Autoboxing in Java

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Introduction

Autoboxing lets Java automatically convert simple values like numbers into objects, so you don't have to do it yourself.

When you want to store a simple number in a collection like ArrayList that only accepts objects.

When you want to pass a simple value to a method that expects an object.

When you want to mix simple values and objects without writing extra code to convert them.

When you want cleaner and easier-to-read code without manual conversions.

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Syntax

Java

Integer obj = 10; // int 10 is autoboxed to Integer object
Double dObj = 3.14; // double 3.14 is autoboxed to Double object

Autoboxing happens automatically when assigning a primitive value to its wrapper class.

Wrapper classes include Integer, Double, Boolean, etc., which are object versions of primitives.

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Examples

line_end_arrow_notchHere, the int 5 is automatically converted to an Integer object.

Java

Integer num = 5; // int 5 autoboxed to Integer

line_end_arrow_notchThe double value 9.99 is automatically boxed into a Double object.

Java

Double price = 9.99; // double 9.99 autoboxed to Double

line_end_arrow_notchThe boolean true is automatically converted to a Boolean object.

Java

Boolean flag = true; // boolean true autoboxed to Boolean

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Sample Program

This program shows autoboxing by adding int values directly to an ArrayList of Integer objects. Java converts the ints to Integer objects automatically.

Java

import java.util.ArrayList;

public class AutoboxingExample {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();
        
        // Autoboxing: int 10 is automatically converted to Integer object
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        
        // Print all numbers
        for (Integer num : numbers) {
            System.out.println(num);
        }
    }
}

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Important Notes

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Autoboxing makes code simpler but can add small performance overhead because of object creation.

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Be careful when comparing wrapper objects with ==; use .equals() to compare values.

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Summary

Autoboxing automatically converts primitive values to their wrapper objects.

It helps when working with collections or APIs that require objects.

Use autoboxing for cleaner and easier code without manual conversions.