The java.util.Collections 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.
Java Collections class fields
- static List EMPTY_LIST: This is the empty list (immutable).
- static Map EMPTY_MAP: This is the empty map (immutable).
- static Set EMPTY_SET: This is the empty set (immutable).
Java Collections class methods
| Method | Description |
| static <T> boolean addAll(Collection<? super T> c, T… elements) | This method adds all of the specified elements to the specified collection. |
| static <T> Queue<T> asLifoQueue(Deque<T> deque) | This method returns a view of a Deque as a Last-in-first-out (Lifo) Queue. |
| static <T> int binarySearch(List<? extends Comparable<? super T>> list, T key) | This method 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) | This method searches the specified list for the specified object using the binary search algorithm. |
| static <E> Collection<E> checkedCollection(Collection<E> c, Class<E> type) | This method returns a dynamically typesafe view of the specified collection. |
| static <E> List<E> checkedList(List<E> list, Class<E> type) | This method 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) |
This method returns a dynamically typesafe view of the specified map. |
| static <E> Set<E> checkedSet(Set<E> s, Class<E> type) | This method 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) | This method returns a dynamically typesafe view of the specified sorted map. |
| static <E> SortedSet<E>checkedSortedSet(SortedSet<E> s, Class<E> type) | This method returns a dynamically typesafe view of the specified sorted set. |
| static <T> void copy(List<? super T> dest, List<? extends T> src) | This method copies all of the elements from one list into another. |
| static boolean disjoint(Collection<?> c1, Collection<?> c2) | This method returns true if the two specified collections have no elements in common. |
| static <T> List<T> emptyList() | This method returns the empty list (immutable). |
| static <K,V> Map<K,V> emptyMap() | This method returns the empty map (immutable). |
| static <T> Set<T> emptySet() | This method returns the empty set (immutable). |
| static <T> Enumeration<T> enumeration(Collection<T> c) | This method returns an enumeration over the specified collection. |
| static <T> void fill(List<? super T> list, T obj) | This method replaces all of the elements of the specified list with the specified element. |
| static int frequency(Collection<?> c, Object o) | This method returns the number of elements in the specified collection equal to the specified object. |
| static int indexOfSubList(List<?> source, List<?> target) | This method 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) | This method 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) | This method 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) | This method 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) | This method 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) | This method 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) | This method 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) | This method returns an immutable list consisting of n copies of the specified object. |
| static <E> Set<E> newSetFromMap(Map<E,Boolean> map) | This method returns a set backed by the specified map. |
| static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) | This method replaces all occurrences of one specified value in a list with another. |
| static void reverse(List<?> list) | This method reverses the order of the elements in the specified list. |
| static <T> Comparator<T> reverseOrder() | This method 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) | This method returns a comparator that imposes the reverse ordering of the specified comparator. |
| static void rotate(List<?> list, int distance) | This method rotates the elements in the specified list by the specified distance. |
| static void shuffle(List<?> list) | This method randomly permutes the specified list using a default source of randomness. |
| static void shuffle(List<?> list, Random rnd) | This method randomly permute the specified list using the specified source of randomness. |
| static <T> Set<T> singleton(T o) | This method returns an immutable set containing only the specified object. |
| static <T> List<T> singletonList(T o) | This method returns an immutable list containing only the specified object. |
| static <K,V> Map<K,V> singletonMap(K key, V value) | This method returns an immutable map, mapping only the specified key to the specified value. |
| static <T extends Comparable<? super T>> void sort(List<T> list) | This method 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) | This method sorts the specified list according to the order induced by the specified comparator. |
| static void swap(List<?> list, int i, int j) | This method swaps the elements at the specified positions in the specified list. |
| static <T> Collection<T> synchronizedCollection(Collection<T> c) | This method returns a synchronized (thread-safe) collection backed by the specified collection. |
| static <T> List<T>
synchronizedList(List<T> list) |
This method returns a synchronized (thread-safe) list backed by the specified list. |
| static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) | This method returns a synchronized (thread-safe) map backed by the specified map. |
| static <T> Set<T> synchronizedSet(Set<T> s) | This method returns a synchronized (thread-safe) set backed by the specified set. |
| static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) | This method returns a synchronized (thread-safe) sorted map backed by the specified sorted map. |
| static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) | This method returns a synchronized (thread-safe) sorted set backed by the specified sorted set. |
| static <T> Collection<T> unmodifiableCollection
(Collection<? extends T> c) |
This method returns an unmodifiable view of the specified collection. |
| static <T> List<T>
unmodifiableList(List<? extends T> list) |
This method returns an unmodifiable view of the specified list. |
| static <K,V> Map<K,V> unmodifiableMap(Map<? extends K,? extends V> m) | This method returns an unmodifiable view of the specified map. |
| static <T> Set<T>
unmodifiableSet(Set<? extends T> s) |
This method returns an unmodifiable view of the specified set. |
| static <K,V> SortedMap<K,V> unmodifiableSortedMap
(SortedMap<K,? extends V> m) |
This method returns an unmodifiable view of the specified sorted map. |
| static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) | This method returns an unmodifiable view of the specified sorted set. |
Java Collections class examples
- Java Collections class
- How to add all elements to the given collection object?
- Java Collections.asLifoQueue() method
- How to search user defined object from a List by using binary search using comparator?
- Java Collections.checkedCollection() method
- Java Collections.checkedList() method
- Java Collections.checkedSet() method
- Java Collections.checkedMap() method
- Java Collections.disjoint() method
- How to create empty list using Collections class?
- How to create empty set using Collections class?
- How to create empty map using Collections class?/a>
- Java enumeration for arraylist
- How to replace element in list java?
- How to find repeated element count in a collection?
- How to convert enumeration to list in java?
- How to get index of a sub list from another list?
- How to get last index of a sub list from another list?
- How to get max element from the given list?
- How to get min element from the given list?
- How to get max element of a list of user defined objects?
- How to get min element of a list of user defined objects?
- How to get max element of a list of user defined objects using Comparator?
- How to get min element of a list of user defined objects using Comparator?
- How to create multiple copies of a given object?
- How to replace all occurrences of a given object in the list?
- How to rotate element in list java?
- How to create synchronized list in java?
- How to create synchronized set?
- How to create synchronized map?
- How to create immutable list in java?
- How to create immutable set in java?
- How to create immutable map in java?
