Q) What are wrapper classes?

A)

->for each primitive data type a corresponding java class is given in java.long.package.

These 8 library classes corresponding to 8 primitive data types are known as wrapper class.

->An instance of wrapper class wraps (encapsulates) a primitive value and hence the name.

Primitive data type	Wrapper class
int	Integer
byte	Byte
short	Short
long	Long
float	Float
double	Double
char	character
boolean	Boolean

->the java is not purely 100% object oriented, because it contains primitive data types. If any language contains primitive data types then that language is not pure object oriented.

->but the pure object oriented language is smalltalk.

->Wrapper object:

Object oriented manner an object is encapsulate the primitive value. That object is called wrapper object.

Ex:

Int a=10;

Integer i=nre Integer(10);

->to convert a primitive value into wrapper object create the object of wrapper class by supplying primitive alue as argument to the parameterized constructor of the wrapper class.

Ex:

Integer i= new Integer(10);

Boolean b=new Boolean(true);

Float f= new Float(1.1);

Double d=new Double(2.5);

->By calling xxxvalue(); method on the wrapper object we can get the primitive value.

Ex:

int a= i.intValue();

boolean flag= b.booleanValue();

double b=d.doubleValue();

-> Conversion of object type to primitive type.

->integer i=new Integer(10);  then the Integer class of encapsulated in the Integer object.

Ex:

class wrapperclass {

       public static void main(String[] args) {

                     Integer i=new Integer(10);

                     int c=40;

                     //intb=i.intValue(10);

                     int b=i+c; //doesn't work before jdk 1.5

                     System.out.println("b: "+b);

       }

}

Output:

b: 50

->implicit conversion of wrapper object to primitive type is known as auto unboxing. It is introduced in jdk1.5.

int b=i+c;

->in the above statement, Integer object I is implicitly converted into primitive value then arithmetic operation is performed. I.e. auto unboxing is implemented and then addition is performed.