Wrapper classes in Java

Wrapper classes provide a way to use primitive data types (int, boolean, etc..) as objects. The wrapper class in Java provides the mechanism to convert primitive into object and object into primitive.

Use of Wrapper classes in Java:

• Change the value in Method: Java supports only call by value. So, if we pass a primitive value, it will not change the original value. But, if the primitive value is converted to an object, it will change the original value.
• Serialization: The objects are needed to convert into streams to perform the serialization. If there is a primitive value, convert it to object through the wrapper classes.
• Synchronization: Java synchronization works with objects in Multithreading.
• java.util package: The java.util package provides the utility classes to deal with objects.
• Collection Framework: Java collection framework works with objects only. All classes of the collection framework (ArrayList, LinkedList, Vector, HashSet, LinkedHashSet, TreeSet, PriorityQueue, ArrayDeque, etc.) deal with objects only.

The eight classes of the java.lang package are known as wrapper classes in Java. 

Primitive Data Type	Wrapper Class
Byte	Byte
Short	Short
Int	Integer
Long	Long
Float	Float
double	Double
boolean	Boolean
Char	Character

 

Ex:

//Java Program to convert all primitives into its corresponding wrapper objects and vice-versa  

public class WrapperEx{ 

public static void main(String args[]){ 

byte b=10; 

short s=20; 

int i=30; 

long l=40; 

float f=50.0F; 

double d=60.0D; 

char c='a'; 

boolean b2=true; 

 

//Autoboxing: Converting primitives into objects 

Byte byteobj=b; 

Short shortobj=s; 

Integer intobj=i; 

Long longobj=l; 

Float floatobj=f; 

Double doubleobj=d; 

Character charobj=c; 

Boolean boolobj=b2; 

 

//Printing objects 

System.out.println("---Printing object values---"); 

System.out.println("Byte object: "+byteobj); 

System.out.println("Short object: "+shortobj); 

System.out.println("Integer object: "+intobj); 

System.out.println("Long object: "+longobj); 

System.out.println("Float object: "+floatobj); 

System.out.println("Double object: "+doubleobj); 

System.out.println("Character object: "+charobj); 

System.out.println("Boolean object: "+boolobj); 

 

//Unboxing: Converting Objects to Primitives 

byte bytevalue=byteobj; 

short shortvalue=shortobj; 

int intvalue=intobj; 

long longvalue=longobj; 

float floatvalue=floatobj; 

double doublevalue=doubleobj; 

char charvalue=charobj; 

boolean boolvalue=boolobj; 

 

//Printing primitives 

System.out.println("---Printing primitive values---"); 

System.out.println("byte value: "+bytevalue); 

System.out.println("short value: "+shortvalue); 

System.out.println("int value: "+intvalue); 

System.out.println("long value: "+longvalue); 

System.out.println("float value: "+floatvalue); 

System.out.println("double value: "+doublevalue); 

System.out.println("char value: "+charvalue); 

System.out.println("boolean value: "+boolvalue); 

}}