Wrapper Classes and Autoboxing in Java – Complete Tutorial

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Last Updated on: 25th Nov 2025 13:08:49 PM

Java is an Object-Oriented Programming (OOP) language, but primitive data types like int, char, float, etc. are not objects.
To bring primitives into the object world, Java provides Wrapper Classes.

 

Wrapper classes allow primitives to behave like objects—this is extremely useful in:

• Collections (ArrayList, HashMap, etc.)

• Frameworks (Hibernate, Spring)

• Method parameter passing

• Converting strings to numbers

• Handling null values

 

What Are Wrapper Classes? 

The wrapper class in Java provides the mechanism to convert primitive into object and object into primitive.

 

Java provides 8 wrapper classes, one for each primitive data type:

Primitive Type	Wrapper Class
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double
char	Character
boolean	Boolean

 

Why do we need Wrapper Classes?

Because primitives:

• cannot be stored in collections

• cannot be null

• don’t have methods

• are not objects

Wrapper classes provide useful methods like:

• Integer.parseInt()

• Double.valueOf()

• Character.isDigit()

Example:

int x = 10;
Integer obj = Integer.valueOf(x); // object form
System.out.println(obj.toString());

 

Real-Life Example: Why Wrapper Classes Are Needed?

Imagine you have an Online Shopping Cart implemented using ArrayList.
ArrayList stores only objects.

 

So you cannot write:

ArrayList<int> cart = new ArrayList<>();  // ❌ Not allowed

 

You must use:

ArrayList<Integer> cart = new ArrayList<>(); // ✔ Allowed

Here, Integer is the wrapper for int.

 

Autoboxing & Unboxing – The Most Important Topic

Java 5 introduced Autoboxing and Unboxing to reduce manual conversion. autoboxing and unboxing feature convert primitives into objects and objects into primitives automatically.

 

1. Autoboxing (Primitive → Wrapper Automatically)

Java automatically converts a primitive value to its wrapper object.

int a = 50;
Integer obj = a; // autoboxing
System.out.println(obj);

 

Output:

50

 

2. Unboxing (Wrapper → Primitive Automatically)

Java automatically converts an object of wrapper class back to a primitive.

Example:

Integer num = 100;
int n = num;  // unboxing
System.out.println(n);

Output:

100

 

Autoboxing & Unboxing – Full Practical Example

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

        // Autoboxing
        int a = 20;
        Integer obj = a;
        System.out.println("Autoboxing: " + obj);

        // Unboxing
        Integer num = 40;
        int b = num;
        System.out.println("Unboxing: " + b);
    }
}

 

Output:

Autoboxing: 20
Unboxing: 40

 

Manual Conversion (Before Autoboxing)

Before Java 5:

int a = 10;
Integer obj = Integer.valueOf(a); // manual boxing

Integer num = 20;
int b = num.intValue(); // manual unboxing

 

Wrapper Class Useful Methods (Very Important for Interviews)

 

parseInt()

Converts String → int

int x = Integer.parseInt("123");

 

valueOf()

Converts primitive → wrapper object

Integer n = Integer.valueOf(10);

 

toString()

Converts number → String

String s = Integer.toString(100);

 

Boolean Methods

Boolean bool = Boolean.valueOf(true);

 

Real-Life Example: Taking User Input

Scanner inputs come as Strings.
To convert:

Scanner sc = new Scanner(System.in);
System.out.print("Enter price: ");
String p = sc.nextLine();

int price = Integer.parseInt(p); // using Wrapper

 

Real-Life Example: Banking Transaction System

Bank logs are stored in objects, not primitives.

ArrayList<Double> transactions = new ArrayList<>();
transactions.add(1500.75);  // autoboxing
transactions.add(200.50);

 

No need to manually convert.

 

Important: Wrapper Classes Can Store NULL

Primitive:

int a = null;  // ❌ Error

 

Wrapper:

Integer a = null; // ✔ Allowed

 

Used in:

• Frameworks

• Databases (nullable fields)

• API responses

 

Wrapper Classes vs Primitive Types

Feature	Primitive	Wrapper
Memory	Fast & small	More memory
Methods	No	Yes
Can be null?	No	Yes
Used in Collections	No	Yes
Speed	Faster	Slower

 

When to Use Wrapper Classes?

Use Wrapper Classes when:

✔ Working with Collections
✔ Handling null values
✔ Using generics
✔ Converting string inputs
✔ Working with APIs / JSON / Databases
✔ Using Reflection

 

Complete Summary

• Wrapper classes convert primitives into objects.

• Autoboxing converts primitive → wrapper automatically.

• Unboxing converts wrapper → primitive automatically.

• Required for Collections, Frameworks, Generics, and real-world applications.

• Provide useful methods for data conversion.

 

Keep practicing — you're doing amazing!

Happy Coding!    

 

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