Autoboxing and Unboxing in Java

Overview

In this tutorial, we will learn about Autoboxing and Unboxing in Java. This features were introduced in J2SE 5.

Autoboxing

Autoboxing is the automatic conversion by the Java complier of the primitive type to the corresponding Wrapper class object.

Example:
Converting an int type to an Integer wrapper class object.

Integer i = 9; // autoboxing int to Integer

Character c = ‘a’; // autoboxing char to Character

Table that shows the Java primitive types and the corresponding Wrapper classes.

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

Sample Code

public class AutoBoxingDemo {
 public static void main(String[] args) {
 ArrayList list = new ArrayList<>();
 for (int i = 1; i < 10; i++) { 
 // int to -> Integer 
 list.add(Integer.valueOf(i));
 }
 }
}

AutoBoxing Java Program

In the above code snippet list is a list of Integer objects. In the loop we have added int primitives type to the list. Notice that, Java complier does not complain about the type mismatch. The complier creates an Integer object from i and adds to the list. This conversion is called autoboxing. Autoboxing can be done during assignment, method invocation, etc.

Unboxing

Unboxing is the reverse conversion. It is the automatic conversion of Wrapper class object to their corresponding primitive type by the Java compiler.

Sample Code Example

import java.util.ArrayList;

//UnBoxing Demo Program
//Java Tutorials - www.TestingDocs.com
public class UnBoxingDemo {
 public static void main(String[] args) {
 int primInt = 0;
 Integer i = Integer.valueOf(9);

 // Unboxing through assignment
 ArrayList list = new ArrayList<>();
 list.add(3.14f);
 float f = list.get(0);

 // Unboxing through method call
 primInt = foo(i);
 System.out.println(primInt);
 }

 public static int foo(int i) {
 return i;
 }

}

Unboxing in Java Demo Program