java.util
Class Collections

java.lang.Object   
  java.util.Collections

public class Collections
extends Object   

This class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, "wrappers", which return a new collection backed by a specified collection, and a few other odds and ends.

The methods of this class all throw a NullPointerException if the collections or class objects provided to them are null.

The documentation for the polymorphic algorithms contained in this class generally includes a brief description of the implementation. Such descriptions should be regarded as implementation notes, rather than parts of the specification. Implementors should feel free to substitute other algorithms, so long as the specification itself is adhered to. (For example, the algorithm used by sort does not have to be a mergesort, but it does have to be stable.)

The "destructive" algorithms contained in this class, that is, the algorithms that modify the collection on which they operate, are specified to throw UnsupportedOperationException if the collection does not support the appropriate mutation primitive(s), such as the set method. These algorithms may, but are not required to, throw this exception if an invocation would have no effect on the collection. For example, invoking the sort method on an unmodifiable list that is already sorted may or may not throw UnsupportedOperationException.

This class is a member of the Java Collections Framework.

Since:

1.2

See Also:

Collection , Set , List , Map

Field Summary

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

static <T> boolean	addAll (Collection <? super T> c, T... a) Adds all of the specified elements to the specified collection.
static <T> int	binarySearch (List <? extends Comparable <? super T>> list, T key) Searches the specified list for the specified object using the binary search algorithm.
static <T> 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 <E> Collection <E>	checkedCollection (Collection <E> c, Class <E> type) Returns a dynamically typesafe view of the specified collection.
static <E> List <E>	checkedList (List <E> list, Class <E> type) Returns a dynamically typesafe view of the specified list.
static <K,V> Map <K,V>	checkedMap (Map <K,V> m, Class <K> keyType, Class <V> valueType) Returns a dynamically typesafe view of the specified map.
static <E> Set <E>	checkedSet (Set <E> s, Class <E> type) Returns a dynamically typesafe view of the specified set.
static <K,V> SortedMap <K,V>	checkedSortedMap (SortedMap <K,V> m, Class <K> keyType, Class <V> valueType) Returns a dynamically typesafe view of the specified sorted map.
static <E> SortedSet <E>	checkedSortedSet (SortedSet <E> s, Class <E> type) Returns a dynamically typesafe view of the specified sorted set.
static <T> 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 <?> c2) Returns true if the two specified collections have no elements in common.
static <T> List <T>	emptyList () Returns the empty list (immutable).
static <K,V> Map <K,V>	emptyMap () Returns the empty map (immutable).
static <T> Set <T>	emptySet () Returns the empty set (immutable).
static <T> Enumeration <T>	enumeration (Collection <T> c) Returns an enumeration over the specified collection.
static <T> 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 <?> 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 <?> 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 <T> ArrayList <T>	list (Enumeration <T> 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> 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> 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 <T> List <T>	nCopies (int n, T o) Returns an immutable list consisting of n copies of the specified object.
static <T> boolean	replaceAll (List <T> 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 <T> Comparator <T>	reverseOrder () Returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.
static <T> Comparator <T>	reverseOrder (Comparator <T> 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 <T> Set <T>	singleton (T o) Returns an immutable set containing only the specified object.
static <T> List <T>	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 <T> list) Sorts the specified list into ascending order, according to the natural ordering of its elements.
static <T> void	sort (List <T> 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 <T> Collection <T>	synchronizedCollection (Collection <T> c) Returns a synchronized (thread-safe) collection backed by the specified collection.
static <T> List <T>	synchronizedList (List <T> 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 <T> Set <T>	synchronizedSet (Set <T> 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 <T> SortedSet <T>	synchronizedSortedSet (SortedSet <T> s) Returns a synchronized (thread-safe) sorted set backed by the specified sorted set.
static <T> Collection <T>	unmodifiableCollection (Collection <? extends T> c) Returns an unmodifiable view of the specified collection.
static <T> List <T>	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 <T> Set <T>	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 <T> SortedSet <T>	unmodifiableSortedSet (SortedSet <T> s) Returns an unmodifiable view of the specified sorted set.

Methods inherited from class java.lang.Object

clone , equals , finalize ,