10-Collections.java

* Collection in Java?

👉 Collection means a group of objects.
In Java, the Collection Framework helps us store and manage data easily.

Example:
Instead of storing 100 variables, we store them inside a collection like ArrayList.

🔹 Main Types of Collections

- There are 3 important interfaces:

i]   List – Allows duplicates, maintains order

ii]  Set – No duplicates

iii] Map – Stores key-value pairs


1️⃣ List (ArrayList Example)

✔ Allows duplicate values
✔ Maintains insertion order

Example :     import java.util.ArrayList;
              public class Main 
              {
              public static void main(String[] args)
              {

              ArrayList<String> names = new ArrayList<>();

              names.add("Yuva");
              names.add("Yuvi");
              names.add("Babloo");

              System.out.println("Names in list:");
              for(String name : names)
              {
              System.out.println(name);
        }
    }
}       


2️⃣ Set (HashSet Example)

✔ Does NOT allow duplicates
✔ Order is not guaranteed

import java.util.HashSet;

public class Main 
{
public static void main(String[] args) 
{

        HashSet<String> cities = new HashSet<>();

        cities.add("Mysuru");
        cities.add("Bangalore");
        cities.add("Mysuru"); // duplicate

        System.out.println("Cities:");
        System.out.println(cities);
    }
}


3️⃣ Map (HashMap Example)

✔ Stores data in key-value format
✔ Keys must be unique

import java.util.*;
public class MapExample 
{
    public static void main(String[] args) 
{
        HashMap<Integer, String> students = new HashMap<>();

        students.put(1, "Yuvi");
        students.put(2, "Babloo");

        System.out.println(students);
    }
}


| Feature    | List  | Set  | Map       |
| ---------- | ----- | ---- | --------- |
| Duplicates | ✅ Yes | ❌ No | ❌ Keys No |
| Order      | ✅ Yes | ❌ No | ❌ No      |
| Index      | ✅ Yes | ❌ No | ❌ No      |