Wrapper Class in Java

Last Updated: 28 May, 2022

Java wrapper class provides a mechanism to convert primitive data types (int, float, char, boolean, etc.) into corresponding objects (Integer, Float, Character, Boolean, etc.). A Wrapper class wraps or contains primitive values into a wrapper class object.

• Java 1.5 Version introduced the Wrapper class.
• java.lang Package provides all 8 Wrapper Classes for each of the primitive data.
• All the Wrapper classes are by default Final and immutable so their state can not be changed.

In the table, we can see the Primitive Data types and their Corresponding Wrapper class:

Why Wrapper classes are needed in Java

• Java supports only call by value. So, if we pass a primitive value, it will not change the original value. But, if we convert the primitive value into an object, it will change the original value.
• The Utility classes in java.util package only deals with objects.
• Data structures in the collection framework only store objects such as ArrayList, Vector, HashSet, TreeSet, etc.
• In multithreading, to perform synchronization we need objects not primitive.
• We cannot perform Serialization with primitive types, Serialization works with Objects only.
• We cannot assign null using primitive type if required but using wrapper we can do so.

Autoboxing and Unboxing in Java

Autoboxing: Autoboxing is the process of converting a primitive datatype to its corresponding Wrapper class.

For example, int to Integer, char to Character, double to Double, float to Float, long to Long, boolean to Boolean, short to Short, byte to Byte.

Example 1 : Primitive to Wrapper Conversion (Autoboxing)

import java.util.ArrayList; public class AutoboxingDemo { public static void main(String[] args) { int number = 100; //Autoboxing - Primitive to Wrapper conversion Integer result = number; System.out.println("Wrapper value : " + result); ArrayList<Integer> list = new ArrayList<Integer>(); // Here, we are passing primitive but // internally it converts into corresponding wrapper list.add(number); System.out.println("Wrapper name: " + list.get(0).getClass()); System.out.println("ArrayList value: " + list.get(0)); } }

Output

Wrapper value : 100
Wrapper name: class java.lang.Integer
ArrayList value: 100

Unboxing: It is a reverse process of autoboxing, It converts a Wrapper class object into its corresponding Primitive Datatype.

For example, Integer to int, Character to char, Double to double, Float to float, Long to long, Boolean to boolean, Short to short, Byte to byte.

Example 2 : Wrapper to Primitive Conversion (Unboxing)

import java.util.ArrayList; public class UnboxingDemo { public static void main(String[] args) { Integer number = 100; // UnBoxing - Wrapper to Primitive conversion int result = number; System.out.println("Primitive value 1 : " + result); ArrayList<Integer> list = new ArrayList<Integer>(); list.add(500); int value = list.get(0); System.out.println("Primitive value 2 : " + value); } }

Output

Primitive value 1 : 100
Primitive value 2 : 500