A2oz

What are the methods defined in the Collection interface?

Published in Java Programming 2 mins read

The Collection interface in Java defines a set of methods that provide common operations for storing and manipulating a group of objects. These methods allow you to add, remove, search, and iterate over elements within a collection.

Here's a breakdown of the methods defined in the Collection interface:

Core Methods:

  • add(E e): Adds the specified element to the collection.
  • addAll(Collection<? extends E> c): Adds all elements from the specified collection to this collection.
  • clear(): Removes all elements from the collection.
  • contains(Object o): Checks if the collection contains the specified element.
  • containsAll(Collection<?> c): Checks if the collection contains all elements from the specified collection.
  • isEmpty(): Checks if the collection is empty.
  • iterator(): Returns an iterator over the elements in the collection.
  • remove(Object o): Removes the specified element from the collection.
  • removeAll(Collection<?> c): Removes all elements from the collection that are contained in the specified collection.
  • retainAll(Collection<?> c): Retains only the elements in the collection that are also contained in the specified collection.
  • size(): Returns the number of elements in the collection.
  • toArray(): Returns an array containing all elements in the collection.
  • toArray(T[] a): Returns an array containing all elements in the collection, using the specified array if possible.

Example:

import java.util.ArrayList;
import java.util.Collection;

public class CollectionExample {
    public static void main(String[] args) {
        Collection<String> names = new ArrayList<>();

        // Adding elements
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        // Checking size
        System.out.println("Number of names: " + names.size()); // Output: 3

        // Checking if contains an element
        System.out.println("Contains Bob? " + names.contains("Bob")); // Output: true

        // Removing an element
        names.remove("Bob");

        // Iterating over elements
        for (String name : names) {
            System.out.println(name); // Output: Alice, Charlie
        }
    }
}

These methods provide a foundation for working with collections in Java, allowing you to perform various operations efficiently.

Related Articles