is imperative that the user manually synchronize on the returned map when traversing any of its collection views via [Iterator](../../java/util/Iterator.html "interface in java.util"),[Spliterator](../../java/util/Spliterator.html "interface in java.util") or [Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  Map m = Collections.synchronizedMap(new HashMap());  
      ...  
  Set s = m.keySet();  // Needn't be in synchronized block  
      ...  
  synchronized (m) {  // Synchronizing on m, not s!  
      Iterator i = s.iterator(); // Must be in synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned map will be serializable if the specified map is serializable.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the map to be "wrapped" in a synchronized map.  
Returns:  
a synchronized view of the specified map.  
* #### synchronizedSortedMap  
public static <K,V> [SortedMap](../../java/util/SortedMap.html "interface in java.util")<K,V> synchronizedSortedMap([SortedMap](../../java/util/SortedMap.html "interface in java.util")<K,V> m)  
Returns a synchronized (thread-safe) sorted map backed by the specified sorted map. In order to guarantee serial access, it is critical that**all** access to the backing sorted map is accomplished through the returned sorted map (or its views).  
 It is imperative that the user manually synchronize on the returned sorted map when traversing any of its collection views, or the collections views of any of its `subMap`, `headMap` or`tailMap` views, via [Iterator](../../java/util/Iterator.html "interface in java.util"), [Spliterator](../../java/util/Spliterator.html "interface in java.util") or[Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());  
      ...  
  Set s = m.keySet();  // Needn't be in synchronized block  
      ...  
  synchronized (m) {  // Synchronizing on m, not s!  
      Iterator i = s.iterator(); // Must be in synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 or:  
  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());  
  SortedMap m2 = m.subMap(foo, bar);  
      ...  
  Set s2 = m2.keySet();  // Needn't be in synchronized block  
      ...  
  synchronized (m) {  // Synchronizing on m, not m2 or s2!  
      Iterator i = s2.iterator(); // Must be in synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned sorted map will be serializable if the specified sorted map is serializable.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the sorted map to be "wrapped" in a synchronized sorted map.  
Returns:  
a synchronized view of the specified sorted map.  
* #### synchronizedNavigableMap  
public static <K,V> [NavigableMap](../../java/util/NavigableMap.html "interface in java.util")<K,V> synchronizedNavigableMap([NavigableMap](../../java/util/NavigableMap.html "interface in java.util")<K,V> m)  
Returns a synchronized (thread-safe) navigable map backed by the specified navigable map. In order to guarantee serial access, it is critical that **all** access to the backing navigable map is accomplished through the returned navigable map (or its views).  
 It is imperative that the user manually synchronize on the returned navigable map when traversing any of its collection views, or the collections views of any of its `subMap`, `headMap` or`tailMap` views, via [Iterator](../../java/util/Iterator.html "interface in java.util"), [Spliterator](../../java/util/Spliterator.html "interface in java.util") or[Stream](../../java/util/stream/Stream.html "interface in java.util.stream"):  
  NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap());  
      ...  
  Set s = m.keySet();  // Needn't be in synchronized block  
      ...  
  synchronized (m) {  // Synchronizing on m, not s!  
      Iterator i = s.iterator(); // Must be in synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 or:  
  NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap());  
  NavigableMap m2 = m.subMap(foo, true, bar, false);  
      ...  
  Set s2 = m2.keySet();  // Needn't be in synchronized block  
      ...  
  synchronized (m) {  // Synchronizing on m, not m2 or s2!  
      Iterator i = s.iterator(); // Must be in synchronized block  
      while (i.hasNext())  
          foo(i.next());  
  }  
       
 Failure to follow this advice may result in non-deterministic behavior.  
The returned navigable map will be serializable if the specified navigable map is serializable.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the navigable map to be "wrapped" in a synchronized navigable map  
Returns:  
a synchronized view of the specified navigable map.  
Since:  
1.8  
* #### checkedCollection  
public static <E> [Collection](../../java/util/Collection.html "interface in java.util")<E> checkedCollection([Collection](../../java/util/Collection.html "interface in java.util")<E> c,  
                                                  [Class](../../java/lang/Class.html "class in java.lang")<E> type)  
Returns a dynamically typesafe view of the specified collection. Any attempt to insert an element of the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Assuming a collection contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the collection takes place through the view, it is_guaranteed_ that the collection cannot contain an incorrectly typed element.  
The generics mechanism in the language provides compile-time (static) type checking, but it is possible to defeat this mechanism with unchecked casts. Usually this is not a problem, as the compiler issues warnings on all such unchecked operations. There are, however, times when static type checking alone is not sufficient. For example, suppose a collection is passed to a third-party library and it is imperative that the library code not corrupt the collection by inserting an element of the wrong type.  
Another use of dynamically typesafe views is debugging. Suppose a program fails with a `ClassCastException`, indicating that an incorrectly typed element was put into a parameterized collection. Unfortunately, the exception can occur at any time after the erroneous element is inserted, so it typically provides little or no information as to the real source of the problem. If the problem is reproducible, one can quickly determine its source by temporarily modifying the program to wrap the collection with a dynamically typesafe view. For example, this declaration:  
 `  
     Collection<String> c = new HashSet<>();  
 `  
 may be replaced temporarily by this one:  
 `  
     Collection<String> c = Collections.checkedCollection(  
         new HashSet<>(), String.class);  
 `  
 Running the program again will cause it to fail at the point where an incorrectly typed element is inserted into the collection, clearly identifying the source of the problem. Once the problem is fixed, the modified declaration may be reverted back to the original.  
The returned collection does _not_ pass the hashCode and equals operations through to the backing collection, but relies on`Object`'s `equals` and `hashCode` methods. This is necessary to preserve the contracts of these operations in the case that the backing collection is a set or a list.  
The returned collection will be serializable if the specified collection is serializable.  
Since `null` is considered to be a value of any reference type, the returned collection permits insertion of null elements whenever the backing collection does.  
Type Parameters:  
`E` \- the class of the objects in the collection  
Parameters:  
`c` \- the collection for which a dynamically typesafe view is to be returned  
`type` \- the type of element that `c` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified collection  
Since:  
1.5  
* #### checkedQueue  
public static <E> [Queue](../../java/util/Queue.html "interface in java.util")<E> checkedQueue([Queue](../../java/util/Queue.html "interface in java.util")<E> queue,  
                                        [Class](../../java/lang/Class.html "class in java.lang")<E> type)  
Returns a dynamically typesafe view of the specified queue. Any attempt to insert an element of the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Assuming a queue contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the queue takes place through the view, it is _guaranteed_ that the queue cannot contain an incorrectly typed element.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned queue will be serializable if the specified queue is serializable.  
Since `null` is considered to be a value of any reference type, the returned queue permits insertion of `null` elements whenever the backing queue does.  
Type Parameters:  
`E` \- the class of the objects in the queue  
Parameters:  
`queue` \- the queue for which a dynamically typesafe view is to be returned  
`type` \- the type of element that `queue` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified queue  
Since:  
1.8  
* #### checkedSet  
public static <E> [Set](../../java/util/Set.html "interface in java.util")<E> checkedSet([Set](../../java/util/Set.html "interface in java.util")<E> s,  
                                    [Class](../../java/lang/Class.html "class in java.lang")<E> type)  
Returns a dynamically typesafe view of the specified set. Any attempt to insert an element of the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Assuming a set contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the set takes place through the view, it is _guaranteed_ that the set cannot contain an incorrectly typed element.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned set will be serializable if the specified set is serializable.  
Since `null` is considered to be a value of any reference type, the returned set permits insertion of null elements whenever the backing set does.  
Type Parameters:  
`E` \- the class of the objects in the set  
Parameters:  
`s` \- the set for which a dynamically typesafe view is to be returned  
`type` \- the type of element that `s` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified set  
Since:  
1.5  
* #### checkedSortedSet  
public static <E> [SortedSet](../../java/util/SortedSet.html "interface in java.util")<E> checkedSortedSet([SortedSet](../../java/util/SortedSet.html "interface in java.util")<E> s,  
                                                [Class](../../java/lang/Class.html "class in java.lang")<E> type)  
Returns a dynamically typesafe view of the specified sorted set. Any attempt to insert an element of the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Assuming a sorted set contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the sorted set takes place through the view, it is_guaranteed_ that the sorted set cannot contain an incorrectly typed element.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned sorted set will be serializable if the specified sorted set is serializable.  
Since `null` is considered to be a value of any reference type, the returned sorted set permits insertion of null elements whenever the backing sorted set does.  
Type Parameters:  
`E` \- the class of the objects in the set  
Parameters:  
`s` \- the sorted set for which a dynamically typesafe view is to be returned  
`type` \- the type of element that `s` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified sorted set  
Since:  
1.5  
* #### checkedNavigableSet  
public static <E> [NavigableSet](../../java/util/NavigableSet.html "interface in java.util")<E> checkedNavigableSet([NavigableSet](../../java/util/NavigableSet.html "interface in java.util")<E> s,  
                                                      [Class](../../java/lang/Class.html "class in java.lang")<E> type)  
Returns a dynamically typesafe view of the specified navigable set. Any attempt to insert an element of the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Assuming a navigable set contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the navigable set takes place through the view, it is_guaranteed_ that the navigable set cannot contain an incorrectly typed element.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned navigable set will be serializable if the specified navigable set is serializable.  
Since `null` is considered to be a value of any reference type, the returned navigable set permits insertion of null elements whenever the backing sorted set does.  
Type Parameters:  
`E` \- the class of the objects in the set  
Parameters:  
`s` \- the navigable set for which a dynamically typesafe view is to be returned  
`type` \- the type of element that `s` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified navigable set  
Since:  
1.8  
* #### checkedList  
public static <E> [List](../../java/util/List.html "interface in java.util")<E> checkedList([List](../../java/util/List.html "interface in java.util")<E> list,  
                                      [Class](../../java/lang/Class.html "class in java.lang")<E> type)  
Returns a dynamically typesafe view of the specified list. Any attempt to insert an element of the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Assuming a list contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the list takes place through the view, it is _guaranteed_ that the list cannot contain an incorrectly typed element.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned list will be serializable if the specified list is serializable.  
Since `null` is considered to be a value of any reference type, the returned list permits insertion of null elements whenever the backing list does.  
Type Parameters:  
`E` \- the class of the objects in the list  
Parameters:  
`list` \- the list for which a dynamically typesafe view is to be returned  
`type` \- the type of element that `list` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified list  
Since:  
1.5  
* #### checkedMap  
public static <K,V> [Map](../../java/util/Map.html "interface in java.util")<K,V> checkedMap([Map](../../java/util/Map.html "interface in java.util")<K,V> m,  
                                        [Class](../../java/lang/Class.html "class in java.lang")<K> keyType,  
                                        [Class](../../java/lang/Class.html "class in java.lang")<V> valueType)  
Returns a dynamically typesafe view of the specified map. Any attempt to insert a mapping whose key or value have the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Similarly, any attempt to modify the value currently associated with a key will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"), whether the modification is attempted directly through the map itself, or through a [Map.Entry](../../java/util/Map.Entry.html "interface in java.util") instance obtained from the map's [entry set](../../java/util/Map.html#entrySet--) view.  
Assuming a map contains no incorrectly typed keys or values prior to the time a dynamically typesafe view is generated, and that all subsequent access to the map takes place through the view (or one of its collection views), it is _guaranteed_ that the map cannot contain an incorrectly typed key or value.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned map will be serializable if the specified map is serializable.  
Since `null` is considered to be a value of any reference type, the returned map permits insertion of null keys or values whenever the backing map does.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the map for which a dynamically typesafe view is to be returned  
`keyType` \- the type of key that `m` is permitted to hold  
`valueType` \- the type of value that `m` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified map  
Since:  
1.5  
* #### checkedSortedMap  
public static <K,V> [SortedMap](../../java/util/SortedMap.html "interface in java.util")<K,V> checkedSortedMap([SortedMap](../../java/util/SortedMap.html "interface in java.util")<K,V> m,  
                                                    [Class](../../java/lang/Class.html "class in java.lang")<K> keyType,  
                                                    [Class](../../java/lang/Class.html "class in java.lang")<V> valueType)  
Returns a dynamically typesafe view of the specified sorted map. Any attempt to insert a mapping whose key or value have the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Similarly, any attempt to modify the value currently associated with a key will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"), whether the modification is attempted directly through the map itself, or through a [Map.Entry](../../java/util/Map.Entry.html "interface in java.util") instance obtained from the map's [entry set](../../java/util/Map.html#entrySet--) view.  
Assuming a map contains no incorrectly typed keys or values prior to the time a dynamically typesafe view is generated, and that all subsequent access to the map takes place through the view (or one of its collection views), it is _guaranteed_ that the map cannot contain an incorrectly typed key or value.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned map will be serializable if the specified map is serializable.  
Since `null` is considered to be a value of any reference type, the returned map permits insertion of null keys or values whenever the backing map does.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`m` \- the map for which a dynamically typesafe view is to be returned  
`keyType` \- the type of key that `m` is permitted to hold  
`valueType` \- the type of value that `m` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified map  
Since:  
1.5  
* #### checkedNavigableMap  
public static <K,V> [NavigableMap](../../java/util/NavigableMap.html "interface in java.util")<K,V> checkedNavigableMap([NavigableMap](../../java/util/NavigableMap.html "interface in java.util")<K,V> m,  
                                                          [Class](../../java/lang/Class.html "class in java.lang")<K> keyType,  
                                                          [Class](../../java/lang/Class.html "class in java.lang")<V> valueType)  
Returns a dynamically typesafe view of the specified navigable map. Any attempt to insert a mapping whose key or value have the wrong type will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"). Similarly, any attempt to modify the value currently associated with a key will result in an immediate [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang"), whether the modification is attempted directly through the map itself, or through a [Map.Entry](../../java/util/Map.Entry.html "interface in java.util") instance obtained from the map's [entry set](../../java/util/Map.html#entrySet--) view.  
Assuming a map contains no incorrectly typed keys or values prior to the time a dynamically typesafe view is generated, and that all subsequent access to the map takes place through the view (or one of its collection views), it is _guaranteed_ that the map cannot contain an incorrectly typed key or value.  
A discussion of the use of dynamically typesafe views may be found in the documentation for the [checkedCollection](../../java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-) method.  
The returned map will be serializable if the specified map is serializable.  
Since `null` is considered to be a value of any reference type, the returned map permits insertion of null keys or values whenever the backing map does.  
Type Parameters:  
`K` \- type of map keys  
`V` \- type of map values  
Parameters:  
`m` \- the map for which a dynamically typesafe view is to be returned  
`keyType` \- the type of key that `m` is permitted to hold  
`valueType` \- the type of value that `m` is permitted to hold  
Returns:  
a dynamically typesafe view of the specified map  
Since:  
1.8  
* #### emptyIterator  
public static <T> [Iterator](../../java/util/Iterator.html "interface in java.util")<T> emptyIterator()  
Type Parameters:  
`T` \- type of elements, if there were any, in the iterator  
Returns:  
an empty iterator  
Since:  
1.7  
* #### emptyListIterator  
public static <T> [ListIterator](../../java/util/ListIterator.html "interface in java.util")<T> emptyListIterator()  
Type Parameters:  
`T` \- type of elements, if there were any, in the iterator  
Returns:  
an empty list iterator  
Since:  
1.7  
* #### emptyEnumeration  
public static <T> [Enumeration](../../java/util/Enumeration.html "interface in java.util")<T> emptyEnumeration()  
Returns an enumeration that has no elements. More precisely,  
         * [hasMoreElements](../../java/util/Enumeration.html#hasMoreElements--) always returns `false`.  
         * [nextElement](../../java/util/Enumeration.html#nextElement--) always throws[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util").  
Implementations of this method are permitted, but not required, to return the same object from multiple invocations.  
Type Parameters:  
`T` \- the class of the objects in the enumeration  
Returns:  
an empty enumeration  
Since:  
1.7  
* #### emptySet  
public static final <T> [Set](../../java/util/Set.html "interface in java.util")<T> emptySet()  
Returns an empty set (immutable). This set is serializable. Unlike the like-named field, this method is parameterized.  
This example illustrates the type-safe way to obtain an empty set:  
     Set<String> s = Collections.emptySet();  
       
Implementation Note:  
Implementations of this method need not create a separate`Set` object for each call. Using this method is likely to have comparable cost to using the like-named field. (Unlike this method, the field does not provide type safety.)  
Type Parameters:  
`T` \- the class of the objects in the set  
Returns:  
the empty set  
Since:  
1.5  
See Also:  
[EMPTY\_SET](../../java/util/Collections.html#EMPTY%5FSET)  
* #### emptySortedSet  
public static <E> [SortedSet](../../java/util/SortedSet.html "interface in java.util")<E> emptySortedSet()  
Returns an empty sorted set (immutable). This set is serializable.  
This example illustrates the type-safe way to obtain an empty sorted set:  
 `  
     SortedSet<String> s = Collections.emptySortedSet();  
 `  
Implementation Note:  
Implementations of this method need not create a separate`SortedSet` object for each call.  
Type Parameters:  
`E` \- type of elements, if there were any, in the set  
Returns:  
the empty sorted set  
Since:  
1.8  
* #### emptyNavigableSet  
public static <E> [NavigableSet](../../java/util/NavigableSet.html "interface in java.util")<E> emptyNavigableSet()  
Returns an empty navigable set (immutable). This set is serializable.  
This example illustrates the type-safe way to obtain an empty navigable set:  
 `  
     NavigableSet<String> s = Collections.emptyNavigableSet();  
 `  
Implementation Note:  
Implementations of this method need not create a separate `NavigableSet` object for each call.  
Type Parameters:  
`E` \- type of elements, if there were any, in the set  
Returns:  
the empty navigable set  
Since:  
1.8  
* #### emptyList  
public static final <T> [List](../../java/util/List.html "interface in java.util")<T> emptyList()  
Returns an empty list (immutable). This list is serializable.  
This example illustrates the type-safe way to obtain an empty list:  
     List<String> s = Collections.emptyList();  
       
Implementation Note:  
Implementations of this method need not create a separate `List` object for each call. Using this method is likely to have comparable cost to using the like-named field. (Unlike this method, the field does not provide type safety.)  
Type Parameters:  
`T` \- type of elements, if there were any, in the list  
Returns:  
an empty immutable list  
Since:  
1.5  
See Also:  
[EMPTY\_LIST](../../java/util/Collections.html#EMPTY%5FLIST)  
* #### emptyMap  
public static final <K,V> [Map](../../java/util/Map.html "interface in java.util")<K,V> emptyMap()  
Returns an empty map (immutable). This map is serializable.  
This example illustrates the type-safe way to obtain an empty map:  
     Map<String, Date> s = Collections.emptyMap();  
       
Implementation Note:  
Implementations of this method need not create a separate`Map` object for each call. Using this method is likely to have comparable cost to using the like-named field. (Unlike this method, the field does not provide type safety.)  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Returns:  
an empty map  
Since:  
1.5  
See Also:  
[EMPTY\_MAP](../../java/util/Collections.html#EMPTY%5FMAP)  
* #### emptySortedMap  
public static final <K,V> [SortedMap](../../java/util/SortedMap.html "interface in java.util")<K,V> emptySortedMap()  
Returns an empty sorted map (immutable). This map is serializable.  
This example illustrates the type-safe way to obtain an empty map:  
 `  
     SortedMap<String, Date> s = Collections.emptySortedMap();  
 `  
Implementation Note:  
Implementations of this method need not create a separate`SortedMap` object for each call.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Returns:  
an empty sorted map  
Since:  
1.8  
* #### emptyNavigableMap  
public static final <K,V> [NavigableMap](../../java/util/NavigableMap.html "interface in java.util")<K,V> emptyNavigableMap()  
Returns an empty navigable map (immutable). This map is serializable.  
This example illustrates the type-safe way to obtain an empty map:  
 `  
     NavigableMap<String, Date> s = Collections.emptyNavigableMap();  
 `  
Implementation Note:  
Implementations of this method need not create a separate`NavigableMap` object for each call.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Returns:  
an empty navigable map  
Since:  
1.8  
* #### singleton  
public static <T> [Set](../../java/util/Set.html "interface in java.util")<T> singleton(T o)  
Returns an immutable set containing only the specified object. The returned set is serializable.  
Type Parameters:  
`T` \- the class of the objects in the set  
Parameters:  
`o` \- the sole object to be stored in the returned set.  
Returns:  
an immutable set containing only the specified object.  
* #### singletonList  
public static <T> [List](../../java/util/List.html "interface in java.util")<T> singletonList(T o)  
Returns an immutable list containing only the specified object. The returned list is serializable.  
Type Parameters:  
`T` \- the class of the objects in the list  
Parameters:  
`o` \- the sole object to be stored in the returned list.  
Returns:  
an immutable list containing only the specified object.  
Since:  
1.3  
* #### singletonMap  
public static <K,V> [Map](../../java/util/Map.html "interface in java.util")<K,V> singletonMap(K key,  
                                          V value)  
Returns an immutable map, mapping only the specified key to the specified value. The returned map is serializable.  
Type Parameters:  
`K` \- the class of the map keys  
`V` \- the class of the map values  
Parameters:  
`key` \- the sole key to be stored in the returned map.  
`value` \- the value to which the returned map maps `key`.  
Returns:  
an immutable map containing only the specified key-value mapping.  
Since:  
1.3  
* #### nCopies  
public static <T> [List](../../java/util/List.html "interface in java.util")<T> nCopies(int n,  
                                  T o)  
Returns an immutable list consisting of `n` copies of the specified object. The newly allocated data object is tiny (it contains a single reference to the data object). This method is useful in combination with the `List.addAll` method to grow lists. The returned list is serializable.  
Type Parameters:  
`T` \- the class of the object to copy and of the objects in the returned list.  
Parameters:  
`n` \- the number of elements in the returned list.  
`o` \- the element to appear repeatedly in the returned list.  
Returns:  
an immutable list consisting of `n` copies of the specified object.  
Throws:  
`[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if `n < 0`  
See Also:  
[List.addAll(Collection)](../../java/util/List.html#addAll-java.util.Collection-), [List.addAll(int, Collection)](../../java/util/List.html#addAll-int-java.util.Collection-)  
* #### reverseOrder  
public static <T> [Comparator](../../java/util/Comparator.html "interface in java.util")<T> reverseOrder()  
Returns a comparator that imposes the reverse of the _natural ordering_ on a collection of objects that implement the`Comparable` interface. (The natural ordering is the ordering imposed by the objects' own `compareTo` method.) This enables a simple idiom for sorting (or maintaining) collections (or arrays) of objects that implement the `Comparable` interface in reverse-natural-order. For example, suppose `a` is an array of strings. Then:  
          Arrays.sort(a, Collections.reverseOrder());  
       
 sorts the array in reverse-lexicographic (alphabetical) order.  
 The returned comparator is serializable.  
Type Parameters:  
`T` \- the class of the objects compared by the comparator  
Returns:  
A comparator that imposes the reverse of the _natural ordering_ on a collection of objects that implement the `Comparable` interface.  
See Also:  
[Comparable](../../java/lang/Comparable.html "interface in java.lang")  
* #### reverseOrder  
public static <T> [Comparator](../../java/util/Comparator.html "interface in java.util")<T> reverseOrder([Comparator](../../java/util/Comparator.html "interface in java.util")<T> cmp)  
Returns a comparator that imposes the reverse ordering of the specified comparator. If the specified comparator is `null`, this method is equivalent to [reverseOrder()](../../java/util/Collections.html#reverseOrder--) (in other words, it returns a comparator that imposes the reverse of the _natural ordering_ on a collection of objects that implement the Comparable interface).  
The returned comparator is serializable (assuming the specified comparator is also serializable or `null`).  
Type Parameters:  
`T` \- the class of the objects compared by the comparator  
Parameters:  
`cmp` \- a comparator who's ordering is to be reversed by the returned comparator or `null`  
Returns:  
A comparator that imposes the reverse ordering of the specified comparator.  
Since:  
1.5  
* #### enumeration  
public static <T> [Enumeration](../../java/util/Enumeration.html "interface in java.util")<T> enumeration([Collection](../../java/util/Collection.html "interface in java.util")<T> c)  
Returns an enumeration over the specified collection. This provides interoperability with legacy APIs that require an enumeration as input.  
The iterator returned from a call to [Enumeration.asIterator()](../../java/util/Enumeration.html#asIterator--) does not support removal of elements from the specified collection. This is necessary to avoid unintentionally increasing the capabilities of the returned enumeration.  
Type Parameters:  
`T` \- the class of the objects in the collection  
Parameters:  
`c` \- the collection for which an enumeration is to be returned.  
Returns:  
an enumeration over the specified collection.  
See Also:  
[Enumeration](../../java/util/Enumeration.html "interface in java.util")  
* #### list  
public static <T> [ArrayList](../../java/util/ArrayList.html "class in java.util")<T> list([Enumeration](../../java/util/Enumeration.html "interface in java.util")<T> e)  
Returns an array list containing the elements returned by the specified enumeration in the order they are returned by the enumeration. This method provides interoperability between legacy APIs that return enumerations and new APIs that require collections.  
Type Parameters:  
`T` \- the class of the objects returned by the enumeration  
Parameters:  
`e` \- enumeration providing elements for the returned array list  
Returns:  
an array list containing the elements returned by the specified enumeration.  
Since:  
1.4  
See Also:  
[Enumeration](../../java/util/Enumeration.html "interface in java.util"), [ArrayList](../../java/util/ArrayList.html "class in java.util")  
* #### frequency  
public static int frequency([Collection](../../java/util/Collection.html "interface in java.util")<?> c,  
                            [Object](../../java/lang/Object.html "class in java.lang") o)  
Returns the number of elements in the specified collection equal to the specified object. More formally, returns the number of elements`e` in the collection such that`Objects.equals(o, e)`.  
Parameters:  
`c` \- the collection in which to determine the frequency of `o`  
`o` \- the object whose frequency is to be determined  
Returns:  
the number of elements in `c` equal to `o`  
Throws:  
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if `c` is null  
Since:  
1.5  
* #### disjoint  
public static boolean disjoint([Collection](../../java/util/Collection.html "interface in java.util")<?> c1,  
                               [Collection](../../java/util/Collection.html "interface in java.util")<?> c2)  
Returns `true` if the two specified collections have no elements in common.  
Care must be exercised if this method is used on collections that do not comply with the general contract for `Collection`. Implementations may elect to iterate over either collection and test for containment in the other collection (or to perform any equivalent computation). If either collection uses a nonstandard equality test (as does a [SortedSet](../../java/util/SortedSet.html "interface in java.util") whose ordering is not _compatible with equals_, or the key set of an [IdentityHashMap](../../java/util/IdentityHashMap.html "class in java.util")), both collections must use the same nonstandard equality test, or the result of this method is undefined.  
Care must also be exercised when using collections that have restrictions on the elements that they may contain. Collection implementations are allowed to throw exceptions for any operation involving elements they deem ineligible. For absolute safety the specified collections should contain only elements which are eligible elements for both collections.  
Note that it is permissible to pass the same collection in both parameters, in which case the method will return `true` if and only if the collection is empty.  
Parameters:  
`c1` \- a collection  
`c2` \- a collection  
Returns:  
`true` if the two specified collections have no elements in common.  
Throws:  
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if either collection is `null`.  
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if one collection contains a `null` element and `null` is not an eligible element for the other collection. ([optional](Collection.html#optional-restrictions))  
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if one collection contains an element that is of a type which is ineligible for the other collection. ([optional](Collection.html#optional-restrictions))  
Since:  
1.5  
* #### addAll  
[@SafeVarargs](../../java/lang/SafeVarargs.html "annotation in java.lang")  
public static <T> boolean addAll([Collection](../../java/util/Collection.html "interface in java.util")<? super T> c,  
                                 T... elements)  
Adds all of the specified elements to the specified collection. Elements to be added may be specified individually or as an array. The behavior of this convenience method is identical to that of`c.addAll(Arrays.asList(elements))`, but this method is likely to run significantly faster under most implementations.  
When elements are specified individually, this method provides a convenient way to add a few elements to an existing collection:  
     Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");  
       
Type Parameters:  
`T` \- the class of the elements to add and of the collection  
Parameters:  
`c` \- the collection into which `elements` are to be inserted  
`elements` \- the elements to insert into `c`  
Returns:  
`true` if the collection changed as a result of the call  
Throws:  
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if `c` does not support the `add` operation  
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if `elements` contains one or more null values and `c` does not permit null elements, or if `c` or `elements` are `null`  
`[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if some property of a value in`elements` prevents it from being added to `c`  
Since:  
1.5  
See Also:  
[Collection.addAll(Collection)](../../java/util/Collection.html#addAll-java.util.Collection-)  
* #### newSetFromMap  
public static <E> [Set](../../java/util/Set.html "interface in java.util")<E> newSetFromMap([Map](../../java/util/Map.html "interface in java.util")<E,[Boolean](../../java/lang/Boolean.html "class in java.lang")> map)  
Returns a set backed by the specified map. The resulting set displays the same ordering, concurrency, and performance characteristics as the backing map. In essence, this factory method provides a [Set](../../java/util/Set.html "interface in java.util") implementation corresponding to any [Map](../../java/util/Map.html "interface in java.util") implementation. There is no need to use this method on a [Map](../../java/util/Map.html "interface in java.util") implementation that already has a corresponding [Set](../../java/util/Set.html "interface in java.util") implementation (such as [HashMap](../../java/util/HashMap.html "class in java.util") or [TreeMap](../../java/util/TreeMap.html "class in java.util")).  
Each method invocation on the set returned by this method results in exactly one method invocation on the backing map or its `keySet` view, with one exception. The `addAll` method is implemented as a sequence of `put` invocations on the backing map.  
The specified map must be empty at the time this method is invoked, and should not be accessed directly after this method returns. These conditions are ensured if the map is created empty, passed directly to this method, and no reference to the map is retained, as illustrated in the following code fragment:  
    Set<Object> weakHashSet = Collections.newSetFromMap(  
        new WeakHashMap<Object, Boolean>());  
       
Type Parameters:  
`E` \- the class of the map keys and of the objects in the returned set  
Parameters:  
`map` \- the backing map  
Returns:  
the set backed by the map  
Throws:  
`[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if `map` is not empty  
Since:  
1.6  
* #### asLifoQueue  
public static <T> [Queue](../../java/util/Queue.html "interface in java.util")<T> asLifoQueue([Deque](../../java/util/Deque.html "interface in java.util")<T> deque)  
Returns a view of a [Deque](../../java/util/Deque.html "interface in java.util") as a Last-in-first-out (Lifo)[Queue](../../java/util/Queue.html "interface in java.util"). Method `add` is mapped to `push`,`remove` is mapped to `pop` and so on. This view can be useful when you would like to use a method requiring a `Queue` but you need Lifo ordering.  
Each method invocation on the queue returned by this method results in exactly one method invocation on the backing deque, with one exception. The [addAll](../../java/util/Collection.html#addAll-java.util.Collection-) method is implemented as a sequence of [addFirst](../../java/util/Deque.html#addFirst-E-) invocations on the backing deque.  
Type Parameters:  
`T` \- the class of the objects in the deque  
Parameters:  
`deque` \- the deque  
Returns:  
the queue  
Since:  
1.6

Collections (Java SE 9 & JDK 9 ) (original) (raw)

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