Autoboxing in Java - Mini Project: Build & Apply

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Autoboxing in Java

📖 Scenario: Imagine you are managing a small store's inventory system. You need to work with product quantities, which are numbers. Sometimes you use simple numbers, and sometimes you need to use objects that hold numbers. Java helps by automatically converting between these two forms, called autoboxing.

🎯 Goal: You will create a Java program that shows how autoboxing works by converting between primitive int and the wrapper class Integer. You will store numbers in an ArrayList of Integer and perform simple operations.

📋 What You'll Learn

Create an ArrayList of Integer to hold product quantities.

Add primitive int values to the ArrayList using autoboxing.

Retrieve values from the ArrayList and use them as primitive int using unboxing.

Calculate the total quantity of all products.

Print the total quantity.

💡 Why This Matters

🌍 Real World

Autoboxing helps when working with collections like <code>ArrayList</code> that cannot hold primitive types directly. It makes code simpler and cleaner by automatically converting between primitives and objects.

💼 Career

Understanding autoboxing is important for Java developers because it is used frequently in everyday coding, especially when handling data collections, APIs, and frameworks that require objects instead of primitives.

1

Create an ArrayList of Integer

Create an ArrayList called quantities that can hold Integer objects.

Java

// Your code here

💡 Need a hint?

Use ArrayList<Integer> and the new keyword to create the list.

2

Add primitive int values to the ArrayList

Add the primitive int values 10, 20, and 30 to the quantities ArrayList. Java will autobox them to Integer objects.

Java

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList quantities = new ArrayList();
        // Add 10, 20, and 30 to quantities
        // Your code here
    }
}

💡 Need a hint?

Use the add method to add each number directly. Java will convert the int to Integer automatically.

3

Calculate the total quantity using unboxing

Create an int variable called total and set it to 0. Use a for loop with variable qty to iterate over quantities. Add each qty to total. This uses unboxing to convert Integer to int automatically.

Java

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList quantities = new ArrayList();
        quantities.add(10);
        quantities.add(20);
        quantities.add(30);
        int total = 0;
        // Use a for loop with qty to add each quantity to total
        // Your code here
    }
}

💡 Need a hint?

Use a for-each loop to go through quantities. Add each qty to total.

4

Print the total quantity

Write a System.out.println statement to print the text Total quantity: followed by the value of total.

Java

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList quantities = new ArrayList();
        quantities.add(10);
        quantities.add(20);
        quantities.add(30);
        int total = 0;
        for (Integer qty : quantities) {
            total += qty;
        }
        // Print the total quantity
        // Your code here
    }
}

💡 Need a hint?

Use System.out.println with a string and the total variable to show the result.