The Java Collections class consists exclusively of static methods that operate on or return collections.Following are the important points about Collections −
Sr.No. Method & Description 1 static <T> boolean addAll(Collection<? super T> c, T... elements)This method adds all of the specified elements to the specified collection.
2 static <T> Queue<T> asLifoQueue(Deque<T> deque)This method 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)This method searches the specified list for the specified object using the binary search algorithm.
4 static <E> Collection<E> checkedCollection(Collection<E> c, Class<E> type)This method returns a dynamically typesafe view of the specified collection.
5 static <E> List<E> checkedList(List<E> list, Class<E> type)This method returns a dynamically typesafe view of the specified list.
6 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.
7 static <K,V> Navigable<K,V> checkedNavigableMap(Navigable<K,V> m, Class<K> keyType, Class<V> valueType)This method returns a dynamically typesafe view of the specified navigable map.
8 static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s, Class<E> type)This method returns a dynamically typesafe view of the specified navigable set.
9 static <E> Queue<E> checkedQueue(Queue<E> s, Class<E> type)This method returns a dynamically typesafe view of the specified queue.
10 static <E> Set<E> checkedSet(Set<E> s, Class<E> type)This method returns a dynamically typesafe view of the specified set.
11 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.
12 static <E> SortedSet<E>checkedSortedSet(SortedSet<E> s, Class<E> type)This method returns a dynamically typesafe view of the specified sorted set.
13 static <T> void copy(List<? super T> dest, List<? extends T> src)This method copies all of the elements from one list into another.
14 static boolean disjoint(Collection<?> c1, Collection<?> c2)This method returns true if the two specified collections have no elements in common.
15 static <T> Enumeration <T> emptyEnumeration()This method returns the empty enumeration.
16 static <T> Iterator <T> emptyIterator()This method returns the empty iterator.
17 static <T> List<T> emptyList()This method returns the empty list (immutable).
18 static <T> ListIterator <T> emptyListIterator()This method returns the empty list iterator.
19 static <K,V> Map<K,V> emptyMap()This method returns the empty map (immutable).
20 static <K,V> NavigableMap<K,V> emptyNavigableMap()This method returns the empty navigable map (immutable).
21 static <T> NavigableSet<T> emptyNavigableSet()This method returns the empty navigable set (immutable).
22 static <T> Set<T> emptySet()This method returns the empty set (immutable).
23 static <K,V> SortedMap<K,V> emptySortedMap()This method returns the empty sorted map (immutable).
24 static <T> SortedSet<T> emptySortedSet()This method returns the empty sorted set (immutable).
25 static <T> Enumeration<T> enumeration(Collection<T> c)This method returns an enumeration over the specified collection.
26 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.
27 static int frequency(Collection<?> c, Object o)This method returns the number of elements in the specified collection equal to the specified object.
28 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.
29 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.
30 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.
31 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.
32 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.
33 static <T> List<T> nCopies(int n, T o)This method returns an immutable list consisting of n copies of the specified object.
34 static <E> Set<E> newSetFromMap(Map<E,Boolean> map)This method returns a set backed by the specified map.
35 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.
36 static void reverse(List<?> list)This method reverses the order of the elements in the specified list.
37 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.
38 static void rotate(List<?> list, int distance)This method rotates the elements in the specified list by the specified distance.
39 static void shuffle(List<?> list)This method randomly permutes the specified list using a default source of randomness.
40 static <T> Set<T> singleton(T o)This method returns an immutable set containing only the specified object.
41 static <T> List<T> singletonList(T o)This method returns an immutable list containing only the specified object.
42 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.
43 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.
44 static void swap(List<?> list, int i, int j)This method swaps the elements at the specified positions in the specified list.
45 static <T> Collection<T> synchronizedCollection(Collection<T> c)This method returns a synchronized (thread-safe) collection backed by the specified collection.
46 static <T> List<T> synchronizedList(List<T> list)This method returns a synchronized (thread-safe) list backed by the specified list.
47 static <K,V> Map<K,V> synchronizedMap(Map<K,V> m)This method returns a synchronized (thread-safe) map backed by the specified map.
48 static <K,V> NavigableMap<K,V> synchronizedNavigableMap()This method returns the synchronized navigable map (immutable).
49 static <T> NavigableSet<T> synchronizedNavigableSet()This method returns the synchronized navigable set (immutable).
50 static <T> Set<T> synchronizedSet(Set<T> s)This method returns a synchronized (thread-safe) set backed by the specified set.
51 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.
52 static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s)This method returns a synchronized (thread-safe) sorted set backed by the specified sorted set.
53 static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c)This method returns an unmodifiable view of the specified collection.
54 static <T> List<T> unmodifiableList(List<? extends T> list)This method returns an unmodifiable view of the specified list.
55 static <K,V> Map<K,V> unmodifiableMap(Map<? extends K,? extends V> m)This method returns an unmodifiable view of the specified map.
56 static <K,V> NavigableMap<K,V> unmodifiableNavigableMap()This method returns the unmodifiable navigable map (immutable).
57 static <T> NavigableSet<T> unmodifiableNavigableSet()This method returns the unmodifiable navigable set (immutable).
58 static <T> Set<T> unmodifiableSet(Set<? extends T> s)This method returns an unmodifiable view of the specified set.
59 static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K,? extends V> m)This method returns an unmodifiable view of the specified sorted map.
60 static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s)This method returns an unmodifiable view of the specified sorted set.
The following example shows the usage of Java Collection addAll(Collection,T... ) method to add a collection of Integers. We've created a List object with some integers, printed the original list. Using addAll(collection, T...) method, we've added few more elements to the list and then printed the updated list.
Let us compile and run the above program, this will produce the following result −
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