10.md

Collections

In Java, collections are like containers that can hold multiple items. They help us store, organize, and manage groups of objects. Let's learn about some common types of collections: List, Set, and Map.

Introduction to Collections

Collections are used to store and manage groups of objects. They provide various methods to add, remove, and access elements. Java provides a framework called the Collections Framework to work with collections easily.

List Interface

A List is a collection that can hold a sequence of elements. You can access elements by their position (index) in the list. Lists can contain duplicate elements.

Example: Using an ArrayList

import java.util.ArrayList;

public class ListExample {
    public static void main(String[] args) {
        // Create an ArrayList to store names
        ArrayList<String> names = new ArrayList<>();

        // Add names to the list
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");
        names.add("Alice"); // Duplicate element

        // Print the list
        System.out.println("Names: " + names);

        // Access an element by index
        String name = names.get(1);
        System.out.println("Name at index 1: " + name);

        // Remove an element
        names.remove(2);
        System.out.println("Names after removing: " + names);
    }
}

Set Interface

A Set is a collection that cannot contain duplicate elements. Sets are useful when you need to store unique items.

Example: Using a HashSet

import java.util.HashSet;

public class SetExample {
    public static void main(String[] args) {
        // Create a HashSet to store unique numbers
        HashSet<Integer> numbers = new HashSet<>();

        // Add numbers to the set
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        numbers.add(20); // Duplicate element, will be ignored

        // Print the set
        System.out.println("Numbers: " + numbers);
    }
}

Map Interface

A Map is a collection that stores key-value pairs. You can access values by their corresponding keys.

Example: Using a HashMap

import java.util.HashMap;

public class MapExample {
    public static void main(String[] args) {
        // Create a HashMap to store names and ages
        HashMap<String, Integer> people = new HashMap<>();

        // Add entries to the map
        people.put("Alice", 25);
        people.put("Bob", 30);
        people.put("Charlie", 20);

        // Print the map
        System.out.println("People: " + people);

        // Access a value by key
        int age = people.get("Bob");
        System.out.println("Bob's age: " + age);

        // Update a value
        people.put("Alice", 26);
        System.out.println("People after updating: " + people);
    }
}

Collections are powerful tools in Java that help us work with groups of objects efficiently. By using the right type of collection, you can write more efficient and effective code.

---

<< Previous | Home | Next >>