java.util

Class Collections

java.lang.Object

java.util.Collections

public class Collections
extends Object

Utility methods that operate on collections. See the official Java API doc for details.

Field Summary

Fields

Modifier and Type	Field and Description
static List	EMPTY_LIST
static Map	EMPTY_MAP
static Set	EMPTY_SET

Method Summary

Modifier and Type	Method and Description
static <T> boolean	addAll(Collection<? super T> c, T... a)
static <T> Queue<T>	asLifoQueue(Deque<T> deque)
static <T> int	binarySearch(List<? extends Comparable<? super T>> sortedList, T key) Perform a binary search on a sorted List, using natural ordering.
static <T> int	binarySearch(List<? extends T> sortedList, T key, Comparator<? super T> comparator) Perform a binary search on a sorted List, using a user-specified comparison function.
static <T> void	copy(List<? super T> dest, List<? extends T> src)
static boolean	disjoint(Collection<?> c1, Collection<?> c2)
static <T> Iterator<T>	emptyIterator()
static <T> List<T>	emptyList()
static <T> ListIterator<T>	emptyListIterator()
static <K,V> Map<K,V>	emptyMap()
static <T> Set<T>	emptySet()
static <T> Enumeration<T>	enumeration(Collection<T> c)
static <T> void	fill(List<? super T> list, T obj)
static int	frequency(Collection<?> c, Object o)
static <T> ArrayList<T>	list(Enumeration<T> e)
static <T extends Object & Comparable<? super T>> T	max(Collection<? extends T> coll)
static <T> T	max(Collection<? extends T> coll, Comparator<? super T> comp)
static <T extends Object & Comparable<? super T>> T	min(Collection<? extends T> coll)
static <T> T	min(Collection<? extends T> coll, Comparator<? super T> comp)
static <T> List<T>	nCopies(int n, T o)
static <E> Set<E>	newSetFromMap(Map<E,Boolean> map)
static <T> boolean	replaceAll(List<T> list, T oldVal, T newVal)
static void	reverse(List<?> l)
static <T> Comparator<T>	reverseOrder()
static <T> Comparator<T>	reverseOrder(Comparator<T> cmp)
static void	rotate(List<?> lst, int dist) Rotates the elements in list by the distance dist
static void	shuffle(List<?> list)
static void	shuffle(List<?> list, Random rnd)
static <T> Set<T>	singleton(T o)
static <T> List<T>	singletonList(T o)
static <K,V> Map<K,V>	singletonMap(K key, V value)
static <T> void	sort(List<T> target)
static <T> void	sort(List<T> target, Comparator<? super T> c)
static void	swap(List<?> list, int i, int j)
static <T> Collection<T>	unmodifiableCollection(Collection<? extends T> coll)
static <T> List<T>	unmodifiableList(List<? extends T> list)
static <K,V> Map<K,V>	unmodifiableMap(Map<? extends K,? extends V> map)
static <T> Set<T>	unmodifiableSet(Set<? extends T> set)
static <K,V> SortedMap<K,V>	unmodifiableSortedMap(SortedMap<K,? extends V> map)
static <T> SortedSet<T>	unmodifiableSortedSet(SortedSet<T> set)

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, toString

Field Detail

EMPTY_LIST

public static final List EMPTY_LIST

EMPTY_MAP

public static final Map EMPTY_MAP

EMPTY_SET

public static final Set EMPTY_SET

Method Detail

addAll

public static <T> boolean addAll(Collection<? super T> c,
                                 T... a)

asLifoQueue

public static <T> Queue<T> asLifoQueue(Deque<T> deque)

binarySearch

public static <T> int binarySearch(List<? extends Comparable<? super T>> sortedList,
                                   T key)

Perform a binary search on a sorted List, using natural ordering.

Note: The GWT implementation differs from the JDK implementation in that it does not do an iterator-based binary search for Lists that do not implement RandomAccess.

Parameters:

sortedList - object array to search

key - value to search for

Returns:

the index of an element with a matching value, or a negative number which is the index of the next larger value (or just past the end of the array if the searched value is larger than all elements in the array) minus 1 (to ensure error returns are negative)

Throws:

ClassCastException - if key is not comparable to sortedList's elements.

binarySearch

public static <T> int binarySearch(List<? extends T> sortedList,
                                   T key,
                                   Comparator<? super T> comparator)

Perform a binary search on a sorted List, using a user-specified comparison function.

Note: The GWT implementation differs from the JDK implementation in that it does not do an iterator-based binary search for Lists that do not implement RandomAccess.

Parameters:

sortedList - List to search

key - value to search for

comparator - comparision function, null indicates natural ordering should be used.

Returns:

the index of an element with a matching value, or a negative number which is the index of the next larger value (or just past the end of the array if the searched value is larger than all elements in the array) minus 1 (to ensure error returns are negative)

Throws:

ClassCastException - if key and sortedList's elements cannot be compared by comparator.

copy

public static <T> void copy(List<? super T> dest,
                            List<? extends T> src)

disjoint

public static boolean disjoint(Collection<?> c1,
                               Collection<?> c2)

emptyIterator

public static <T> Iterator<T> emptyIterator()

emptyList

public static <T> List<T> emptyList()

emptyListIterator

public static <T> ListIterator<T> emptyListIterator()

emptyMap

public static <K,V> Map<K,V> emptyMap()

emptySet

public static <T> Set<T> emptySet()

enumeration

public static <T> Enumeration<T> enumeration(Collection<T> c)

fill

public static <T> void fill(List<? super T> list,
                            T obj)

frequency

public static int frequency(Collection<?> c,
                            Object o)

list

public static <T> ArrayList<T> list(Enumeration<T> e)

max

public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll)

max

public static <T> T max(Collection<? extends T> coll,
                        Comparator<? super T> comp)

min

public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll)

min

public static <T> T min(Collection<? extends T> coll,
                        Comparator<? super T> comp)

newSetFromMap

public static <E> Set<E> newSetFromMap(Map<E,Boolean> map)

nCopies

public static <T> List<T> nCopies(int n,
                                  T o)

replaceAll

public static <T> boolean replaceAll(List<T> list,
                                     T oldVal,
                                     T newVal)

reverse

public static void reverse(List<?> l)

reverseOrder

public static <T> Comparator<T> reverseOrder()

reverseOrder

public static <T> Comparator<T> reverseOrder(Comparator<T> cmp)

rotate

public static void rotate(List<?> lst,
                          int dist)

Rotates the elements in list by the distance dist

e.g. for a given list with elements [1, 2, 3, 4, 5, 6, 7, 8, 9, 0], calling rotate(list, 3) or rotate(list, -7) would modify the list to look like this: [8, 9, 0, 1, 2, 3, 4, 5, 6, 7]

Parameters:

lst - the list whose elements are to be rotated.

dist - is the distance the list is rotated. This can be any valid integer. Negative values rotate the list backwards.

shuffle

public static void shuffle(List<?> list)

shuffle

public static void shuffle(List<?> list,
                           Random rnd)

singleton

public static <T> Set<T> singleton(T o)

singletonList

public static <T> List<T> singletonList(T o)

singletonMap

public static <K,V> Map<K,V> singletonMap(K key,
                                          V value)

sort

public static <T> void sort(List<T> target)

sort

public static <T> void sort(List<T> target,
                            Comparator<? super T> c)

swap

public static void swap(List<?> list,
                        int i,
                        int j)

unmodifiableCollection

public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> coll)

unmodifiableList

public static <T> List<T> unmodifiableList(List<? extends T> list)

unmodifiableMap

public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K,? extends V> map)

unmodifiableSet

public static <T> Set<T> unmodifiableSet(Set<? extends T> set)

unmodifiableSortedMap

public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K,? extends V> map)

unmodifiableSortedSet

public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> set)