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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
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