Why to use wrapper class?

Question

hello,
can anybody please tell me why wrapper class are used in JAVA and what are exactly wrapper class?
reply me soon....

Answer 1

I want to give an example and then explain why it is for. Primitives will be good example for this situation.
Example:
Below are the primitive types and their wrapper classes...
Primitive to Wrapper Class
byte - Byte
short - Short
int - Integer
long - Long
char - Character
float - Float
double - Double
boolean - Boolean
USING OBJECT CREATION
Think a situation when you create an integer object using this code:
---> Integer intVar = new Integer();
you have the methods and constants:
1 MAX_VALUE ,
2 MIN_VALUE ,
3 byteValue() ,
4 compareTo(Integer anotherInteger) ,
5 compareTo(Object o) ,
6 decode(String nm) ,
7 doubleValue() ,
8 equals(Object obj) ,
9 floatValue() ,
10 getInteger(String nm) ,
11 getInteger(String nm, int val) ,
12 getInteger(String nm, Integer val) ,
13 hashCode() ,
14 intValue() ,
15 longValue() ,
16 parseInt(String s) ,
17 parseInt(String s, int radix) ,
18 shortValue() ,
19 toBinaryString(int i) ,
20 toHexString(int i) ,
21 toOctalString(int i) ,
22 toString(),
23 toString(int i) ,
24 toString(int i, int radix) ,
25 valueOf(String s) ,
26 valueOf(String s, int radix)
now you have an object with 2 constants and 24 methods.
USING WRAPPER CLASS
and think using wrapper class of Integer..
CODE ---> int intVar = Integer.parseInt((String)someStringData);
In this case your Integer object have the methods and constants
1 MAX_VALUE ,
2 MIN_VALUE ,
3 parseInt(String s) ,
4 parseInt(String s, int radix) ,
5 toBinaryString(int i) ,
6 toHexString(int i) ,
7 toOctalString(int i) ,
8 toString(int i) ,
9 toString(int i, int radix) ,
10 valueOf(String s) ,
11 valueOf(String s, int radix)
as you in this situation you have 2 constants and 9 methods.
AS YOU SEE THERE ARE 15 METHODS DIFFERENCE FROM THE OBJECT AND THE WRAPPER CLASS OF INTEGER OBJECT.
NOW TALKING ABOUT PRIMITIVE TYPES ALL PROGRAMMERS USED THIS TYPES FOR THEIR CODES AND THEY ALWAYS NEED SOME THIS KIND OF CASTING. IN MY EXAMPLE I TAKE THE VALUE OF AN STRING VARIABLE. AND THERE ARE LOTS OF THINGS SIMILIAR TO THIS EXAMPLE.
IDEA OF THIS WRAPPER CLASSES IS THAT USE AS YOU NEED NOTHING MORE. IN THE WRAPPER CLASS YOU DONT HAVE INTEGER OBJECT. YOU ONLY NEED THE PARSEINT METHOD OF INTEGER OBJECT INSTEAD OF CREATING THE INTEGER OBJECT YOU USE THE WRAPPER CLASS OF THIS TYPE...
OBJECTS ARE STORED IN A MEMORY PLACE CALLED HEAP WHICH IS PLACED ON RAM AND GARBAGING OF THIS OBJECTS TAKES MORE TIME TO ALLOCATE FROM HEAP STORAGE.
AND ANOTHER NOTE FOR THIS WRAPPER CLASSES if you want to store an int inside a container such as an ArrayList (which takes only Object references), you can wrap your int inside the standard library Integer class
EX:
import java.util.*;
public class ImmutableInteger {
public static void main(String[] args) {
List v = new ArrayList();
for(int i = 0; i < 10; i++)
v.add(new Integer(i));
// But how do you change the int inside the Integer?
} ///:~
GOOD LUCK...
REALKINGTA....