The class collections 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.
Sorting Methods
sort(List<T> list): Sorts the specified list in ascending order using natural ordering of elements.sort(List<T> list, Comparator<? super T> c): Sorts the specified list according to the order induced by the specified comparator.reverse(List<?> list): Reverses the order of the elements in the specified list.shuffle(List<?> list): Randomly permutes the specified list.
Searching Methods
binarySearch(List<? extends Comparable<? super T>> list, T key): Searches the specified list for the specified object using the binary search algorithm.binarySearch(List<? extends T> list, T key, Comparator<? super T> c): Searches the specified list for the specified object using the binary search algorithm.
Synchronization Methods
synchronizedCollection(Collection<T> c): Returns a synchronized (thread-safe) collection backed by the specified collection.synchronizedList(List<T> list): Returns a synchronized (thread-safe) list backed by the specified list.synchronizedMap(Map<K,V> m): Returns a synchronized (thread-safe) map backed by the specified map.synchronizedSet(Set<T> s): Returns a synchronized (thread-safe) set backed by the specified set.
Miscellaneous Methods
copy(List<? super T> dest, List<? extends T> src): Copies all of the elements from one list into another.fill(List<? super T> list, T obj): Replaces all of the elements of the specified list with the specified element.frequency(Collection<?> c, Object o): Returns the number of elements in the specified collection equal to the specified object.max(Collection<? extends T> coll): Returns the maximum element of the given collection, according to the natural ordering of its elements.min(Collection<? extends T> coll): Returns the minimum element of the given collection, according to the natural ordering of its elements.replaceAll(List<T> list, T oldVal, T newVal): Replaces all occurrences of one specified value in a list with another specified value.