Collection Interface

The Collection Interface is the root interface of the Java Collections Framework. It represents a group of objects, known as elements. The Collection interface provides fundamental methods to work with elements, such as adding, removing, and querying elements in a collection. All other collection interfaces (Set, List, Queue, etc.) extend this interface.

Key Methods in Collection Interface

  1. add(E e):

    • Adds the specified element to the collection. Returns true if the element was successfully added.
    collection.add("Alice");

  2. remove(Object o):

    • Removes the specified element from the collection. Returns true if the element was found and removed.
    collection.remove("Alice");

  3. size():

    • Returns the number of elements in the collection.
    int size = collection.size();

  4. isEmpty():

    • Checks if the collection is empty. Returns true if the collection contains no elements.
    boolean empty = collection.isEmpty();

  5. contains(Object o):

    • Checks if the collection contains the specified element.
    boolean hasAlice = collection.contains("Alice");

  6. clear():

    • Removes all elements from the collection.
    collection.clear();

  7. iterator():

    • Returns an iterator that can be used to traverse the elements of the collection.
    Iterator<E> iterator = collection.iterator();

Example: Using Collection Interface

import java.util.*;

public class CollectionInterfaceExample {
    public static void main(String[] args) {
        // Creating a Collection (List implementation)
        Collection<String> names = new ArrayList<>();
        
        // Adding elements
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
        
        // Iterating through the collection
        for (String name : names) {
            System.out.println(name);
        }
        
        // Removing an element
        names.remove("Bob");
        
        // Checking if an element is present
        boolean hasAlice = names.contains("Alice");
        System.out.println("Contains Alice: " + hasAlice);
        
        // Size of collection
        System.out.println("Size: " + names.size());
        
        // Clearing the collection
        names.clear();
    }
}

🔗 Related Notes