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Java Collections Class

By Princy VictorPrincy Victor

Home » Software Development » Software Development Tutorials » Java Tutorial » Java Collections Class

Java-Collections-Class

Introduction to Java Collections Class

In Java, an individual object’s group is represented as one unit known as Collection. This framework defines multiple classes and interfaces to denote a group of objects as a single unit. In addition to that, several other features are also present for the Java Collections Class. It includes:

  • Two important root interfaces are the Collection interface and Map interface of the packages java.util.Collection and java.util.Map respectively.
  • If the collections of objects of the class are null, then NullPointerException will be thrown.
  • Polymorphic algorithms are supported.

Declaration and Methods of Java Collections Class

More details on the Java Collections Class will be discussed in the following sections.

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Declaration

Java Collections Class can be declared using the below syntax:

Syntax:

public class Collections extends Object

Methods

Now, let us see some of the commonly used methods in the Java Collections Class.

  • addAll(Collection<? super T> c, T… elements): Every element will be added to the mentioned collection on calling this method.
  • binarySearch(List<? extends Comparable<? super T>> list, T key): Mentioned list will be searched for the specified object with the help of a binary search algorithm.
  • binarySearch(List<? extends T> list, T key, Comparator<? super T> c): Mentioned list will be searched for the specified object with the help of a binary search algorithm.
  • asLifoQueue(Deque<T> deque): Deque view will be returned similar to LIFO(Last-in-First-Out) queue.
  • checkedCollection(Collection<E> c, Class<E> type): The typesafe view, which is dynamic, will be returned for the collection mentioned.
  • checkedList(List<E> list, Class<E> type): The typesafe view, which is dynamic, will be returned for the list mentioned.
  • checkedMap(Map<K,V> m, Class<K> keyType, Class<V> valueType): The typesafe view which is dynamic will be returned for the map mentioned.
  • checkedSet(Set<E> s, Class<E> type): The typesafe view, which is dynamic, will be returned for the set mentioned.
  • checkedSortedMap(SortedMap<K,V> m, Class<K> keyType, Class<V> valueType): The typesafe view which is dynamic will be returned for the sorted map mentioned.
  • checkedSortedSet(SortedSet<E> s, Class<E> type): The typesafe view, which is dynamic, will be returned for the sorted set mentioned.
  • emptyEnumeration(): An enumeration will be returned which has no elements.
  • emptyIterator(): An iterator will be returned which has no elements.
  • emptyList(): An empty list will be returned, which is immutable.
  • emptyListIterator(): A list iterator will be returned which has no elements.
  • emptyMap(): An empty map will be returned, which is immutable.
  • emptySet(): An empty set will be returned, which is immutable.
  • copy(List<? super T> dest, List<? extends T> src): Elements from one list will be copied into another.
  • disjoint(Collection<?> c1, Collection<?> c2): If no elements are common for the mentioned two collections, true will be returned.
  • enumeration(Collection<T> c): An enumeration will be returned over the collection mentioned.
  • fill(List<? super T> list, T obj): Elements of the list mentioned will be replaced with the element mentioned.
  • frequency(Collection<?> c, Object o): Count of the elements in the collection will be returned that are equal to the object mentioned.
  • lastIndexOfSubList(List<?> source, List<?> target): The beginning position of the last occurrence of the target list mentioned will be returned. If no such occurrences are there, -1 will be returned.
  • indexOfSubList(List<?> source, List<?> target): The beginning position of the first occurrence of the target list mentioned will be returned. If no such occurrences are there, -1 will be returned.
  • list(Enumeration<T> e): An array list will be returned, which contains the elements returned by the enumeration mentioned in the order where the enumeration is returned.
  • unmodifiableCollection (Collection<? extends T> c): An unmodifiable view will be returned for the collection mentioned.
  • unmodifiableList (List<? extends T> list): An unmodifiable view will be returned for the list mentioned.
  • unmodifiableMap (Map<? extends K,? extends V> m): An unmodifiable view will be returned for the map mentioned.
  • unmodifiableSet (Set<? extends T> s): An unmodifiable view will be returned for the set mentioned.
  • unmodifiableSortedMap (SortedMap<K,? extends V> m): An unmodifiable view will be returned for the sorted map mentioned.
  • unmodifiableSortedSet (SortedSet<T> s): An unmodifiable view will be returned for the sorted set mentioned.
  • max(Collection<? extends T> coll): The largest element of the collection will be returned based on the element’s natural ordering.
  • max(Collection<? extends T> coll, Comparator<? super T> comp): The largest element of the collection will be returned based on the comparator provided.
  • min(Collection<? extends T> coll): The minimum element of the collection will be returned based on the element’s natural ordering.
  • min(Collection<? extends T> coll, Comparator<? super T> comp): The minimum element of the collection will be returned based on the comparator provided.
  • replaceAll(List<T> list, T oldVal, T newVal): Every occurrence of the value mentioned in the list will be replaced with another.
  • nCopies(int n, T o): An immutable list will be returned, containing n copies of the object mentioned.
  • newSetFromMap(Map< E,Boolean> map): A set will be returned, which is backed by the map mentioned.
  • reverse(List<?> list): Elements in the list mentioned will be reversed.
  • reverseOrder(): A comparator will be returned that makes the objects ordering reverse that can implement a Comparable interface.
  • shuffle(List<?> list): The list mentioned will be shuffled based on the randomness.
  • reverseOrder (Comparator<T> cmp): A comparator will be returned that makes the specified comparator’s ordering reverse.
  • rotate(List<?> list, int distance): Elements in the list mentioned will be rotated by the distance specified.
  • shuffle(List<?> list, Random rnd): The list mentioned will be permuted randomly based on the randomness.
  • singleton(T o): An immutable set will be returned that contains only the object mentioned.
  • singletonList(T o): An immutable list will be returned that contains only the object mentioned.
  • singletonMap(K key, V value): An immutable map will be returned that maps only the key mentioned to a particular value.
  • sort(List<T> list): The list mentioned will be sorted based on the natural ordering.
  • sort(List<T> list, Comparator<? super T> c): The list mentioned will be sorted based on the comparator mentioned.
  • swap(List<?> list, int i, int j): Elements in the list mentioned will be swapped based on the positions mentioned.
  • synchronizedCollection (Collection<T> c): A synchronized collection that is thread-safe will be returned, which is backed by the collection mentioned.
  • synchronizedList (List<T> list): A synchronized list that is thread-safe will be returned, which is backed by the list mentioned.
  • synchronizedMap (Map<K,V> m): A synchronized map that is thread-safe will be returned, which is backed by the map mentioned.
  • synchronizedSet (Set<T> s): A synchronized set that is thread-safe will be returned, which is backed by the set mentioned.
  • synchronizedSortedMap (SortedMap<K,V> m): A synchronized sorted map that is thread-safe will be returned, which is backed by the sorted map mentioned.
  • synchronizedSortedSet (SortedSet<T> s): A synchronized sorted set that is thread-safe will be returned, which is backed by the sorted set mentioned.

Recommended Articles

This is a guide to Java Collections Class. Here we discuss the Introduction to Java Collections Class along with its declaration and different methods. You may also have a look at the following articles to learn more –

  1. Java OffsetDateTime
  2. Association in Java
  3. Java Stream Filter
  4. Java Transient

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