Part 1 — Definition

An ArrayList is a resizable array found in the java.util package. Unlike standard arrays, which have a fixed size, an ArrayList can grow or shrink automatically as items are added or removed. It maintains the Insertion Order of elements.

Part 2 — Syntax

import java.util.ArrayList;
ArrayList<String> list = new ArrayList<>();
list.add("Item");
list.remove(0);

Part 3 — Example

Problem: Manage a "Shopping List" where users can add items.

ArrayList<String> cart = new ArrayList<>();
cart.add("Laptop");
cart.add("Mouse");

for(String item : cart) {
    System.out.println("Item in cart: " + item);
}

Part 4 — Video

Video: Coming Soon

Part 1 — Definition

A HashMap stores items in "Key/Value" pairs. You access an item by its key (e.g., an ID), which makes it incredibly fast for searching. Keys must be unique, while values can be duplicated.

Part 2 — Syntax

import java.util.HashMap;
HashMap<Integer, String> map = new HashMap<>();
map.put(101, "Ali");
String val = map.get(101);

Part 3 — Example

Problem: Store student IDs and their corresponding names.

HashMap<Integer, String> students = new HashMap<>();
students.put(1, "John");
students.put(2, "Sara");

System.out.println("ID 1 is: " + students.get(1));

Part 4 — Video

Video: Coming Soon