Why wrapper classes are used in Java - See It in Action

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Why Wrapper Classes Are Used in Java

📖 Scenario: Imagine you are working on a Java program that needs to store numbers and text together in a list. Java has two types of data: simple types like int and complex types like String. But simple types cannot be stored directly in lists that hold objects.

🎯 Goal: You will learn why wrapper classes are used in Java by creating a list that stores numbers as objects using wrapper classes.

📋 What You'll Learn

Create an ArrayList to store numbers as objects

Use the wrapper class Integer to store int values

Add numbers to the list using wrapper objects

Print the list to see the stored numbers

💡 Why This Matters

🌍 Real World

In real Java programs, wrapper classes are used to store simple values in collections, work with APIs that require objects, and use utility methods.

💼 Career

Understanding wrapper classes is important for Java developers to handle data structures, collections, and APIs effectively.

1

Create an ArrayList to store Integer objects

Write a line of code to create an ArrayList called numbers that can store Integer objects.

Java

// Your code here

💡 Need a hint?

Use ArrayList<Integer> to store integer objects.

2

Add int values to the ArrayList using Integer wrapper

Add the int values 10, 20, and 30 to the numbers list using the Integer wrapper class.

Java

import java.util.ArrayList;

ArrayList numbers = new ArrayList();
// Add 10, 20, and 30 to numbers using Integer wrapper
// Your code here

💡 Need a hint?

Use Integer.valueOf(value) to convert int to Integer.

3

Use a for loop to print each Integer in the list

Write a for loop using Integer num to go through numbers and print each number.

Java

import java.util.ArrayList;

ArrayList numbers = new ArrayList();
numbers.add(Integer.valueOf(10));
numbers.add(Integer.valueOf(20));
numbers.add(Integer.valueOf(30));
// Use a for loop to print each number
// Your code here

💡 Need a hint?

Use for (Integer num : numbers) to loop through the list.

4

Print the entire list to show stored Integer objects

Write a line to print the numbers list directly using System.out.println(numbers).

Java

import java.util.ArrayList;

ArrayList numbers = new ArrayList();
numbers.add(Integer.valueOf(10));
numbers.add(Integer.valueOf(20));
numbers.add(Integer.valueOf(30));
for (Integer num : numbers) {
    System.out.println(num);
}
// Print the entire numbers list
// Your code here

💡 Need a hint?

Use System.out.println(numbers) to print the whole list.