Java Utility Library
Java Utility Library

Java.util.Collections Class

Java Collections Class

Java.util package provides a Collections class which 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. The methods of this class all throw a NullPointerException if the collections or class objects provided to them are null.

Class declaration

The declaration of java.util.Collections class is:

public class Collections
  extends Object

Fields

Following are the fields for java.util.Collections class:

S.NField & Description
1. static List EMPTY_LIST
The empty list (immutable).
2. static Map EMPTY_MAP
The empty map (immutable).
3. static Set EMPTY_SET
The empty set (immutable).

java.util.Collections Methods

The java.util.Collections class has a number of methods which are listed below:

Member Methods

S.NMethods & Description
1. static <T> boolean addAll(Collection<? super T> c, T... elements)
Adds all of the specified elements to the specified collection.
2. static <T> Queue<T> asLifoQueue(Deque<T> deque)
Returns a view of a Deque as a Last-in-first-out (Lifo) Queue.
3. 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.
4. 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.
5. static <E> Collection<E> checkedCollection(Collection<E> c, Class<E> type)
Returns a dynamically typesafe view of the specified collection.
6. static <E> List<E> checkedList(List<E> list, Class<E> type)
Returns a dynamically typesafe view of the specified list.
7. 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.
8. static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K,V> m, Class<K> keyType, Class<V> valueType)
Returns a dynamically typesafe view of the specified navigable map.
9. static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s, Class<E> type)
Returns a dynamically typesafe view of the specified navigable set.
10. static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type)
Returns a dynamically typesafe view of the specified queue.
11. static <E> Set<E> checkedSet(Set<E> s, Class<E> type)
Returns a dynamically typesafe view of the specified set.
12. 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.
13. static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, Class<E> type)
Returns a dynamically typesafe view of the specified sorted set.
14. static <T> void copy(List<? super T> dest, List<? extends T> src)
Copies all of the elements from one list into another.
15. static boolean disjoint(Collection<?> c1, Collection<?> c2)
Returns true if the two specified collections have no elements in common.
16. static <T> Enumeration<T> emptyEnumeration()
Returns an enumeration that has no elements.
17. static <T> Iterator<T> emptyIterator()
Returns an iterator that has no elements.
18. static <T> List<T> emptyList()
Returns an empty list (immutable).
19. static <T> ListIterator<T> emptyListIterator()
Returns a list iterator that has no elements.
20. static <K,V> Map<K,V> emptyMap()
Returns an empty map (immutable).
21. static <K,V> NavigableMap<K,V> emptyNavigableMap()
Returns an empty navigable map (immutable).
22. static <E> NavigableSet<E> emptyNavigableSet()
Returns an empty navigable set (immutable).
23. static <T> Set<T> emptySet()
Returns an empty set (immutable).
24. static <K,V> SortedMap<K,V> emptySortedMap()
Returns an empty sorted map (immutable).
25. static <E> SortedSet<E> emptySortedSet()
Returns an empty sorted set (immutable).
26. static <T> Enumeration<T> enumeration(Collection<T> c)
Returns an enumeration over the specified collection.
27. static <T> void fill(List<? super T> list, T obj)
Replaces all of the elements of the specified list with the specified element.
28. static int frequency(Collection<?> c, Object o)
Returns the number of elements in the specified collection equal to the specified object.
29. 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.
30. 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.
31. 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.
32. 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.
33. 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.
34. 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.
35. 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.
36. static <T> List<T> nCopies(int n, T o)
Returns an immutable list consisting of n copies of the specified object.
37. static <E> Set<E> newSetFromMap(Map<E,Boolean> map)
Returns a set backed by the specified map.
38. static <T> boolean replaceAll(List<T> list, T oldVal, T newVal)
Replaces all occurrences of one specified value in a list with another.
39. static void reverse(List<?> list)
Reverses the order of the elements in the specified list.
40. 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.
41. static <T> Comparator<T> reverseOrder(Comparator<T> cmp)
Returns a comparator that imposes the reverse ordering of the specified comparator.
42. static void rotate(List<?> list, int distance)
Rotates the elements in the specified list by the specified distance.
43. static void shuffle(List<?> list)
Randomly permutes the specified list using a default source of randomness.
44. static void shuffle(List<?> list, Random rnd)
Randomly permute the specified list using the specified source of randomness.
45. static <T> Set<T> singleton(T o)
Returns an immutable set containing only the specified object.
46. static <T> List<T> singletonList(T o)
Returns an immutable list containing only the specified object.
47. static <K,V> Map<K,V> singletonMap(K key, V value)
Returns an immutable map, mapping only the specified key to the specified value.
48. 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.
49. static <T> void sort(List<T> list, Comparator<? super T> c)
Sorts the specified list according to the order induced by the specified comparator.
50. static void swap(List<?> list, int i, int j)
Swaps the elements at the specified positions in the specified list.
51. static <T> Collection<T> synchronizedCollection(Collection<T> c)
Returns a synchronized (thread-safe) collection backed by the specified collection.
52. static <T> List<T> synchronizedList(List<T> list)
Returns a synchronized (thread-safe) list backed by the specified list.
53. static <K,V> Map<K,V> synchronizedMap(Map<K,V> m)
Returns a synchronized (thread-safe) map backed by the specified map.
54. static <K,V> NavigableMap<K,V> synchronizedNavigableMap(NavigableMap<K,V> m)
Returns a synchronized (thread-safe) navigable map backed by the specified navigable map.
55. static <T> NavigableSet<T> synchronizedNavigableSet(NavigableSet<T> s)
Returns a synchronized (thread-safe) navigable set backed by the specified navigable set.
56. static <T> Set<T> synchronizedSet(Set<T> s)
Returns a synchronized (thread-safe) set backed by the specified set.
57. static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m)
Returns a synchronized (thread-safe) sorted map backed by the specified sorted map.
58. static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s)
Returns a synchronized (thread-safe) sorted set backed by the specified sorted set.
59. static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c)
Returns an unmodifiable view of the specified collection.
60. static <T> List<T> unmodifiableList(List<? extends T> list)
Returns an unmodifiable view of the specified list.
61. static <K,V> Map<K,V> unmodifiableMap(Map<? extends K,? extends V> m)
Returns an unmodifiable view of the specified map.
62. static <K,V> NavigableMap<K,V> unmodifiableNavigableMap(NavigableMap<K,? extends V> m)
Returns an unmodifiable view of the specified navigable map.
63. static <T> NavigableSet<T> unmodifiableNavigableSet(NavigableSet<T> s)
Returns an unmodifiable view of the specified navigable set.
64. static <T> Set<T> unmodifiableSet(Set<? extends T> s)
Returns an unmodifiable view of the specified set.
65. static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K,? extends V> m)
Returns an unmodifiable view of the specified sorted map.
66. static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s)
Returns an unmodifiable view of the specified sorted set.

Methods inherited

This class inherits the methods of following class:

  • java.lang.Object
AlphaCodingSkills
AlphaCodingSkills Android App
Facebook Page Twitter Page LinkedIn Page
Learning Tutorials
Learning Tutorials
Useful Links
Python Libraries
About Us  |  Privacy Policy  |  Contact Us
AlphaCodingSkills is a online learning portal that provides tutorials on Python, Java, C++, C, C#, PHP, R, Ruby, Rust, Scala, Swift, Perl, SQL, Data Structures and Algorithms. Tutorials, examples, references and content of the website are reviewed and simplified continuously to improve comprehensibility and eliminate any possible error. We use cookies to ensure best browsing experience on our website. While using this website, you acknowledge to have read and accepted our cookie and privacy policy.