Wrapper Classes

• Using wrapper classes we can wrap the concept of object on the top of the primitive data.
• And represent the primitive data values in the form of its equivalent objects.
• In order to represent the 8 primitive data values in the form of its equivalent objects we have 8 wrapper classes they are
  
  1. Byte
  2. Short
  3. Integer
  4. Long
  5. Double
  6. Float
  7. Character
  8. Boolean
   

Uses of wrapper classes: 

• Using wrapper classes we can represent the primitive data  values in form of its equivalent objects.
• many time it would be required to represent the primitive data values in the form of objects
  ex: Collections, Session
• Wrapper classes supports the functions using which we can get back the sequence of primitive data characters present inside the string class object back into its corresponding data value.
• It has two constructors
  
  1. Accepts the values of primitive data
  2. Accepts the object of String class
   
• Syntax:
      Integer num1=new Integer(12);
      Integer num2=new Integer("12");
• To get the value form it
   int n=num2.intValue();
  
  

Integer wrapper class Example program:

package com.instanceofjavaforus;

public class wrapperDemo {

public static void main(String args[]){

    int x=12;
   
    Integer num1=new Integer(x);
    System.out.println(num1);
    num1=num1+1;
    System.out.println(num1);
    String str="12";
    Integer num2= new Integer(str);
    System.out.println(num2);
   
    int num3=num2.intValue();
   
    System.out.println(num3);
}

}

Output:

12
13
12
12

Example program 2 on Integer wrapper class:

package com.instanceofjavaforus;
public class Wraperdemo2 {
    public static void main(String args[]){
  
        String s1="12";
        Integer i=new Integer(s1);
       
        int x=i.intValue();
       
        System.out.println(x);
        String s2="abc";
        Integer i2=new Integer(s2);// no compilation error but run time error will come
       
        String s3=" 123";
       
        Integer i3= new Integer(s3);// run time error
         i3= new Integer(s3.trim());// recommended to trim
    }

}

• String s2="abc"
  Integer i2=new Integer(s2);// no compilation error but run time error will come.
• It accepts String class object but the string should contain only integer otherwise the constructor dont know how to represent characters gives error.
•    String a=" 123";
• here some times there may be a chance of having spaces in a string so it is recommended to trim the object
•    i3= new Integer(s3.trim());// recommended to trim

Program 3 :
package com.instanceofjavaforus;

public class wraperDemo3{
public static void main(String args[]){

        String s1="12";
        Integer i=new Integer(s1);
       
        int x=i.intValue();
        System.out.println(x);

        String s2="123";
        int y= Integer.parseInt(s2.trim());
    }
}
Output:
12