What is Collection interface in Java

Constance 145 Published: 10/12/2024

What is Collection interface in Java

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In Java, the Collection interface is a fundamental part of the Java Collections Framework (JCF). It defines a set of methods that can be used to manipulate and traverse collections of objects. A collection is an object that stores multiple values and allows you to access, add, or remove them.

The Collection interface has several key characteristics:

Immutability: By default, a Collection instance is immutable, meaning its contents cannot be changed after it's created. Homogeneity: A Collection can only contain objects of the same class or type (e.g., all strings or all integers). Order-Independence: The order in which elements are stored in a Collection does not matter, as the interface only provides methods for adding and removing elements.

The Collection interface has several methods that can be used to manipulate and traverse its contents:

void add(E e): Adds an element to the collection. boolean addAll(Collection<? extends E> c): Adds all elements from another collection to this one. int size(): Returns the number of elements in the collection. boolean isEmpty(): Returns whether the collection is empty (i.e., has no elements). void clear(): Removes all elements from the collection. boolean contains(Object o): Returns whether the collection contains a specific element. int hashCode(): Returns a hash code value for the collection.

Subinterfaces of Collection include:

List: A sequence of elements, allowing access and modification via an index (e.g., by using a numerical index). Set: A collection without duplicates or duplicate entries allowed. Queue: A first-in, first-out (FIFO) data structure for adding and removing elements.

By implementing the Collection interface, you can create your own custom collections that support various operations like adding, removing, and traversing its contents. This is particularly useful when working with complex data structures or domain-specific requirements that aren't met by existing collection classes.

In summary, the Collection interface in Java provides a foundation for creating and manipulating collections of objects, offering a range of methods for adding, removing, and querying elements within. Its versatility makes it an essential part of Java programming, allowing developers to create custom data structures tailored to specific needs.

Methods of Collection interface in Java

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Methods of Collection Interface in Java:

The Collection interface is a fundamental part of the Java Collections Framework (JCF), which provides classes and interfaces for working with collections of objects. The Collection interface itself defines several methods that allow you to manipulate, traverse, and query the elements contained within a collection.

Here are some common methods provided by the Collection interface:

size(): Returns the number of elements in this collection. This method is useful for determining the size of the collection before performing an operation that requires knowing the collection's size.

int size();

isEmpty(): Tests whether this collection has no elements. This method checks if the collection is empty or not by checking the number of elements returned by size().

boolean isEmpty();

contains(Object o): Returns true if this collection contains an element equal to the specified object. This method checks if the given object exists in the collection.

boolean contains(Object o);

containsAll(Collection c): Returns true if this collection contains all elements of the specified collection.

boolean containsAll(Collection c);

add(E e): Adds an element to this collection. This method is used to insert a new element into the collection.

void add(E e);

addAll(Collection<? extends E> c): Inserts all elements contained in the specified collection into this collection (optional operation).

void addAll(Collection c);

remove(Object o): Removes a single instance of an object from the collection.

boolean remove(Object o);

clear(): Removes all elements from the collection.

void clear();

toArray(): Returns an array containing all of the elements in this collection, in order.

Object[] toArray();

iterator(): Returns a new Iterator that iterates over the elements contained in this collection (in apparent lexical order).

Iterator iterator();

listIterator(int index): Returns a new ListIterator for this list that has been positioned at the given index.

ListIterator listIterator(int index);

spliterator(): Creates a late-binding Spliterator from this collection.

Spliterator spliterator();

These are some of the common methods provided by the Collection interface in Java. Each method has its own specific purpose and usage, making it an essential part of working with collections.

Additional information:

The Collection interface is implemented by several classes such as ArrayList, LinkedList, HashSet, TreeSet, etc. Implementing your own collection class would require implementing these methods correctly to ensure the correct functionality and efficiency of your custom collection.

References:

https://docs.oracle.com/javase/8/docs/api/java/util/Collection.html

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