Wrapper class

Wrapper class

The classes which are used to represent primitive values as object are called wrapper classes.

Wrapper classes are used in project especially in collections, serialization, synchronization etc.!

under Java.lang package we have 8 wrapper classes one per each primitive type to represent them as object.

Data type's	Wrapper object
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double
char	Character
boolean	Boolean

 

1) Auto Boxing

Converting primitive datatypes into wrapper class object is called auto boxing

 

2) Auto un-boxing

Converting wrapper class object into primitive datatypes is called auto un-boxing

 

Note: auto boxing, unboxing new feature of Java5 program doesn’t  need to write conversion code.

to perform conversion operations, we have different type conversion operations in wrapper class objects.

  

1) primitive data type to wrapper object conversion

    int i = 10;

    Integer j = Integer.valueOf(i);

    //explicitly converting int to Integer.

System.out.println(j);

 

2) wrapper class object into primitive data type conversion

Integer a = Integer.valueOf(10);

      int b = a.intValue();

      //converting Integer to int explicitly

      System.out.println(b);

 

3) string object to wrapper class object conversion

String a = "123";

   System.out.println(“string to integer conversion”+ Integer.valueOf(a));

 
4) String object to primitive datatype conversion

String strObject = "124";

     int i = Integer.parseInt(strObject);

     System.out.println("String to int: " + i); 

5) wrapper class object to string object conversion

     Integer i = 100;

     System.out.println(i);

     // String name = i; //error still it is in int format

     String stringFormat = i.toString();

     String name = stringFormat;

     System.out.println(name);

     // now it is coverted to string format