Boxing, unboxing, and autoboxing

1. Overview

Let's clarify what boxing, unboxing, and autoboxing are and Why it needs and how to work.

2. Description

2.1 Definition

Name	Definition	Invoking cases
Autoboxing	Converting a primitive value into an object of the corresponding wrapper class	Passed as a parameter to a method that expects an object of the corresponding wrapper class Assigned to a variable of the corresponding wrapper class
(auto)Unboxing	Converting an object of a wrapper type to its corresponding primitive value	Passed as a parameter to a method that expects a value of the corresponding primitive type Assigned to a variable of the corresponding primitive type

2.2 Corresponding Table of each type

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

3. Examples

3.1 Common cases

// Java program to illustrate the concept 
// of Autoboxing and Unboxing 
import java.io.*; 
  
class GFG 
{ 
    public static void main (String[] args) 
    { 
        // creating an Integer Object 
        // with value 10. 
        // also can treat it boxing(explicitly)
        Integer i = new Integer(10); 
  
        // (auto)unboxing the Object 
        int i1 = i; 
  
        System.out.println("Value of i: " + i); 
        System.out.println("Value of i1: " + i1); 
  
        //Autoboxing of char 
        Character gfg = 'a'; 
  
        // Auto-unboxing of Character 
        char ch = gfg; 
        System.out.println("Value of ch: " + ch); 
        System.out.println("Value of gfg: " + gfg); 
  
    } 
} 

3.2 Generics related cases

/* Java program to illustrate autoboxing */
import java.io.*; 
import java.util.*; 
  
class GFG 
{ 
    public static void main (String[] args) 
    { 
        /* Here we are creating a list 
          of elements of Integer type. 
          adding the int primitives type values */
        List<Integer> list = new ArrayList<Integer>(); 
        for (int i = 0; i < 10; i++) 
            list.add(i); 
    } 
} 


/* Java program to illustrate autoboxing */
import java.io.*; 
import java.util.*; 
  
class GFG 
{ 
    public static void main (String[] args) 
    { 
        /* Here we are creating a list of elements 
          of Integer type. Adding the int primitives 
          type values by converting them into Integer 
          wrapper Object*/
        List<Integer> list = new ArrayList<Integer>(); 
        for (int i = 0; i < 10; i++) 
        	// here is the autoboxing occurred
            list.add(Integer.valueOf(i)); 
  
    } 
} 


// Java program to illustrate  find sum 
// of odd numbers using autobxing and unboxing 
import java.io.*; 
import java.util.*; 
  
class GFG 
{ 
    public static int sumOfOddNumber(List<Integer> list) 
    { 
        int sum = 0; 
        for (Integer i : list) 
        { 
            // unboxing of i automatically 
            if(i % 2 != 0) 
                sum += i; 
            /* unboxing of i is done automatically 
               using intvalue implicitly 
            if(i.intValue() % 2 != 0) 
                sum += i.intValue();*/
        } 
        return sum; 
    } 
  
    public static void main (String[] args) 
    { 
        /* Here we are creating a list of elements 
           of Integer type and adding the int primitives 
           type values to the list*/
        List<Integer> list = new ArrayList<Integer>(); 
        for (int i = 0; i < 10; i++) 
            list.add(i); 
  
        // getting sum of all odd no. in the list. 
        int sumOdd = sumOfOddNumber(list); 
        System.out.println("Sum of odd numbers = " + sumOdd); 
    } 
} 

4. References

https://www.geeksforgeeks.org/autoboxing-unboxing-java/

https://docs.oracle.com/javase/tutorial/java/data/autoboxing.html

https://www.studytonight.com/java/autoboxing-unboxing-java.php