ArrayList: The Dynamic Alternative

In Java, a standard Array is like a fixed-size parking lot—once you build it for 10 cars, you can never park an 11th one. An ArrayList, however, is like an accordion; it grows and shrinks automatically as you add or remove items.

1. Key Differences

2. Importing and Creating

To use it, you must import it from the java.util package.

import java.util.ArrayList;

// Syntax: ArrayList<DataType> name = new ArrayList<>();
ArrayList<String> tools = new ArrayList<>();

3. Common Operations

4. ArrayList with Primitive Types

Since ArrayLists only store Objects, you cannot use int, double, or boolean directly. Instead, Java uses Wrapper Classes:

• int → Integer
• double → Double
• boolean → Boolean

ArrayList<Integer> scores = new ArrayList<>(); // Correct
// ArrayList<int> scores = new ArrayList<>(); // Error!

💻 Full Practical Example: The Task Manager

Copy this code to see how easy it is to manage a changing list of data:

import java.util.ArrayList;
import java.util.Collections; // Bonus: for sorting!

public class TaskList {
    public static void main(String[] args) {
        ArrayList<String> tasks = new ArrayList<>();

        // Adding items
        tasks.add("Fix Hyprland config");
        tasks.add("Complete Java Lab");
        tasks.add("Buy thermal paste");

        // Removing an item
        tasks.remove(0); 

        // Checking the list
        System.out.println("Remaining Tasks: " + tasks.size());

        // Sorting the list alphabetically
        Collections.sort(tasks);

        // Standard Loop
        for (int i = 0; i < tasks.size(); i++) {
            System.out.println((i + 1) + ". " + tasks.get(i));
        }
    }
}

💡 Challenge: The Dynamic Inventory

1. Create an ArrayList of String called inventory.
2. Add four items to it (e.g., "CPU", "GPU", "RAM", "SSD").
3. Use an if statement with .contains("GPU") to check if a graphics card is in stock.
4. Replace "SSD" with "M.2 NVMe" using the .set() method.
5. Print the final list using a ForEach loop.