Wrapper Classes

Wrapper Classes:-

In a java wrapper classes are used to convert primitive data type to object type and object to primitive data type. Sometimes we have object but that time we need variable and sometime data (variable) is available but that time we need object to execute method of the particular class.

For example:-we have to create object of Integer class.

Integer ob=new Integer(100);   or

Integer ob=new Integer(“100”);

Every wrapper class contains two constructor one common String argument constructor except Character class, it contains only one constructor.

type	Wrapper classes
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double
char	Character
boolean	Boolean

Wrapper classes	Constructor
Byte	new Byte(byte)      ,    new Byte(String)
Short	new Short (short)   ,    new Short(String)
Integer	new Integer(int)      ,    new Integer(String)
Long	new Long(long)      ,    new Long(String)
Float	new Float(float)      ,    new Float(String)
Double	new Double (double)      ,    new Double(String)
Character	new Character (char)
Boolean	new Boolean(boolean)     ,     new Boolean(String)

      

Example1:- TestWrapper.java

class TestWrapper

{

public static void main(String[]args)

{

Integer ob=new Integer(100);

int i=ob.intValue();

System.out.println(i);

}

}

Output:-100

Example2:- TestWrapper.java

class TestWrapper

{

public static void main(String[]args)

{

Integer ob=new Integer(100);

int i=i.intValue();

System.out.println(i);

}

}

Output:- C:\JAVATECH>javac TestWrapper.java

TestWrapper.java:6: error: int cannot be dereferenced

int i=i.intValue();

       ^1 error

Example3:- TestWrapper.java

class TestWrapper

{

public static void main(String[]args)

{

Integer ob=new Integer("100");

System.out.println("Object "+ob);

int i=ob.intValue();

System.out.println("int "+i);

}

}

Output:-

C:\JAVATECH>javac TestWrapper.java

C:\JAVATECH>java TestWrapper

Object 100

int 100

Example4:- TestWrapper.java

class TestWrapper

{

public static void main(String[]args)

{

Integer ob=new Integer("100");

int i=ob.intValue();

System.out.println(i+100);

System.out.println("integer object to String object conversion with proof");

String s=ob.toString();

System.out.println(s+100);

}}

Output:- C:\JAVATECH>javac TestWrapper.java

C:\JAVATECH>java TestWrapper

200

integer object to String object conversion with proof

100100

Example5:- TestWrapper.java

class TestWrapper

{

public static void main(String[]args)

{

Integer ob=new Integer("100");

int i=ob.intValue();

System.out.println(i+100);

System.out.println("integer object to String object conversion with proof");

String s=ob.toString();

System.out.println(s+100);

System.out.println("String object to int conversion with proof");

Integer ob1=new Integer(s);

int p=ob1.intValue();

System.out.println(p+100);

}

}

Output:- C:\JAVATECH>javac TestWrapper.java

C:\JAVATECH>java TestWrapper

200

integer object to String object conversion with proof

100100

String object to int conversion with proof

200

Autoboxing & Autounboxing:-java support autoboxing that means normal variable automatically convert into related object and object convert into related variable called autounboxing. .

Example1:-Test.java

class Test

{

public static void main(String[]args)

{

int i=100;

Integer ob=i;

System.out.println(ob);

int p=ob;

System.out.println(p);

}

}

Output:-

C:\JAVATECH>javac Test.java

C:\JAVATECH>java Test

100

100